forked from mirrors/gecko-dev
6eed48f280
It's not used in a useful way. Differential Revision: https://phabricator.services.mozilla.com/D77210
843 lines
36 KiB
C++
843 lines
36 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
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/* vim: set ts=8 sts=2 et sw=2 tw=80: */
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/* This Source Code Form is subject to the terms of the Mozilla Public
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* License, v. 2.0. If a copy of the MPL was not distributed with this
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* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
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#ifndef dom_ipc_SharedPrefMap_h
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#define dom_ipc_SharedPrefMap_h
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#include "mozilla/AutoMemMap.h"
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#include "mozilla/HashFunctions.h"
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#include "mozilla/Preferences.h"
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#include "mozilla/Result.h"
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#include "mozilla/dom/ipc/StringTable.h"
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#include "nsDataHashtable.h"
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namespace mozilla {
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// The approximate number of preferences expected to be in an ordinary
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// preferences database.
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//
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// This number is used to determine initial allocation sizes for data structures
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// when building the shared preference map, and should be slightly higher than
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// the expected number of preferences in an ordinary database to avoid
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// unnecessary reallocations/rehashes.
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constexpr size_t kExpectedPrefCount = 4000;
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class SharedPrefMapBuilder;
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// This class provides access to a compact, read-only copy of a preference
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// database, backed by a shared memory buffer which can be shared between
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// processes. All state data for the database is stored in the shared memory
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// region, so individual instances require no dynamic memory allocation.
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//
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// Further, all strings returned from this API are nsLiteralCStrings with
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// pointers into the shared memory region, which means that they can be copied
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// into new nsCString instances without additional allocations. For instance,
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// the following (where `pref` is a Pref object) will not cause any string
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// copies, memory allocations, or atomic refcount changes:
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//
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// nsCString prefName(pref.NameString());
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//
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// whereas if we returned a nsDependentCString or a dynamically allocated
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// nsCString, it would.
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//
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// The set of entries is stored in sorted order by preference name, so look-ups
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// are done by binary search. This means that look-ups have O(log n) complexity,
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// rather than the O(1) complexity of a dynamic hashtable. Consumers should keep
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// this in mind when planning their accesses.
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//
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// Important: The mapped memory created by this class is persistent. Once an
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// instance has been initialized, the memory that it allocates can never be
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// freed before process shutdown. Do not use it for short-lived mappings.
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class SharedPrefMap {
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using FileDescriptor = mozilla::ipc::FileDescriptor;
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friend class SharedPrefMapBuilder;
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// Describes a block of memory within the shared memory region.
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struct DataBlock {
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// The byte offset from the start of the shared memory region to the start
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// of the block.
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size_t mOffset;
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// The size of the block, in bytes. This is typically used only for bounds
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// checking in debug builds.
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size_t mSize;
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};
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// Describes the contents of the shared memory region, which is laid-out as
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// follows:
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//
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// - The Header struct
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//
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// - An array of Entry structs with mEntryCount elements, lexicographically
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// sorted by preference name.
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//
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// - A set of data blocks, with offsets and sizes described by the DataBlock
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// entries in the header, described below.
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//
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// Each entry stores its name string and values as indices into these blocks,
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// as documented in the Entry struct, but with some important optimizations:
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//
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// - Boolean values are always stored inline. Both the default and user
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// values can be retrieved directly from the entry. Other types have only
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// one value index, and their values appear at the same indices in the
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// default and user value arrays.
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//
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// Aside from reducing our memory footprint, this space-efficiency means
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// that we can fit more entries in the CPU cache at once, and reduces the
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// number of likely cache misses during lookups.
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//
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// - Key strings are stored in a separate string table from value strings. As
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// above, this makes it more likely that the strings we need will be
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// available in the CPU cache during lookups by not interleaving them with
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// extraneous data.
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//
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// - Default and user values are stored in separate arrays. Entries with user
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// values always appear before entries with default values in the value
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// arrays, and entries without user values do not have entries in the user
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// array at all. Since the same index is used for both arrays, this means
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// that entries with a default value but no user value do not allocate any
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// space to store their user value.
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//
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// - For preferences with no user value, the entries in the default value are
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// de-duplicated. All preferences with the same default value (and no user
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// value) point to the same index in the default value array.
