mirror of
https://github.com/classilla/tenfourfox.git
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176 lines
5.6 KiB
C++
176 lines
5.6 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 vm_SharedArrayObject_h
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#define vm_SharedArrayObject_h
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#include "mozilla/Atomics.h"
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#include "jsapi.h"
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#include "jsobj.h"
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#include "jstypes.h"
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#include "gc/Barrier.h"
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#include "vm/ArrayBufferObject.h"
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typedef struct JSProperty JSProperty;
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namespace js {
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class FutexWaiter;
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/*
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* SharedArrayRawBuffer
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*
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* A bookkeeping object always stored immediately before the raw buffer.
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* The buffer itself is mmap()'d and refcounted.
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* SharedArrayBufferObjects and AsmJS code may hold references.
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*
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* |<------ sizeof ------>|<- length ->|
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*
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* | waste | SharedArrayRawBuffer | data array | waste |
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*
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* Observe that if we want to map the data array on a specific address, such
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* as absolute zero (bug 1056027), then the SharedArrayRawBuffer cannot be
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* prefixed to the data array, it has to be a separate object, also in
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* shared memory. (That would get rid of ~4KB of waste, as well.) Very little
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* else would have to change throughout the engine, the SARB would point to
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* the data array using a constant pointer, instead of computing its
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* address.
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*/
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class SharedArrayRawBuffer
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{
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private:
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mozilla::Atomic<uint32_t, mozilla::ReleaseAcquire> refcount;
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uint32_t length;
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// A list of structures representing tasks waiting on some
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// location within this buffer.
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FutexWaiter* waiters_;
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protected:
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SharedArrayRawBuffer(uint8_t* buffer, uint32_t length)
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: refcount(1),
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length(length),
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waiters_(nullptr)
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{
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MOZ_ASSERT(buffer == dataPointerShared());
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}
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public:
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static SharedArrayRawBuffer* New(JSContext* cx, uint32_t length);
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// This may be called from multiple threads. The caller must take
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// care of mutual exclusion.
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FutexWaiter* waiters() const {
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return waiters_;
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}
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// This may be called from multiple threads. The caller must take
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// care of mutual exclusion.
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void setWaiters(FutexWaiter* waiters) {
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waiters_ = waiters;
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}
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SharedMem<uint8_t*> dataPointerShared() const {
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uint8_t* ptr = reinterpret_cast<uint8_t*>(const_cast<SharedArrayRawBuffer*>(this));
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return SharedMem<uint8_t*>::shared(ptr + sizeof(SharedArrayRawBuffer));
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}
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uint32_t byteLength() const {
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return length;
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}
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void addReference();
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void dropReference();
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};
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/*
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* SharedArrayBufferObject
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*
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* When transferred to a WebWorker, the buffer is not neutered on the
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* parent side, and both child and parent reference the same buffer.
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*
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* The underlying memory is memory-mapped and reference counted
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* (across workers and/or processes). The SharedArrayBuffer object
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* has a finalizer that decrements the refcount, the last one to leave
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* (globally) unmaps the memory. The sender ups the refcount before
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* transmitting the memory to another worker.
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*
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* SharedArrayBufferObject (or really the underlying memory) /is
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* racy/: more than one worker can access the memory at the same time.
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*
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* A TypedArrayObject (a view) references a SharedArrayBuffer
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* and keeps it alive. The SharedArrayBuffer does /not/ reference its
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* views.
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*/
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class SharedArrayBufferObject : public ArrayBufferObjectMaybeShared
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{
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static bool byteLengthGetterImpl(JSContext* cx, const CallArgs& args);
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public:
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// RAWBUF_SLOT holds a pointer (as "private" data) to the
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// SharedArrayRawBuffer object, which is manually managed storage.
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static const uint8_t RAWBUF_SLOT = 0;
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static const uint8_t RESERVED_SLOTS = 1;
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static const Class class_;
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static const Class protoClass;
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static const JSFunctionSpec jsfuncs[];
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static const JSFunctionSpec jsstaticfuncs[];
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static bool byteLengthGetter(JSContext* cx, unsigned argc, Value* vp);
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static bool fun_isView(JSContext* cx, unsigned argc, Value* vp);
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static bool class_constructor(JSContext* cx, unsigned argc, Value* vp);
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// Create a SharedArrayBufferObject with a new SharedArrayRawBuffer.
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static SharedArrayBufferObject* New(JSContext* cx, uint32_t length);
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// Create a SharedArrayBufferObject using an existing SharedArrayRawBuffer.
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static SharedArrayBufferObject* New(JSContext* cx, SharedArrayRawBuffer* buffer);
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static void Finalize(FreeOp* fop, JSObject* obj);
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static void addSizeOfExcludingThis(JSObject* obj, mozilla::MallocSizeOf mallocSizeOf,
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JS::ClassInfo* info);
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SharedArrayRawBuffer* rawBufferObject() const;
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// Invariant: This method does not cause GC and can be called
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// without anchoring the object it is called on.
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uintptr_t globalID() const {
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// The buffer address is good enough as an ID provided the memory is not shared
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// between processes or, if it is, it is mapped to the same address in every
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// process. (At the moment, shared memory cannot be shared between processes.)
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return dataPointerShared().asValue();
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}
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uint32_t byteLength() const {
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return rawBufferObject()->byteLength();
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}
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SharedMem<uint8_t*> dataPointerShared() const {
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return rawBufferObject()->dataPointerShared();
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}
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private:
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void acceptRawBuffer(SharedArrayRawBuffer* buffer);
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void dropRawBuffer();
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};
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bool IsSharedArrayBuffer(HandleValue v);
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bool IsSharedArrayBuffer(HandleObject o);
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bool IsSharedArrayBuffer(JSObject* o);
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SharedArrayBufferObject& AsSharedArrayBuffer(HandleObject o);
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} // namespace js
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#endif // vm_SharedArrayObject_h
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