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/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
* vim: set ts=8 sts=2 et sw=2 tw=80:
* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
#ifndef builtin_AtomicsObject_h
#define builtin_AtomicsObject_h
#include "mozilla/Maybe.h"
#include "mozilla/TimeStamp.h"
#include "threading/ConditionVariable.h"
#include "threading/ProtectedData.h" // js::ThreadData
#include "vm/NativeObject.h"
#include "vm/PlainObject.h"
namespace js {
class SharedArrayRawBuffer;
class AtomicsObject : public NativeObject {
public:
static const JSClass class_;
};
enum class FutexWaiterKind { Sync, Async, ListHead };
class FutexWaiter;
class SyncFutexWaiter;
class AsyncFutexWaiter;
class FutexWaiterListNode {
private:
FutexWaiterListNode* next_ = nullptr; // Lower priority node in waiter list
FutexWaiterListNode* prev_ = nullptr; // Higher priority node in waiter list
protected:
explicit FutexWaiterListNode(FutexWaiterKind kind) : kind_(kind) {}
FutexWaiterKind kind_;
public:
FutexWaiter* toWaiter() {
MOZ_ASSERT(kind_ != FutexWaiterKind::ListHead);
return reinterpret_cast<FutexWaiter*>(this);
}
FutexWaiterKind kind() const { return kind_; }
FutexWaiterListNode* next() { return next_; }
void setNext(FutexWaiterListNode* next) { next_ = next; }
FutexWaiterListNode* prev() { return prev_; }
void setPrev(FutexWaiterListNode* prev) { prev_ = prev; }
};
class FutexWaiterListHead : public FutexWaiterListNode {
public:
FutexWaiterListHead() : FutexWaiterListNode(FutexWaiterKind::ListHead) {
setNext(this);
setPrev(this);
}
~FutexWaiterListHead();
};
class FutexThread {
friend class AutoLockFutexAPI;
public:
[[nodiscard]] static bool initialize();
static void destroy();
static void lock();
static void unlock();
FutexThread();
[[nodiscard]] bool initInstance();
void destroyInstance();
// Parameters to notify().
enum NotifyReason {
NotifyExplicit, // Being asked to wake up by another thread
NotifyForJSInterrupt // Interrupt requested
};
// Result codes from wait() and atomics_wait_impl().
enum class WaitResult {
Error, // Error has been reported, just propagate error signal
NotEqual, // Did not wait because the values differed
OK, // Waited and was woken
TimedOut // Waited and timed out
};
// Block the calling thread and wait.
//
// The futex lock must be held around this call.
//
// The timeout is the number of milliseconds, with fractional
// times allowed; specify mozilla::Nothing() for an indefinite
// wait.
//
// wait() will not wake up spuriously.
[[nodiscard]] WaitResult wait(
JSContext* cx, js::UniqueLock<js::Mutex>& locked,
const mozilla::Maybe<mozilla::TimeDuration>& timeout);
// Notify the thread this is associated with.
//
// The futex lock must be held around this call. (The sleeping
// thread will not wake up until the caller of Atomics.notify()
// releases the lock.)
//
// If the thread is not waiting then this method does nothing.
//
// If the thread is waiting in a call to wait() and the
// reason is NotifyExplicit then the wait() call will return
// with Woken.
//
// If the thread is waiting in a call to wait() and the
// reason is NotifyForJSInterrupt then the wait() will return
// with WaitingNotifiedForInterrupt; in the latter case the caller
// of wait() must handle the interrupt.
void notify(NotifyReason reason);
bool isWaiting();
// If canWait() returns false (the default) then wait() is disabled
// on the thread to which the FutexThread belongs.
bool canWait() { return canWait_; }
void setCanWait(bool flag) { canWait_ = flag; }
private:
enum FutexState {
Idle, // We are not waiting or woken
Waiting, // We are waiting, nothing has happened yet
WaitingNotifiedForInterrupt, // We are waiting, but have been interrupted,
// and have not yet started running the
// interrupt handler
WaitingInterrupted, // We are waiting, but have been interrupted
// and are running the interrupt handler
Woken // Woken by a script call to Atomics.notify
};
// Condition variable that this runtime will wait on.
js::ConditionVariable* cond_;
// Current futex state for this runtime. When not in a wait this
// is Idle; when in a wait it is Waiting or the reason the futex
// is about to wake up.
FutexState state_;
// Shared futex lock for all runtimes. We can perhaps do better,
// but any lock will need to be per-domain (consider SharedWorker)
// or coarser.
static mozilla::Atomic<js::Mutex*, mozilla::SequentiallyConsistent> lock_;
// A flag that controls whether waiting is allowed.
ThreadData<bool> canWait_;
};
// Go to sleep if the int32_t value at the given address equals `value`.
[[nodiscard]] FutexThread::WaitResult atomics_wait_impl(
JSContext* cx, SharedArrayRawBuffer* sarb, size_t byteOffset, int32_t value,
const mozilla::Maybe<mozilla::TimeDuration>& timeout);
// Go to sleep if the int64_t value at the given address equals `value`.
[[nodiscard]] FutexThread::WaitResult atomics_wait_impl(
JSContext* cx, SharedArrayRawBuffer* sarb, size_t byteOffset, int64_t value,
const mozilla::Maybe<mozilla::TimeDuration>& timeout);
// If the int32_t value at the given address equals `value`, return a result
// object containing a promise that will be resolved when that address is
// notified.
[[nodiscard]] PlainObject* atomics_wait_async_impl(
JSContext* cx, SharedArrayRawBuffer* sarb, size_t byteOffset, int32_t value,
const mozilla::Maybe<mozilla::TimeDuration>& timeout);
// If the int64_t value at the given address equals `value`, return a result
// object containing a promise that will be resolved when that address is
// notified.
[[nodiscard]] PlainObject* atomics_wait_async_impl(
JSContext* cx, SharedArrayRawBuffer* sarb, size_t byteOffset, int64_t value,
const mozilla::Maybe<mozilla::TimeDuration>& timeout);
// Notify some waiters on the given address. If `count` is negative then notify
// all. The return value is nonnegative and is the number of waiters woken. If
// the number of waiters woken exceeds INT64_MAX then this never returns. If
// `count` is nonnegative then the woken out parameter is never greater than
// `count`.
[[nodiscard]] bool atomics_notify_impl(JSContext* cx,
SharedArrayRawBuffer* sarb,
size_t byteOffset, int64_t count,
int64_t* woken);
} /* namespace js */
#endif /* builtin_AtomicsObject_h */