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//
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//
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// For example, a preference database containing:
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//
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// +---------+-------------------------------+-------------------------------+
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// | Name | Default Value | User Value | |
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// +---------+---------------+---------------+-------------------------------+
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// | string1 | "meh" | "hem" | |
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// | string2 | | "b" | |
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// | string3 | "a" | | |
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// | string4 | "foo" | | |
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// | string5 | "foo" | | |
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// | string6 | "meh" | | |
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// +---------+---------------+---------------+-------------------------------+
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// | bool1 | false | true | |
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// | bool2 | | false | |
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// | bool3 | true | | |
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// +---------+---------------+---------------+-------------------------------+
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// | int1 | 18 | 16 | |
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// | int2 | | 24 | |
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// | int3 | 42 | | |
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// | int4 | 12 | | |
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// | int5 | 12 | | |
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// | int6 | 18 | | |
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// +---------+---------------+---------------+-------------------------------+
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//
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// Results in a database that looks like:
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//
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// +-------------------------------------------------------------------------+
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// | Header: |
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// +-------------------------------------------------------------------------+
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// | mEntryCount = 15 |
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// | ... |
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// +-------------------------------------------------------------------------+
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//
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// +-------------------------------------------------------------------------+
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// | Key strings: |
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// +--------+----------------------------------------------------------------+
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// | Offset | Value |
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// +--------+----------------------------------------------------------------+
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// | 0 | string1\0 |
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// | 8 | string2\0 |
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// | 16 | string3\0 |
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// | 24 | string4\0 |
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// | 32 | string5\0 |
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// | 40 | string6\0 |
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// | 48 | bool1\0 |
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// | 54 | bool2\0 |
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// | 60 | bool3\0 |
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// | 66 | int1\0 |
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// | 71 | int2\0 |
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// | 76 | int3\0 |
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// | 81 | int4\0 |
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// | 86 | int6\0 |
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// | 91 | int6\0 |
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// +--------+----------------------------------------------------------------+
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//
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// +-------------------------------------------------------------------------+
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// | Entries: |
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// +---------------------+------+------------+------------+------------------+
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// | Key[1] | Type | HasDefault | HasUser | Value |
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// +---------------------+------+------------+------------+------------------+
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// | K["bool1", 48, 5] | 3 | true | true | { false, true } |
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// | K["bool2", 54, 5] | 3 | false | true | { 0, false } |
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// | K["bool3", 60, 5] | 3 | true | false | { true, 0 } |
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// | K["int1", 66, 4] | 2 | true | true | 0 |
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// | K["int2", 71, 4] | 2 | false | true | 1 |
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// | K["int3", 76, 4] | 2 | true | false | 2 |
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// | K["int4", 81, 4] | 2 | true | false | 3 |
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// | K["int5", 86, 4] | 2 | true | false | 3 |
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// | K["int6", 91, 4] | 2 | true | false | 4 |
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// | K["string1", 0, 6] | 1 | true | true | 0 |
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// | K["string2", 8, 6] | 1 | false | true | 1 |
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// | K["string3", 16, 6] | 1 | true | false | 2 |
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// | K["string4", 24, 6] | 1 | true | false | 3 |
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// | K["string5", 32, 6] | 1 | true | false | 3 |
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// | K["string6", 40, 6] | 1 | true | false | 4 |
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// +---------------------+------+------------+------------+------------------+
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// | [1]: Encoded as an offset into the key table and a length. Specified |
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// | as K[string, offset, length] for clarity. |
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// +-------------------------------------------------------------------------+
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//
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// +------------------------------------+------------------------------------+
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// | User integer values | Default integer values |
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// +-------+----------------------------+-------+----------------------------+
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// | Index | Contents | Index | Contents |
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// +-------+----------------------------+-------+----------------------------+
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// | 0 | 16 | 0 | 18 |
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// | 1 | 24 | 1 | |
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// | | | 2 | 42 |
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// | | | 3 | 12 |
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// | | | 4 | 18 |
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// +-------+----------------------------+-------+----------------------------+
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// | * Note: Tables are laid out sequentially in memory, but displayed |
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// | here side-by-side for clarity. |
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// +-------------------------------------------------------------------------+
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//
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// +------------------------------------+------------------------------------+
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// | User string values | Default string values |
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// +-------+----------------------------+-------+----------------------------+
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// | Index | Contents[1] | Index | Contents[1] |
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// +-------+----------------------------+-------+----------------------------+
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// | 0 | V["hem", 0, 3] | 0 | V["meh", 4, 3] |
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// | 1 | V["b", 8, 1] | 1 | |
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// | | | 2 | V["a", 10, 1] |
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// | | | 3 | V["foo", 12, 3] |
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// | | | 4 | V["meh", 4, 3] |
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// |-------+----------------------------+-------+----------------------------+
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// | [1]: Encoded as an offset into the value table and a length. Specified |
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// | as V[string, offset, length] for clarity. |
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// +-------------------------------------------------------------------------+
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// | * Note: Tables are laid out sequentially in memory, but displayed |
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// | here side-by-side for clarity. |
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// +-------------------------------------------------------------------------+
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//
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// +-------------------------------------------------------------------------+
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// | Value strings: |
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// +--------+----------------------------------------------------------------+
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// | Offset | Value |
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// +--------+----------------------------------------------------------------+
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// | 0 | hem\0 |
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// | 4 | meh\0 |
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// | 8 | b\0 |
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// | 10 | a\0 |
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// | 12 | foo\0 |
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// +--------+----------------------------------------------------------------+
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struct Header {
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// The number of entries in this map.
