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a697f87d36
The current IPC::Message constructor takes a large number of arguments, three of which--the nesting level, the priority, and the compression--are almost always constant by virtue of the vast majority of Message construction being done by auto-generated IPDL code. But then we take these constant values into the Message constructor, we check them for various values, and then based on those values, we perform a bunch of bitfield operations to store flags based on those values. This is wasted work. Furthermore, for replies to IPDL messages, we'll construct a Message object, and then call mutating setters on the Message object that will perform even more bitfield manipulations. Again, these operations are performing tasks at runtime that are the same every single time, and use information we already have at compile time. The impact of these extra operations is not large, maybe 15-30K of extra code, depending on platform. Nonetheless, we can easily make them go away, and make everything cleaner to boot. This patch adds a HeaderFlags class that encapsulates all the knowledge about the various kinds of flags Message needs to know about. We can construct HeaderFlags objects with strongly-typed enum arguments for the various kinds of flags, and the compiler can take care of folding all of those flags together into a constant when possible (and it is possible for all the IPDL-generated code that instantiates Messages). The upshot is that we do no unnecessary work in the Message constructor itself. We can also remove various mutating operations on Message, as those operations were only there to support post-constructor flag twiddling, which is no longer necessary.
499 lines
14 KiB
C++
499 lines
14 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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#include "Shmem.h"
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#include "ProtocolUtils.h"
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#include "SharedMemoryBasic.h"
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#include "mozilla/Unused.h"
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namespace mozilla {
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namespace ipc {
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class ShmemCreated : public IPC::Message
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{
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private:
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typedef Shmem::id_t id_t;
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public:
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ShmemCreated(int32_t routingId,
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id_t aIPDLId,
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size_t aSize,
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SharedMemory::SharedMemoryType aType) :
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IPC::Message(routingId, SHMEM_CREATED_MESSAGE_TYPE, 0,
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HeaderFlags(NESTED_INSIDE_CPOW))
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{
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IPC::WriteParam(this, aIPDLId);
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IPC::WriteParam(this, aSize);
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IPC::WriteParam(this, int32_t(aType));
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}
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static bool
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ReadInfo(const Message* msg, PickleIterator* iter,
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id_t* aIPDLId,
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size_t* aSize,
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SharedMemory::SharedMemoryType* aType)
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{
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if (!IPC::ReadParam(msg, iter, aIPDLId) ||
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!IPC::ReadParam(msg, iter, aSize) ||
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!IPC::ReadParam(msg, iter, reinterpret_cast<int32_t*>(aType)))
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return false;
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return true;
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}
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void Log(const std::string& aPrefix,
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FILE* aOutf) const
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{
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fputs("(special ShmemCreated msg)", aOutf);
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}
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};
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class ShmemDestroyed : public IPC::Message
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{
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private:
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typedef Shmem::id_t id_t;
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public:
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ShmemDestroyed(int32_t routingId,
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id_t aIPDLId) :
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IPC::Message(routingId, SHMEM_DESTROYED_MESSAGE_TYPE)
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{
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IPC::WriteParam(this, aIPDLId);
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}
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};
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static SharedMemory*
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NewSegment(SharedMemory::SharedMemoryType aType)
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{
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if (SharedMemory::TYPE_BASIC == aType) {
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return new SharedMemoryBasic;
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} else {
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NS_ERROR("unknown Shmem type");
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return nullptr;
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}
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}
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static already_AddRefed<SharedMemory>
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CreateSegment(SharedMemory::SharedMemoryType aType, size_t aNBytes, size_t aExtraSize)
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{
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RefPtr<SharedMemory> segment = NewSegment(aType);
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if (!segment) {
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return nullptr;
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}
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size_t size = SharedMemory::PageAlignedSize(aNBytes + aExtraSize);
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if (!segment->Create(size) || !segment->Map(size)) {
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return nullptr;
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}
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return segment.forget();
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}
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static already_AddRefed<SharedMemory>
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ReadSegment(const IPC::Message& aDescriptor, Shmem::id_t* aId, size_t* aNBytes, size_t aExtraSize)
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{
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if (SHMEM_CREATED_MESSAGE_TYPE != aDescriptor.type()) {
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NS_ERROR("expected 'shmem created' message");
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return nullptr;
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}
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SharedMemory::SharedMemoryType type;
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PickleIterator iter(aDescriptor);
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if (!ShmemCreated::ReadInfo(&aDescriptor, &iter, aId, aNBytes, &type)) {
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return nullptr;
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}
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RefPtr<SharedMemory> segment = NewSegment(type);
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if (!segment) {
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return nullptr;
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}
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if (!segment->ReadHandle(&aDescriptor, &iter)) {
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NS_ERROR("trying to open invalid handle");
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return nullptr;
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}
