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315 lines
8.6 KiB
C++
315 lines
8.6 KiB
C++
/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
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* vim: sw=2 ts=8 et :
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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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#ifndef mozilla_ipc_Shmem_h
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#define mozilla_ipc_Shmem_h
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#include "mozilla/Attributes.h"
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#include "base/basictypes.h"
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#include "base/process.h"
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#include "nscore.h"
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#include "nsDebug.h"
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#include "nsAutoPtr.h"
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#include "ipc/IPCMessageUtils.h"
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#include "mozilla/ipc/SharedMemory.h"
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/**
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* |Shmem| is one agent in the IPDL shared memory scheme. The way it
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works is essentially
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*
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* (1) C++ code calls, say, |parentActor->AllocShmem(size)|
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* (2) IPDL-generated code creates a |mozilla::ipc::SharedMemory|
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* wrapping the bare OS shmem primitives. The code then adds the new
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* SharedMemory to the set of shmem segments being managed by IPDL.
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*
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* (3) IPDL-generated code "shares" the new SharedMemory to the child
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* process, and then sends a special asynchronous IPC message to the
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* child notifying it of the creation of the segment. (What this
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* means is OS specific.)
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*
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* (4a) The child receives the special IPC message, and using the
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* |SharedMemory{SysV,Basic}::Handle| it was passed, creates a
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* |mozilla::ipc::SharedMemory| in the child
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* process.
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*
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* (4b) After sending the "shmem-created" IPC message, IPDL-generated
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* code in the parent returns a |mozilla::ipc::Shmem| back to the C++
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* caller of |parentActor->AllocShmem()|. The |Shmem| is a "weak
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* reference" to the underlying |SharedMemory|, which is managed by
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* IPDL-generated code. C++ consumers of |Shmem| can't get at the
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* underlying |SharedMemory|.
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*
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* If parent code wants to give access rights to the Shmem to the
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* child, it does so by sending its |Shmem| to the child, in an IPDL
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* message. The parent's |Shmem| then "dies", i.e. becomes
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* inaccessible. This process could be compared to passing a
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* "shmem-access baton" between parent and child.
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*/
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namespace mozilla {
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namespace layers {
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class ShadowLayerForwarder;
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}
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namespace ipc {
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class Shmem MOZ_FINAL
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{
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friend struct IPC::ParamTraits<mozilla::ipc::Shmem>;
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#ifdef DEBUG
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// For ShadowLayerForwarder::CheckSurfaceDescriptor
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friend class mozilla::layers::ShadowLayerForwarder;
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#endif
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public:
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typedef int32_t id_t;
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// Low-level wrapper around platform shmem primitives.
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typedef mozilla::ipc::SharedMemory SharedMemory;
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typedef SharedMemory::SharedMemoryType SharedMemoryType;
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struct IHadBetterBeIPDLCodeCallingThis_OtherwiseIAmADoodyhead {};
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Shmem() :
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mSegment(nullptr),
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mData(nullptr),
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mSize(0),
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mId(0)
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{
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}
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Shmem(const Shmem& aOther) :
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mSegment(aOther.mSegment),
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mData(aOther.mData),
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mSize(aOther.mSize),
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mId(aOther.mId)
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{
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}
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#if !defined(DEBUG)
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Shmem(IHadBetterBeIPDLCodeCallingThis_OtherwiseIAmADoodyhead,
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SharedMemory* aSegment, id_t aId) :
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mSegment(aSegment),
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mData(aSegment->memory()),
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mSize(0),
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mId(aId)
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{
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mSize = static_cast<size_t>(*PtrToSize(mSegment));
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}
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#else
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Shmem(IHadBetterBeIPDLCodeCallingThis_OtherwiseIAmADoodyhead,
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SharedMemory* aSegment, id_t aId);
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#endif
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~Shmem()
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{
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// Shmem only holds a "weak ref" to the actual segment, which is
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// owned by IPDL. So there's nothing interesting to be done here
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forget(IHadBetterBeIPDLCodeCallingThis_OtherwiseIAmADoodyhead());
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}
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Shmem& operator=(const Shmem& aRhs)
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{
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mSegment = aRhs.mSegment;
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mData = aRhs.mData;
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mSize = aRhs.mSize;
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mId = aRhs.mId;
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return *this;
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}
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bool operator==(const Shmem& aRhs) const
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{
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// need to compare IDs because of AdoptShmem(); two Shmems might
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// refer to the same segment but with different IDs for different
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// protocol trees. (NB: it's possible for this method to
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// spuriously return true if AdoptShmem() gives the same ID for
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// two protocol trees, but I don't think that can cause any
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// problems since the Shmems really would be indistinguishable.)
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return mSegment == aRhs.mSegment && mId == aRhs.mId;
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}
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// Returns whether this Shmem is writable by you, and thus whether you can
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// transfer writability to another actor.
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bool
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IsWritable() const
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{
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return mSegment != nullptr;
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}
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// Returns whether this Shmem is readable by you, and thus whether you can
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// transfer readability to another actor.