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uint32_t mEntryCount;
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// The StringTable data block for preference name strings, which act as keys
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// in the map.
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DataBlock mKeyStrings;
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// The int32_t arrays of user and default int preference values. Entries in
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// the map store their values as indices into these arrays.
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DataBlock mUserIntValues;
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DataBlock mDefaultIntValues;
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// The StringTableEntry arrays of user and default string preference values.
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//
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// Strings are stored as StringTableEntry structs with character offsets
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// into the mValueStrings string table and their corresponding lenghts.
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//
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// Entries in the map, likewise, store their string values as indices into
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// these arrays.
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DataBlock mUserStringValues;
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DataBlock mDefaultStringValues;
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// The StringTable data block for string preference values, referenced by
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// the above two data blocks.
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DataBlock mValueStrings;
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};
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using StringTableEntry = mozilla::dom::ipc::StringTableEntry;
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// Represents a preference value, as either a pair of boolean values, or an
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// index into one of the above value arrays.
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union Value {
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Value(bool aDefaultValue, bool aUserValue)
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: mDefaultBool(aDefaultValue), mUserBool(aUserValue) {}
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MOZ_IMPLICIT Value(uint16_t aIndex) : mIndex(aIndex) {}
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// The index of this entry in the value arrays.
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//
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// User and default preference values have the same indices in their
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// respective arrays. However, entries without a user value are not
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// guaranteed to have space allocated for them in the user value array, and
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// likewise for preferences without default values in the default value
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// array. This means that callers must only access value entries for entries
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// which claim to have a value of that type.
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uint16_t mIndex;
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struct {
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bool mDefaultBool;
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bool mUserBool;
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};
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};
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// Represents a preference entry in the map, containing its name, type info,
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// flags, and a reference to its value.
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struct Entry {
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// A pointer to the preference name in the KeyTable string table.
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StringTableEntry mKey;
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// The preference's value, either as a pair of booleans, or an index into
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// the value arrays. Please see the documentation for the Value struct
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// above.
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Value mValue;
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// The preference's type, as a PrefType enum value. This must *never* be
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// PrefType::None for values in a shared array.
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uint8_t mType : 2;
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// True if the preference has a default value. Callers must not attempt to
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// access the entry's default value if this is false.
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uint8_t mHasDefaultValue : 1;
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// True if the preference has a user value. Callers must not attempt to
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// access the entry's user value if this is false.
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uint8_t mHasUserValue : 1;
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// True if the preference is sticky, as defined by the preference service.
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uint8_t mIsSticky : 1;
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// True if the preference is locked, as defined by the preference service.
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uint8_t mIsLocked : 1;
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// True if the preference should be skipped while iterating over the
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// SharedPrefMap. This is used to internally store Once StaticPrefs.
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// This property is not visible to users the way sticky and locked are.
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uint8_t mIsSkippedByIteration : 1;
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};
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public:
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NS_INLINE_DECL_REFCOUNTING(SharedPrefMap)
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// A temporary wrapper class for accessing entries in the array. Instances of
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// this class are valid as long as SharedPrefMap instance is alive, but
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// generally should not be stored long term, or allocated on the heap.
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//
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// The class is implemented as two pointers, one to the SharedPrefMap
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// instance, and one to the Entry that corresponds to the preference, and is
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// meant to be cheaply returned by value from preference lookups and
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// iterators. All property accessors lazily fetch the appropriate values from
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// the shared memory region.