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aDescriptor.EndRead(iter);
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size_t size = SharedMemory::PageAlignedSize(*aNBytes + aExtraSize);
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if (!segment->Map(size)) {
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return nullptr;
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}
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// close the handle to the segment after it is mapped
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segment->CloseHandle();
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return segment.forget();
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}
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static void
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DestroySegment(SharedMemory* aSegment)
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{
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// the SharedMemory dtor closes and unmaps the actual OS shmem segment
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if (aSegment) {
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aSegment->Release();
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}
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}
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#if defined(DEBUG)
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static const char sMagic[] =
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"This little piggy went to market.\n"
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"This little piggy stayed at home.\n"
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"This little piggy has roast beef,\n"
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"This little piggy had none.\n"
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"And this little piggy cried \"Wee! Wee! Wee!\" all the way home";
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struct Header {
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// Don't use size_t or bool here because their size depends on the
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// architecture.
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uint32_t mSize;
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uint32_t mUnsafe;
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char mMagic[sizeof(sMagic)];
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};
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static void
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GetSections(Shmem::SharedMemory* aSegment,
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Header** aHeader,
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char** aFrontSentinel,
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char** aData,
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char** aBackSentinel)
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{
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MOZ_ASSERT(aSegment && aFrontSentinel && aData && aBackSentinel,
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"null param(s)");
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*aFrontSentinel = reinterpret_cast<char*>(aSegment->memory());
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MOZ_ASSERT(*aFrontSentinel, "null memory()");
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*aHeader = reinterpret_cast<Header*>(*aFrontSentinel);
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size_t pageSize = Shmem::SharedMemory::SystemPageSize();
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*aData = *aFrontSentinel + pageSize;
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*aBackSentinel = *aFrontSentinel + aSegment->Size() - pageSize;
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}
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static Header*
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GetHeader(Shmem::SharedMemory* aSegment)
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{
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Header* header;
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char* dontcare;
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GetSections(aSegment, &header, &dontcare, &dontcare, &dontcare);
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return header;
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}
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static void
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Protect(SharedMemory* aSegment)
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{
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MOZ_ASSERT(aSegment, "null segment");
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aSegment->Protect(reinterpret_cast<char*>(aSegment->memory()),
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aSegment->Size(),
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RightsNone);
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}
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static void
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Unprotect(SharedMemory* aSegment)
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{
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MOZ_ASSERT(aSegment, "null segment");
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aSegment->Protect(reinterpret_cast<char*>(aSegment->memory()),
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aSegment->Size(),
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RightsRead | RightsWrite);
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}
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//
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// In debug builds, we specially allocate shmem segments. The layout
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// is as follows
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//
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// Page 0: "front sentinel"
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// size of mapping
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// magic bytes
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// Page 1 through n-1:
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// user data
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// Page n: "back sentinel"
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// [nothing]
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//
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// The mapping can be in one of the following states, wrt to the
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// current process.
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//
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// State "unmapped": all pages are mapped with no access rights.
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//
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// State "mapping": all pages are mapped with read/write access.
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//
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// State "mapped": the front and back sentinels are mapped with no
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// access rights, and all the other pages are mapped with
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// read/write access.
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//
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// When a SharedMemory segment is first allocated, it starts out in
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// the "mapping" state for the process that allocates the segment, and
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// in the "unmapped" state for the other process. The allocating
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// process will then create a Shmem, which takes the segment into the
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// "mapped" state, where it can be accessed by clients.
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//
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// When a Shmem is sent to another process in an IPDL message, the
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// segment transitions into the "unmapped" state for the sending
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// process, and into the "mapping" state for the receiving process.
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// The receiving process will then create a Shmem from the underlying
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// segment, and take the segment into the "mapped" state.
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//
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// In the "mapping" state, we use the front sentinel to verify the
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// integrity of the shmem segment. If valid, it has a size_t
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// containing the number of bytes the user allocated followed by the
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// magic bytes above.
