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This is based on the SharedStringMap that's currently used for shared memory string bundles. When the parent process is ready to launch its first content process, it creates a snapshot of the current state of the preference database, maps that as read-only, and shares it with each content process. Look-ups in the snapshotted map are done entirely using data in the shared memory region. It doesn't require any additional per-process state data. MozReview-Commit-ID: BdTUhak7dmS --HG-- extra : source : 68bb03c63b3cee1d47cbddfd3abf919f5783c04b
65 lines
1.7 KiB
C++
65 lines
1.7 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*- */
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/* vim: set ts=8 sts=4 et sw=4 tw=99: */
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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_MemMapSnapshot_h
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#define dom_ipc_MemMapSnapshot_h
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#include "mozilla/AutoMemMap.h"
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#include "mozilla/Attributes.h"
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#include "mozilla/Maybe.h"
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#include "mozilla/RangedPtr.h"
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#include "mozilla/Result.h"
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#ifdef XP_WIN
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# include "mozilla/ipc/FileDescriptor.h"
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#endif
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namespace mozilla {
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namespace ipc {
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/**
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* A helper class for creating a read-only snapshot of memory-mapped data.
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*
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* The Init() method initializes a read-write memory mapped region of the given
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* size, which can be initialized with arbitrary data. The Finalize() method
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* remaps that region as read-only (and backs it with a read-only file
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* descriptor), and initializes an AutoMemMap with the new contents.
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*
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* The file descriptor for the resulting AutoMemMap can be shared among
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* processes, to safely access a shared, read-only copy of the data snapshot.
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*/
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class MOZ_RAII MemMapSnapshot
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{
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public:
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Result<Ok, nsresult> Init(size_t aSize);
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Result<Ok, nsresult> Finalize(loader::AutoMemMap& aMap);
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template<typename T = void>
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RangedPtr<T> Get()
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{
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MOZ_ASSERT(mInitialized);
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return mMem.get<T>();
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}
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private:
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Result<Ok, nsresult> Create(size_t aSize);
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Result<Ok, nsresult> Freeze(loader::AutoMemMap& aMem);
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loader::AutoMemMap mMem;
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bool mInitialized = false;
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#ifdef XP_WIN
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Maybe<FileDescriptor> mFile;
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#else
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nsCString mPath;
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#endif
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};
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} // ipc
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} // mozilla
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#endif // dom_ipc_MemMapSnapshot_h
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