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class MOZ_STACK_CLASS Pref final {
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public:
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const char* Name() const { return mMap->KeyTable().GetBare(mEntry->mKey); }
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nsCString NameString() const { return mMap->KeyTable().Get(mEntry->mKey); }
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PrefType Type() const {
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MOZ_ASSERT(PrefType(mEntry->mType) != PrefType::None);
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return PrefType(mEntry->mType);
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}
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bool HasDefaultValue() const { return mEntry->mHasDefaultValue; }
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bool HasUserValue() const { return mEntry->mHasUserValue; }
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bool IsLocked() const { return mEntry->mIsLocked; }
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bool IsSticky() const { return mEntry->mIsSticky; }
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bool IsSkippedByIteration() const { return mEntry->mIsSkippedByIteration; }
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bool GetBoolValue(PrefValueKind aKind = PrefValueKind::User) const {
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MOZ_ASSERT(Type() == PrefType::Bool);
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MOZ_ASSERT(aKind == PrefValueKind::Default ? HasDefaultValue()
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: HasUserValue());
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return aKind == PrefValueKind::Default ? mEntry->mValue.mDefaultBool
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: mEntry->mValue.mUserBool;
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}
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int32_t GetIntValue(PrefValueKind aKind = PrefValueKind::User) const {
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MOZ_ASSERT(Type() == PrefType::Int);
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MOZ_ASSERT(aKind == PrefValueKind::Default ? HasDefaultValue()
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: HasUserValue());
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return aKind == PrefValueKind::Default
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? mMap->DefaultIntValues()[mEntry->mValue.mIndex]
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: mMap->UserIntValues()[mEntry->mValue.mIndex];
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}
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private:
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const StringTableEntry& GetStringEntry(PrefValueKind aKind) const {
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MOZ_ASSERT(Type() == PrefType::String);
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MOZ_ASSERT(aKind == PrefValueKind::Default ? HasDefaultValue()
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: HasUserValue());
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return aKind == PrefValueKind::Default
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? mMap->DefaultStringValues()[mEntry->mValue.mIndex]
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: mMap->UserStringValues()[mEntry->mValue.mIndex];
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}
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public:
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nsCString GetStringValue(PrefValueKind aKind = PrefValueKind::User) const {
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return mMap->ValueTable().Get(GetStringEntry(aKind));
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}
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const char* GetBareStringValue(
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PrefValueKind aKind = PrefValueKind::User) const {
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return mMap->ValueTable().GetBare(GetStringEntry(aKind));
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}
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// Returns the entry's index in the map, as understood by GetKeyAt() and
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// GetValueAt().
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size_t Index() const { return mEntry - mMap->Entries().get(); }
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bool operator==(const Pref& aPref) const { return mEntry == aPref.mEntry; }
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bool operator!=(const Pref& aPref) const { return !(*this == aPref); }
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// This is odd, but necessary in order for the C++ range iterator protocol
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// to work here.
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Pref& operator*() { return *this; }
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// Updates this wrapper to point to the next visible entry in the map. This
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// should not be attempted unless Index() is less than the map's Count().
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Pref& operator++() {
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do {
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mEntry++;
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} while (mEntry->mIsSkippedByIteration && Index() < mMap->Count());
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return *this;
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}
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Pref(const Pref& aPref) = default;
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protected:
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friend class SharedPrefMap;
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Pref(const SharedPrefMap* aPrefMap, const Entry* aEntry)
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: mMap(aPrefMap), mEntry(aEntry) {}
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private:
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const SharedPrefMap* const mMap;
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const Entry* mEntry;
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};
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// Note: These constructors are infallible, because the preference database is
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// critical to platform functionality, and we cannot operate without it.
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SharedPrefMap(const FileDescriptor&, size_t);
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explicit SharedPrefMap(SharedPrefMapBuilder&&);
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// Searches for the given preference in the map, and returns true if it
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// exists.
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bool Has(const char* aKey) const;
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bool Has(const nsCString& aKey) const { return Has(aKey.get()); }
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// Searches for the given preference in the map, and if it exists, returns
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// a Some<Pref> containing its details.
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Maybe<const Pref> Get(const char* aKey) const;
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Maybe<const Pref> Get(const nsCString& aKey) const { return Get(aKey.get()); }
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private:
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// Searches for an entry for the given key. If found, returns true, and
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// places its index in the entry array in aIndex.
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bool Find(const char* aKey, size_t* aIndex) const;
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public:
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// Returns the number of entries in the map.