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bool
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IsReadable() const
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{
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return mSegment != nullptr;
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}
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// Return a pointer to the user-visible data segment.
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template<typename T>
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T*
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get() const
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{
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AssertInvariants();
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AssertAligned<T>();
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return reinterpret_cast<T*>(mData);
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}
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// Return the size of the segment as requested when this shmem
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// segment was allocated, in units of T. The underlying mapping may
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// actually be larger because of page alignment and private data,
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// but this isn't exposed to clients.
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template<typename T>
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size_t
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Size() const
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{
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AssertInvariants();
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AssertAligned<T>();
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return mSize / sizeof(T);
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}
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int GetSysVID() const;
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// These shouldn't be used directly, use the IPDL interface instead.
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id_t Id(IHadBetterBeIPDLCodeCallingThis_OtherwiseIAmADoodyhead) const {
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return mId;
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}
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SharedMemory* Segment(IHadBetterBeIPDLCodeCallingThis_OtherwiseIAmADoodyhead) const {
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return mSegment;
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}
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#ifndef DEBUG
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void RevokeRights(IHadBetterBeIPDLCodeCallingThis_OtherwiseIAmADoodyhead)
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{
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}
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#else
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void RevokeRights(IHadBetterBeIPDLCodeCallingThis_OtherwiseIAmADoodyhead);
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#endif
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void forget(IHadBetterBeIPDLCodeCallingThis_OtherwiseIAmADoodyhead)
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{
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mSegment = nullptr;
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mData = nullptr;
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mSize = 0;
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mId = 0;
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}
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static already_AddRefed<Shmem::SharedMemory>
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Alloc(IHadBetterBeIPDLCodeCallingThis_OtherwiseIAmADoodyhead,
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size_t aNBytes,
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SharedMemoryType aType,
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bool aUnsafe,
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bool aProtect=false);
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// Prepare this to be shared with |aProcess|. Return an IPC message
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// that contains enough information for the other process to map
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// this segment in OpenExisting() below. Return a new message if
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// successful (owned by the caller), nullptr if not.
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IPC::Message*
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ShareTo(IHadBetterBeIPDLCodeCallingThis_OtherwiseIAmADoodyhead,
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base::ProcessHandle aProcess,
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int32_t routingId);
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// Stop sharing this with |aProcess|. Return an IPC message that
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// contains enough information for the other process to unmap this
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// segment. Return a new message if successful (owned by the
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// caller), nullptr if not.
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IPC::Message*
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UnshareFrom(IHadBetterBeIPDLCodeCallingThis_OtherwiseIAmADoodyhead,
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base::ProcessHandle aProcess,
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int32_t routingId);
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// Return a SharedMemory instance in this process using the
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// descriptor shared to us by the process that created the
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// underlying OS shmem resource. The contents of the descriptor
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// depend on the type of SharedMemory that was passed to us.
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static already_AddRefed<SharedMemory>
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OpenExisting(IHadBetterBeIPDLCodeCallingThis_OtherwiseIAmADoodyhead,
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const IPC::Message& aDescriptor,
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id_t* aId,
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bool aProtect=false);
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static void
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Dealloc(IHadBetterBeIPDLCodeCallingThis_OtherwiseIAmADoodyhead,
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SharedMemory* aSegment);
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private:
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template<typename T>
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void AssertAligned() const
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{
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if (0 != (mSize % sizeof(T)))
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NS_RUNTIMEABORT("shmem is not T-aligned");
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}
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#if !defined(DEBUG)
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void AssertInvariants() const
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{ }
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static uint32_t*
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PtrToSize(SharedMemory* aSegment)
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{
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char* endOfSegment =
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reinterpret_cast<char*>(aSegment->memory()) + aSegment->Size();
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return reinterpret_cast<uint32_t*>(endOfSegment - sizeof(uint32_t));
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}
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#else
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void AssertInvariants() const;
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#endif
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SharedMemory* MOZ_NON_OWNING_REF mSegment;
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void* mData;
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size_t mSize;
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id_t mId;
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};
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} // namespace ipc
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} // namespace mozilla
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namespace IPC {
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template<>
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struct ParamTraits<mozilla::ipc::Shmem>
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{
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typedef mozilla::ipc::Shmem paramType;
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// NB: Read()/Write() look creepy in that Shmems have a pointer
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// member, but IPDL internally uses mId to properly initialize a
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// "real" Shmem
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static void Write(Message* aMsg, const paramType& aParam)
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{
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WriteParam(aMsg, aParam.mId);
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}
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static bool Read(const Message* aMsg, void** aIter, paramType* aResult)
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{
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paramType::id_t id;
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if (!ReadParam(aMsg, aIter, &id))
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return false;
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aResult->mId = id;
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return true;
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}
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static void Log(const paramType& aParam, std::wstring* aLog)
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{
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aLog->append(L"(shmem segment)");
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}
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};
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} // namespace IPC
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#endif // ifndef mozilla_ipc_Shmem_h
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