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Depends on D137612 Differential Revision: https://phabricator.services.mozilla.com/D137650
95 lines
3.7 KiB
ReStructuredText
95 lines
3.7 KiB
ReStructuredText
The chapter describes the NSPR API for named shared memory. Shared
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memory allows multiple processes to access one or more common shared
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memory regions, using it as an interprocess communication channel. The
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NSPR shared memory API provides a cross-platform named shared-memory
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interface that is modeled on similar constructs in the Unix and Windows
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operating systems.
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- `Shared Memory Protocol <#Shared_Memory_Protocol>`__
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- `Named Shared Memory Functions <#Named_Shared_Memory_Functions>`__
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.. _Shared_Memory_Protocol:
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Shared Memory Protocol
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----------------------
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.. _Using_Named_Shared_Memory_Functions:
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Using Named Shared Memory Functions
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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:ref:`PR_OpenSharedMemory` creates the shared memory segment, if it does
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not already exist, or opens a connection with the existing shared memory
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segment if it already exists.
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:ref:`PR_AttachSharedMemory` should be called following
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:ref:`PR_OpenSharedMemory` to map the memory segment to an address in the
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application's address space. :ref:`PR_AttachSharedMemory` may also be
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called to remap a shared memory segment after detaching the same
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``PRSharedMemory`` object. Be sure to detach it when you're finished.
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:ref:`PR_DetachSharedMemory` should be called to unmap the shared memory
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segment from the application's address space.
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:ref:`PR_CloseSharedMemory` should be called when no further use of the
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``PRSharedMemory`` object is required within a process. Following a call
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to :ref:`PR_CloseSharedMemory`, the ``PRSharedMemory`` object is invalid
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and cannot be reused.
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:ref:`PR_DeleteSharedMemory` should be called before process termination.
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After you call :ref:`PR_DeleteSharedMemory`, any further use of the shared
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memory associated with the name may cause unpredictable results.
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Filenames
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~~~~~~~~~
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The name passed to :ref:`PR_OpenSharedMemory` should be a valid filename
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for a Unix platform. :ref:`PR_OpenSharedMemory` creates file using the name
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passed in. Some platforms may mangle the name before creating the file
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and the shared memory. The Unix implementation may use SysV IPC shared
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memory, Posix shared memory, or memory mapped files; the filename may be
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used to define the namespace. On Windows, the name is significant, but
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there is no file associated with the name.
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No assumptions about the persistence of data in the named file should be
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made. Depending on platform, the shared memory may be mapped onto system
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paging space and be discarded at process termination.
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All names provided to :ref:`PR_OpenSharedMemory` should be valid filename
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syntax or name syntax for shared memory for the target platform.
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Referenced directories should have permissions appropriate for writing.
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.. _Limits_on_Shared_Memory_Resources:
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Limits on Shared Memory Resources
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~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Different platforms have limits on both the number and size of shared
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memory resources. The default system limits on some platforms may be
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smaller than your requirements. These limits may be adjusted on some
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platforms either via boot-time options or by setting the size of the
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system paging space to accommodate more and/or larger shared memory
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segment(s).
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.. _Security_Considerations:
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Security Considerations
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~~~~~~~~~~~~~~~~~~~~~~~
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On Unix platforms, depending on implementation, contents of the backing
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store for the shared memory can be exposed via the file system. Set
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permissions and or access controls at create and attach time to ensure
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you get the desired security.
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On Windows platforms, no special security measures are provided.
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.. _Named_Shared_Memory_Functions:
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Named Shared Memory Functions
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-----------------------------
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- :ref:`PR_OpenSharedMemory`
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- :ref:`PR_AttachSharedMemory`
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- :ref:`PR_DetachSharedMemory`
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- :ref:`PR_CloseSharedMemory`
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- :ref:`PR_DeleteSharedMemory`
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