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uint32_t Count() const { return EntryCount(); }
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// Returns the string entry at the given index. Keys are guaranteed to be
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// sorted lexicographically.
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//
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// The given index *must* be less than the value returned by Count().
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//
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// The returned value is a literal string which references the mapped memory
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// region.
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nsCString GetKeyAt(uint32_t aIndex) const {
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MOZ_ASSERT(aIndex < Count());
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return KeyTable().Get(Entries()[aIndex].mKey);
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}
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// Returns the value for the entry at the given index.
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//
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// The given index *must* be less than the value returned by Count().
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//
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// The returned value is valid for the lifetime of this map instance.
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const Pref GetValueAt(uint32_t aIndex) const {
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MOZ_ASSERT(aIndex < Count());
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return UncheckedGetValueAt(aIndex);
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}
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private:
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// Returns a wrapper with a pointer to an entry without checking its bounds.
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|
// This should only be used by range iterators, to check their end positions.
|
|
//
|
|
// Note: In debug builds, the RangePtr returned by entries will still assert
|
|
// that aIndex is no more than 1 past the last element in the array, since it
|
|
// also takes into account the ranged iteration use case.
|
|
Pref UncheckedGetValueAt(uint32_t aIndex) const {
|
|
return {this, (Entries() + aIndex).get()};
|
|
}
|
|
|
|
public:
|
|
// C++ range iterator protocol. begin() and end() return references to the
|
|
// first (non-skippable) and last entries in the array. The begin wrapper
|
|
// can be incremented until it matches the last element in the array, at which
|
|
// point it becomes invalid and the iteration is over.
|
|
Pref begin() const {
|
|
for (uint32_t aIndex = 0; aIndex < Count(); aIndex++) {
|
|
Pref pref = UncheckedGetValueAt(aIndex);
|
|
if (!pref.IsSkippedByIteration()) {
|
|
return pref;
|
|
}
|
|
}
|
|
return end();
|
|
}
|
|
Pref end() const { return UncheckedGetValueAt(Count()); }
|
|
|
|
// A cosmetic helper for range iteration. Returns a reference value from a
|
|
// pointer to this instance so that its .begin() and .end() methods can be
|
|
// accessed in a ranged for loop. `map->Iter()` is equivalent to `*map`, but
|
|
// makes its purpose slightly clearer.
|
|
const SharedPrefMap& Iter() const { return *this; }
|
|
|
|
// Returns a copy of the read-only file descriptor which backs the shared
|
|
// memory region for this map. The file descriptor may be passed between
|
|
// processes, and used to construct new instances of SharedPrefMap with
|
|
// the same data as this instance.
|
|
FileDescriptor CloneFileDescriptor() const;
|
|
|
|
// Returns the size of the mapped memory region. This size must be passed to
|
|
// the constructor when mapping the shared region in another process.
|
|
size_t MapSize() const { return mMap.size(); }
|
|
|
|
protected:
|
|
~SharedPrefMap() = default;
|
|
|
|
private:
|
|
template <typename T>
|
|
using StringTable = mozilla::dom::ipc::StringTable<T>;
|
|
|
|
// Type-safe getters for values in the shared memory region:
|
|
const Header& GetHeader() const { return mMap.get<Header>()[0]; }
|
|
|
|
RangedPtr<const Entry> Entries() const {
|
|
return {reinterpret_cast<const Entry*>(&GetHeader() + 1), EntryCount()};
|
|
}
|
|
|
|
uint32_t EntryCount() const { return GetHeader().mEntryCount; }
|
|
|
|
template <typename T>
|
|
RangedPtr<const T> GetBlock(const DataBlock& aBlock) const {
|
|
return RangedPtr<uint8_t>(&mMap.get<uint8_t>()[aBlock.mOffset],
|
|
aBlock.mSize)
|
|
.ReinterpretCast<const T>();
|
|
}
|
|
|
|
RangedPtr<const int32_t> DefaultIntValues() const {
|
|
return GetBlock<int32_t>(GetHeader().mDefaultIntValues);
|
|
}
|
|
RangedPtr<const int32_t> UserIntValues() const {
|
|
return GetBlock<int32_t>(GetHeader().mUserIntValues);
|
|
}
|
|
|
|
RangedPtr<const StringTableEntry> DefaultStringValues() const {
|
|
return GetBlock<StringTableEntry>(GetHeader().mDefaultStringValues);
|
|
}
|
|
RangedPtr<const StringTableEntry> UserStringValues() const {
|
|
return GetBlock<StringTableEntry>(GetHeader().mUserStringValues);
|
|
}
|
|
|
|
StringTable<nsCString> KeyTable() const {
|
|
auto& block = GetHeader().mKeyStrings;
|
|
return {{&mMap.get<uint8_t>()[block.mOffset], block.mSize}};
|
|
}
|
|
|
|
StringTable<nsCString> ValueTable() const {
|
|
auto& block = GetHeader().mValueStrings;
|
|
return {{&mMap.get<uint8_t>()[block.mOffset], block.mSize}};
|
|
}
|
|
|
|
loader::AutoMemMap mMap;
|
|
};
|
|
|
|
// A helper class which builds the contiguous look-up table used by
|
|
// SharedPrefMap. Each preference in the final map is added to the builder,
|
|
// before it is finalized and transformed into a read-only snapshot.