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//
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// In the "mapped" state, the front and back sentinels have no access
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// rights. They act as guards against buffer overflows and underflows
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// in client code; if clients touch a sentinel, they die with SIGSEGV.
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//
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// The "unmapped" state is used to enforce single-owner semantics of
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// the shmem segment. If a process other than the current owner tries
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// to touch the segment, it dies with SIGSEGV.
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//
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Shmem::Shmem(IHadBetterBeIPDLCodeCallingThis_OtherwiseIAmADoodyhead,
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SharedMemory* aSegment, id_t aId) :
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mSegment(aSegment),
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mData(nullptr),
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mSize(0)
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{
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MOZ_ASSERT(mSegment, "null segment");
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MOZ_ASSERT(aId != 0, "invalid ID");
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Unprotect(mSegment);
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Header* header;
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char* frontSentinel;
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char* data;
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char* backSentinel;
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GetSections(aSegment, &header, &frontSentinel, &data, &backSentinel);
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// do a quick validity check to avoid weird-looking crashes in libc
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char check = *frontSentinel;
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(void)check;
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MOZ_ASSERT(!strncmp(header->mMagic, sMagic, sizeof(sMagic)),
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"invalid segment");
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mSize = static_cast<size_t>(header->mSize);
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size_t pageSize = SharedMemory::SystemPageSize();
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// transition into the "mapped" state by protecting the front and
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// back sentinels (which guard against buffer under/overflows)
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mSegment->Protect(frontSentinel, pageSize, RightsNone);
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mSegment->Protect(backSentinel, pageSize, RightsNone);
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// don't set these until we know they're valid
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mData = data;
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mId = aId;
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}
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void
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Shmem::AssertInvariants() const
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{
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MOZ_ASSERT(mSegment, "null segment");
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MOZ_ASSERT(mData, "null data pointer");
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MOZ_ASSERT(mSize > 0, "invalid size");
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// if the segment isn't owned by the current process, these will
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// trigger SIGSEGV
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char checkMappingFront = *reinterpret_cast<char*>(mData);
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char checkMappingBack = *(reinterpret_cast<char*>(mData) + mSize - 1);
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// avoid "unused" warnings for these variables:
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Unused << checkMappingFront;
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Unused << checkMappingBack;
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}
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void
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Shmem::RevokeRights(IHadBetterBeIPDLCodeCallingThis_OtherwiseIAmADoodyhead)
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{
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AssertInvariants();
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size_t pageSize = SharedMemory::SystemPageSize();
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Header* header = GetHeader(mSegment);
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// Open this up for reading temporarily
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mSegment->Protect(reinterpret_cast<char*>(header), pageSize, RightsRead);
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if (!header->mUnsafe) {
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Protect(mSegment);
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} else {
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mSegment->Protect(reinterpret_cast<char*>(header), pageSize, RightsNone);
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}
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}
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// static
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already_AddRefed<Shmem::SharedMemory>
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Shmem::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)
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{
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NS_ASSERTION(aNBytes <= UINT32_MAX, "Will truncate shmem segment size!");
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MOZ_ASSERT(!aProtect || !aUnsafe, "protect => !unsafe");
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size_t pageSize = SharedMemory::SystemPageSize();
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// |2*pageSize| is for the front and back sentinel
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RefPtr<SharedMemory> segment = CreateSegment(aType, aNBytes, 2*pageSize);
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if (!segment) {
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return nullptr;
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}
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Header* header;
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char *frontSentinel;
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char *data;
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char *backSentinel;
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GetSections(segment, &header, &frontSentinel, &data, &backSentinel);
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// initialize the segment with Shmem-internal information
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// NB: this can't be a static assert because technically pageSize
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// isn't known at compile time, event though in practice it's always
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// going to be 4KiB
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MOZ_ASSERT(sizeof(Header) <= pageSize,
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"Shmem::Header has gotten too big");
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memcpy(header->mMagic, sMagic, sizeof(sMagic));
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header->mSize = static_cast<uint32_t>(aNBytes);
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header->mUnsafe = aUnsafe;
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if (aProtect)
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Protect(segment);
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return segment.forget();
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}
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// static
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already_AddRefed<Shmem::SharedMemory>
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Shmem::OpenExisting(IHadBetterBeIPDLCodeCallingThis_OtherwiseIAmADoodyhead,
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const IPC::Message& aDescriptor,
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id_t* aId,
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bool aProtect)
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{
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size_t size;
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size_t pageSize = SharedMemory::SystemPageSize();
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// |2*pageSize| is for the front and back sentinels
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RefPtr<SharedMemory> segment = ReadSegment(aDescriptor, aId, &size, 2*pageSize);
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if (!segment) {
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return nullptr;
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}
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Header* header = GetHeader(segment);
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if (size != header->mSize) {
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// Deallocation should zero out the header, so check for that.
