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b9e071e2e8
Entry storage allocation now occurs on the first lookupForAdd()/put()/putNew().
This removes the need for init() and initialized(), and matches how
PLDHashTable/nsTHashtable work. It also removes the need for init() functions
in a lot of types that are built on top of mozilla::Hash{Map,Set}.
Pros:
- No need for init() calls and subsequent checks.
- No memory allocated for empty tables, which are not that uncommon.
Cons:
- An extra branch in lookup() and lookupForAdd(), but not in put()/putNew(),
because the existing checkOverloaded() can handle it.
Specifics:
- Construction now can take a length parameter.
- init() is removed. Explicit length-setting, when necessary, now occurs in the
constructors.
- initialized() is removed.
- capacity() now returns zero when the entry storage is absent.
- lookupForAdd() is no longer `const`, because it can instantiate the storage,
which requires modifications.
- lookupForAdd() can now return an invalid AddPtr in two cases:
- old: hashing failure (due to OOM in the hasher)
- new: OOM while instantiating entry storage
The existing failure handling paths for the old case work for the new case.
- clear(), finish(), and clearAndShrink() are replaced by clear(), compact(),
and reserve(). The old compactIfUnderloaded() is also removed.
- Capacity computation code is now in its own functions, bestCapacity() and
hashShift(). setTableSizeLog2() is removed.
- uint32_t is used throughout for capacities, instead of size_t, for
consistency with other similar values.
- changeTableSize() now takes a capacity instead of a deltaLog2, and it can now
handle !mTable.
Measurements:
- Total source code size is reduced by over 900 lines. Also, lots of existing
lines got shorter (i.e. two checks were reduced to one).
- Executable size barely changed, down by 2 KiB on Linux64. The extra branches
are compensated for by the lack of init() calls.
- Speed changed negligibly. The instruction count for Bench_Cpp_MozHash
increased from 2.84 billion to 2.89 billion but any execution time change was
well below noise.
95 lines
2.4 KiB
C++
95 lines
2.4 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
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* vim: set ts=4 sw=4 et tw=80:
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*
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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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#include "JavaScriptChild.h"
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#include "mozilla/dom/ContentChild.h"
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#include "mozilla/dom/BindingUtils.h"
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#include "mozilla/ipc/MessageChannel.h"
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#include "nsContentUtils.h"
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#include "xpcprivate.h"
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#include "jsfriendapi.h"
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#include "AccessCheck.h"
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using namespace JS;
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using namespace mozilla;
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using namespace mozilla::jsipc;
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using mozilla::AutoSafeJSContext;
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static void
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UpdateChildWeakPointersBeforeSweepingZoneGroup(JSContext* cx, void* data)
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{
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static_cast<JavaScriptChild*>(data)->updateWeakPointers();
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}
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static void
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TraceChild(JSTracer* trc, void* data)
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{
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static_cast<JavaScriptChild*>(data)->trace(trc);
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}
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JavaScriptChild::~JavaScriptChild()
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{
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JSContext* cx = dom::danger::GetJSContext();
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JS_RemoveWeakPointerZonesCallback(cx, UpdateChildWeakPointersBeforeSweepingZoneGroup);
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JS_RemoveExtraGCRootsTracer(cx, TraceChild, this);
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}
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bool
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JavaScriptChild::init()
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{
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JSContext* cx = dom::danger::GetJSContext();
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JS_AddWeakPointerZonesCallback(cx, UpdateChildWeakPointersBeforeSweepingZoneGroup, this);
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JS_AddExtraGCRootsTracer(cx, TraceChild, this);
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return true;
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}
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void
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JavaScriptChild::trace(JSTracer* trc)
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{
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objects_.trace(trc, strongReferenceObjIdMinimum_);
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}
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void
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JavaScriptChild::updateWeakPointers()
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{
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objects_.sweep();
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unwaivedObjectIds_.sweep();
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waivedObjectIds_.sweep();
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}
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JSObject*
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JavaScriptChild::scopeForTargetObjects()
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{
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// CPOWs from the parent need to point into the child's privileged junk
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// scope so that they can benefit from XrayWrappers in the child.
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return xpc::PrivilegedJunkScope();
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}
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mozilla::ipc::IPCResult
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JavaScriptChild::RecvDropTemporaryStrongReferences(const uint64_t& upToObjId)
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{
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strongReferenceObjIdMinimum_ = upToObjId + 1;
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return IPC_OK();
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}
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PJavaScriptChild*
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mozilla::jsipc::NewJavaScriptChild()
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{
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JavaScriptChild* child = new JavaScriptChild();
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if (!child->init()) {
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delete child;
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return nullptr;
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}
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return child;
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}
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void
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mozilla::jsipc::ReleaseJavaScriptChild(PJavaScriptChild* child)
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{
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static_cast<JavaScriptChild*>(child)->decref();
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}
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