|
|
class MOZ_RAII SharedPrefMapBuilder {
|
|
public:
|
|
SharedPrefMapBuilder() = default;
|
|
|
|
// The set of flags for the preference, as documented in SharedPrefMap::Entry.
|
|
struct Flags {
|
|
uint8_t mHasDefaultValue : 1;
|
|
uint8_t mHasUserValue : 1;
|
|
uint8_t mIsSticky : 1;
|
|
uint8_t mIsLocked : 1;
|
|
uint8_t mIsSkippedByIteration : 1;
|
|
};
|
|
|
|
void Add(const char* aKey, const Flags& aFlags, bool aDefaultValue,
|
|
bool aUserValue);
|
|
|
|
void Add(const char* aKey, const Flags& aFlags, int32_t aDefaultValue,
|
|
int32_t aUserValue);
|
|
|
|
void Add(const char* aKey, const Flags& aFlags,
|
|
const nsCString& aDefaultValue, const nsCString& aUserValue);
|
|
|
|
// Finalizes the binary representation of the map, writes it to a shared
|
|
// memory region, and then initializes the given AutoMemMap with a reference
|
|
// to the read-only copy of it.
|
|
//
|
|
// This should generally not be used directly by callers. The
|
|
// SharedPrefMapBuilder instance should instead be passed to the SharedPrefMap
|
|
// constructor as a move reference.
|
|
Result<Ok, nsresult> Finalize(loader::AutoMemMap& aMap);
|
|
|
|
private:
|
|
using StringTableEntry = mozilla::dom::ipc::StringTableEntry;
|
|
template <typename T, typename U>
|
|
using StringTableBuilder = mozilla::dom::ipc::StringTableBuilder<T, U>;
|
|
|
|
// An opaque descriptor of the index of a preference entry in a value array,
|
|
// which can be converted numeric index after the ValueTableBuilder is
|
|
// finalized.
|
|
struct ValueIdx {
|
|
// The relative index of the entry, based on its class. Entries for
|
|
// preferences with user values appear at the value arrays. Entries with
|
|
// only default values begin after the last entry with a user value.
|
|
uint16_t mIndex;
|
|
bool mHasUserValue;
|
|
};
|
|
|
|
// A helper class for building default and user value arrays for preferences.
|
|
//
|
|
// As described in the SharedPrefMap class, this helper optimizes the way that
|
|
// it builds its value arrays, in that:
|
|
//
|
|
// - It stores value entries for all preferences with user values before
|
|
// entries for preferences with only default values, and allocates no
|
|
// entries for preferences with only default values in the user value array.
|
|
// Since most preferences have only default values, this dramatically
|
|
// reduces the space required for value storage.
|
|
//
|
|
// - For preferences with only default values, it de-duplicates value entries,
|
|
// and returns the same indices for all preferences with the same value.
|
|
//
|
|
// One important complication of this approach is that it means we cannot know
|
|
// the final index of any entry with only a default value until all entries
|
|
// have been added to the builder, since it depends on the final number of
|
|
// user entries in the output.
|
|
//
|
|
// To deal with this, when entries are added, we return an opaque ValueIndex
|
|
// struct, from which we can calculate the final index after the map has been
|
|
// finalized.
|
|
template <typename HashKey, typename ValueType_>
|
|
class ValueTableBuilder {
|
|
public:
|
|
using ValueType = ValueType_;
|
|
|
|
// Adds an entry for a preference with only a default value to the array,
|
|
// and returns an opaque descriptor for its index.