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if (header->mSize || header->mUnsafe || header->mMagic[0] ||
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memcmp(header->mMagic, &header->mMagic[1], sizeof(header->mMagic)-1)) {
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NS_ERROR("Wrong size for this Shmem!");
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} else {
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NS_WARNING("Shmem was deallocated");
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}
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return nullptr;
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}
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// The caller of this function may not know whether the segment is
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// unsafe or not
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if (!header->mUnsafe && aProtect)
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Protect(segment);
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return segment.forget();
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}
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// static
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void
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Shmem::Dealloc(IHadBetterBeIPDLCodeCallingThis_OtherwiseIAmADoodyhead,
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SharedMemory* aSegment)
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{
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if (!aSegment)
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return;
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size_t pageSize = SharedMemory::SystemPageSize();
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Header* header;
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char *frontSentinel;
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char *data;
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char *backSentinel;
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GetSections(aSegment, &header, &frontSentinel, &data, &backSentinel);
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aSegment->Protect(frontSentinel, pageSize, RightsWrite | RightsRead);
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memset(header->mMagic, 0, sizeof(sMagic));
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header->mSize = 0;
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header->mUnsafe = false; // make it "safe" so as to catch errors
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DestroySegment(aSegment);
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}
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#else // !defined(DEBUG)
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// static
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already_AddRefed<Shmem::SharedMemory>
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Shmem::Alloc(IHadBetterBeIPDLCodeCallingThis_OtherwiseIAmADoodyhead,
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size_t aNBytes,
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SharedMemoryType aType,
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bool /*unused*/,
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bool /*unused*/)
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{
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RefPtr<SharedMemory> segment = CreateSegment(aType, aNBytes, sizeof(uint32_t));
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if (!segment) {
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return nullptr;
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}
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*PtrToSize(segment) = static_cast<uint32_t>(aNBytes);
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return segment.forget();
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}
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// static
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already_AddRefed<Shmem::SharedMemory>
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Shmem::OpenExisting(IHadBetterBeIPDLCodeCallingThis_OtherwiseIAmADoodyhead,
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const IPC::Message& aDescriptor,
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id_t* aId,
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bool /*unused*/)
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{
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size_t size;
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RefPtr<SharedMemory> segment = ReadSegment(aDescriptor, aId, &size, sizeof(uint32_t));
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if (!segment) {
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return nullptr;
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}
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// this is the only validity check done in non-DEBUG builds
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if (size != static_cast<size_t>(*PtrToSize(segment))) {
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return nullptr;
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}
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return segment.forget();
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}
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// static
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void
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Shmem::Dealloc(IHadBetterBeIPDLCodeCallingThis_OtherwiseIAmADoodyhead,
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SharedMemory* aSegment)
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{
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DestroySegment(aSegment);
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}
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#endif // if defined(DEBUG)
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IPC::Message*
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Shmem::ShareTo(IHadBetterBeIPDLCodeCallingThis_OtherwiseIAmADoodyhead,
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base::ProcessId aTargetPid,
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int32_t routingId)
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{
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AssertInvariants();
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IPC::Message *msg = new ShmemCreated(routingId, mId, mSize, mSegment->Type());
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if (!mSegment->ShareHandle(aTargetPid, msg)) {
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return nullptr;
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}
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// close the handle to the segment after it is shared
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mSegment->CloseHandle();
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return msg;
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}
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IPC::Message*
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Shmem::UnshareFrom(IHadBetterBeIPDLCodeCallingThis_OtherwiseIAmADoodyhead,
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base::ProcessId aTargetPid,
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int32_t routingId)
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{
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AssertInvariants();
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return new ShmemDestroyed(routingId, mId);
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}
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} // namespace ipc
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} // namespace mozilla
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