|
|
ValueIdx Add(const ValueType& aDefaultValue) {
|
|
auto index = uint16_t(mDefaultEntries.Count());
|
|
|
|
auto entry = mDefaultEntries.LookupForAdd(aDefaultValue).OrInsert([&]() {
|
|
return Entry{index, false, aDefaultValue};
|
|
});
|
|
|
|
return {entry.mIndex, false};
|
|
}
|
|
|
|
// Adds an entry for a preference with a user value to the array. Regardless
|
|
// of whether the preference has a default value, space must be allocated
|
|
// for it. For preferences with no default value, the actual value which
|
|
// appears in the array at its value index is ignored.
|
|
ValueIdx Add(const ValueType& aDefaultValue, const ValueType& aUserValue) {
|
|
auto index = uint16_t(mUserEntries.Length());
|
|
|
|
mUserEntries.AppendElement(Entry{index, true, aDefaultValue, aUserValue});
|
|
|
|
return {index, true};
|
|
}
|
|
|
|
// Returns the final index for an entry based on its opaque index
|
|
// descriptor. This must only be called after the caller has finished adding
|
|
// entries to the builder.
|
|
uint16_t GetIndex(const ValueIdx& aIndex) const {
|
|
uint16_t base = aIndex.mHasUserValue ? 0 : UserCount();
|
|
return base + aIndex.mIndex;
|
|
}
|
|
|
|
// Writes out the array of default values at the block beginning at the
|
|
// given pointer. The block must be at least as large as the value returned
|
|
// by DefaultSize().
|
|
void WriteDefaultValues(const RangedPtr<uint8_t>& aBuffer) const {
|
|
auto buffer = aBuffer.ReinterpretCast<ValueType>();
|
|
|
|
for (const auto& entry : mUserEntries) {
|
|
buffer[entry.mIndex] = entry.mDefaultValue;
|
|
}
|
|
|
|
size_t defaultsOffset = UserCount();
|
|
for (auto iter = mDefaultEntries.ConstIter(); !iter.Done(); iter.Next()) {
|
|
const auto& entry = iter.Data();
|
|
buffer[defaultsOffset + entry.mIndex] = entry.mDefaultValue;
|
|
}
|
|
}
|
|
|
|
// Writes out the array of user values at the block beginning at the
|
|
// given pointer. The block must be at least as large as the value returned
|
|
// by UserSize().
|
|
void WriteUserValues(const RangedPtr<uint8_t>& aBuffer) const {
|
|
auto buffer = aBuffer.ReinterpretCast<ValueType>();
|
|
|
|
for (const auto& entry : mUserEntries) {
|
|
buffer[entry.mIndex] = entry.mUserValue;
|
|
}
|
|
}
|
|
|
|
// These return the number of entries in the default and user value arrays,
|
|
// respectively.
|
|
uint32_t DefaultCount() const {
|
|
return UserCount() + mDefaultEntries.Count();
|
|
}
|
|
uint32_t UserCount() const { return mUserEntries.Length(); }
|
|
|
|
// These return the byte sizes of the default and user value arrays,
|
|
// respectively.
|
|
uint32_t DefaultSize() const { return DefaultCount() * sizeof(ValueType); }
|
|
uint32_t UserSize() const { return UserCount() * sizeof(ValueType); }
|
|
|
|
void Clear() {
|
|
mUserEntries.Clear();
|
|
mDefaultEntries.Clear();
|
|
}
|
|
|
|
static constexpr size_t Alignment() { return alignof(ValueType); }
|
|
|
|
private:
|
|
struct Entry {
|
|
uint16_t mIndex;
|
|
bool mHasUserValue;
|
|
ValueType mDefaultValue;
|
|
ValueType mUserValue{};
|
|
};
|
|
|
|
AutoTArray<Entry, 256> mUserEntries;
|
|
|
|
nsDataHashtable<HashKey, Entry> mDefaultEntries;
|
|
};
|
|
|
|
// A special-purpose string table builder for keys which are already
|
|
// guaranteed to be unique. Duplicate values will not be detected or
|
|
// de-duplicated.
|
|
template <typename CharType>
|
|
class UniqueStringTableBuilder {
|
|
public:
|
|
using ElemType = CharType;
|
|
|
|
explicit UniqueStringTableBuilder(size_t aCapacity) : mEntries(aCapacity) {}
|
|
|
|
StringTableEntry Add(const CharType* aKey) {
|
|
auto entry =
|
|
mEntries.AppendElement(Entry{mSize, uint32_t(strlen(aKey)), aKey});
|
|
|
|
mSize += entry->mLength + 1;
|
|
|
|
return {entry->mOffset, entry->mLength};
|
|
}
|
|
|
|
void Write(const RangedPtr<uint8_t>& aBuffer) {
|
|
auto buffer = aBuffer.ReinterpretCast<ElemType>();
|
|
|
|
for (auto& entry : mEntries) {
|
|
memcpy(&buffer[entry.mOffset], entry.mValue,
|
|
sizeof(ElemType) * (entry.mLength + 1));
|
|
}
|
|
}
|
|
|
|
uint32_t Count() const { return mEntries.Length(); }
|
|
|
|
uint32_t Size() const { return mSize * sizeof(ElemType); }
|
|
|
|
void Clear() { mEntries.Clear(); }
|
|
|
|
static constexpr size_t Alignment() { return alignof(ElemType); }
|
|
|
|
private:
|
|
struct Entry {
|
|
uint32_t mOffset;
|
|
uint32_t mLength;
|
|
const CharType* mValue;
|
|
};
|
|
|
|
nsTArray<Entry> mEntries;
|
|
uint32_t mSize = 0;
|
|
};
|
|
|
|
// A preference value entry, roughly corresponding to the
|
|
// SharedPrefMap::Value struct, but with a temporary place-holder value rather
|
|
// than a final value index.
|
|
union Value {
|
|
Value(bool aDefaultValue, bool aUserValue)
|
|
: mDefaultBool(aDefaultValue), mUserBool(aUserValue) {}
|
|
|
|
MOZ_IMPLICIT Value(const ValueIdx& aIndex) : mIndex(aIndex) {}
|
|
|
|
// For Bool preferences, their default and user bool values.
|
|
struct {
|
|
bool mDefaultBool;
|
|
bool mUserBool;
|
|
};
|
|
// For Int and String preferences, an opaque descriptor for their entries in
|
|
// their value arrays. This must be passed to the appropriate
|
|
// ValueTableBuilder to obtain the final index when the entry is serialized.
|
|
ValueIdx mIndex;
|
|
};
|
|
|
|
// A preference entry, to be converted to a SharedPrefMap::Entry struct during
|
|
// serialization.
|
|
struct Entry {
|
|
// The entry's preference name, as passed to Add(). The caller is
|
|
// responsible for keeping this pointer alive until the builder is
|
|
// finalized.
|
|
const char* mKeyString;
|
|
// The entry in mKeyTable corresponding to mKeyString.
|
|
StringTableEntry mKey;
|
|
Value mValue;
|
|
|
|
uint8_t mType : 2;
|
|
uint8_t mHasDefaultValue : 1;
|
|
uint8_t mHasUserValue : 1;
|
|
uint8_t mIsSticky : 1;
|
|
uint8_t mIsLocked : 1;
|
|
uint8_t mIsSkippedByIteration : 1;
|
|
};
|
|
|
|
// Converts a builder Value struct to a SharedPrefMap::Value struct for
|
|
// serialization. This must not be called before callers have finished adding
|
|
// entries to the value array builders.
|
|
SharedPrefMap::Value GetValue(const Entry& aEntry) const {
|
|
switch (PrefType(aEntry.mType)) {
|
|
case PrefType::Bool:
|
|
return {aEntry.mValue.mDefaultBool, aEntry.mValue.mUserBool};
|
|
case PrefType::Int:
|
|
return {mIntValueTable.GetIndex(aEntry.mValue.mIndex)};
|
|
case PrefType::String:
|
|
return {mStringValueTable.GetIndex(aEntry.mValue.mIndex)};
|
|
default:
|
|
MOZ_ASSERT_UNREACHABLE("Invalid pref type");
|
|
return {false, false};
|
|
}
|
|
}
|
|
|
|
UniqueStringTableBuilder<char> mKeyTable{kExpectedPrefCount};
|
|
StringTableBuilder<nsCStringHashKey, nsCString> mValueStringTable;
|
|
|
|
ValueTableBuilder<nsUint32HashKey, uint32_t> mIntValueTable;
|
|
ValueTableBuilder<nsGenericHashKey<StringTableEntry>, StringTableEntry>
|
|
mStringValueTable;
|
|
|
|
nsTArray<Entry> mEntries{kExpectedPrefCount};
|
|
};
|
|
|
|
} // namespace mozilla
|
|
|
|
#endif // dom_ipc_SharedPrefMap_h
|