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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 threading_Thread_h
#define threading_Thread_h
#include "mozilla/Atomics.h"
#include "mozilla/TimeStamp.h"
#include <stdint.h>
#include <type_traits>
#include <utility>
#include "js/Initialization.h"
#include "js/Utility.h"
#include "threading/LockGuard.h"
#include "threading/Mutex.h"
#include "threading/ThreadId.h"
#include "vm/MutexIDs.h"
#ifdef XP_WIN
# define THREAD_RETURN_TYPE unsigned int
# define THREAD_CALL_API __stdcall
#else
# define THREAD_RETURN_TYPE void*
# define THREAD_CALL_API
#endif
namespace js {
namespace detail {
template <typename F, typename... Args>
class ThreadTrampoline;
} // namespace detail
// Execute the given functor concurrent with the currently executing instruction
// stream and within the current address space. Use with care.
class Thread {
public:
// Provides optional parameters to a Thread.
class Options {
size_t stackSize_;
public:
Options() : stackSize_(0) {}
Options& setStackSize(size_t sz) {
stackSize_ = sz;
return *this;
}
size_t stackSize() const { return stackSize_; }
};
// Create a Thread in an initially unjoinable state. A thread of execution can
// be created for this Thread by calling |init|. Some of the thread's
// properties may be controlled by passing options to this constructor.
template <typename O = Options,
// SFINAE to make sure we don't try and treat functors for the other
// constructor as an Options and vice versa.
typename NonConstO = std::remove_const_t<O>,
typename DerefO = std::remove_reference_t<NonConstO>,
typename = std::enable_if_t<std::is_same_v<DerefO, Options>>>
explicit Thread(O&& options = Options())
: options_(std::forward<O>(options)) {
MOZ_ASSERT(isInitialized());
}
// Start a thread of execution at functor |f| with parameters |args|. This
// method will return false if thread creation fails. This Thread must not
// already have been created. Note that the arguments must be either POD or
// rvalue references (std::move). Attempting to pass a reference will
// result in the value being copied, which may not be the intended behavior.
// See the comment below on ThreadTrampoline::args for an explanation.
template <typename F, typename... Args>
[[nodiscard]] bool init(F&& f, Args&&... args) {
MOZ_RELEASE_ASSERT(id_ == ThreadId());
using Trampoline = detail::ThreadTrampoline<F, Args...>;
auto trampoline =
js_new<Trampoline>(std::forward<F>(f), std::forward<Args>(args)...);
if (!trampoline) {
return false;
}
bool result;
{
// We hold this lock while create() sets the thread id.
LockGuard<Mutex> lock(trampoline->createMutex);
result = create(Trampoline::Start, trampoline);
}
if (!result) {
// Trampoline should be deleted outside of the above lock.
js_delete(trampoline);
return false;
}
return true;
}
// The thread must be joined or detached before destruction.
~Thread();
// Move the thread into the detached state without blocking. In the detached
// state, the thread continues to run until it exits, but cannot be joined.
// After this method returns, this Thread no longer represents a thread of
// execution. When the thread exits, its resources will be cleaned up by the
// system. At process exit, if the thread is still running, the thread's TLS
// storage will be destructed, but the thread stack will *not* be unrolled.
void detach();
// Block the current thread until this Thread returns from the functor it was
// created with. The thread's resources will be cleaned up before this
// function returns. After this method returns, this Thread no longer
// represents a thread of execution.
void join();
// Return true if this thread has not yet been joined or detached. If this
// method returns false, this Thread does not have an associated thread of
// execution, for example, if it has been previously moved or joined.
bool joinable();
// Returns the id of this thread if this represents a thread of execution or
// the default constructed Id() if not. The thread ID is guaranteed to
// uniquely identify a thread and can be compared with the == operator.
ThreadId get_id();
// Allow threads to be moved so that they can be stored in containers.
Thread(Thread&& aOther);
Thread& operator=(Thread&& aOther);
private:
// Disallow copy as that's not sensible for unique resources.
Thread(const Thread&) = delete;
void operator=(const Thread&) = delete;
// Provide a process global ID to each thread.
ThreadId id_;
// Overridable thread creation options.
Options options_;
// Dispatch to per-platform implementation of thread creation.
[[nodiscard]] bool create(THREAD_RETURN_TYPE(THREAD_CALL_API* aMain)(void*),
void* aArg);
// An internal version of JS_IsInitialized() that returns whether SpiderMonkey
// is currently initialized or is in the process of being initialized.
static inline bool isInitialized() {
using namespace JS::detail;
return libraryInitState == InitState::Initializing ||
libraryInitState == InitState::Running;
}
};
namespace ThisThread {
// Set the current thread name. Note that setting the thread name may not be
// available on all platforms; on these platforms setName() will simply do
// nothing.
void SetName(const char* name);
// Get the current thread name. As with SetName, not available on all
// platforms. On these platforms getName() will give back an empty string (by
// storing NUL in nameBuffer[0]). 'len' is the bytes available to be written in
// 'nameBuffer', including the terminating NUL.
void GetName(char* nameBuffer, size_t len);
// Causes the current thread to sleep until the
// number of real-time milliseconds specified have elapsed.
void SleepMilliseconds(size_t ms);
} // namespace ThisThread
namespace detail {
// Platform thread APIs allow passing a single void* argument to the target
// thread. This class is responsible for safely ferrying the arg pack and
// functor across that void* membrane and running it in the other thread.
template <typename F, typename... Args>
class ThreadTrampoline {
// The functor to call.
F f;
// A std::decay copy of the arguments, as specified by std::thread. Using an
// rvalue reference for the arguments to Thread and ThreadTrampoline gives us
// move semantics for large structures, allowing us to quickly and easily pass
// enormous amounts of data to a new thread. Unfortunately, there is a
// downside: rvalue references becomes lvalue references when used with POD
// types. This becomes dangerous when attempting to pass POD stored on the
// stack to the new thread; the rvalue reference will implicitly become an
// lvalue reference to the stack location. Thus, the value may not exist if
// the parent thread leaves the frame before the read happens in the new
// thread. To avoid this dangerous and highly non-obvious footgun, the
// standard requires a "decay" copy of the arguments at the cost of making it
// impossible to pass references between threads.
std::tuple<std::decay_t<Args>...> args;
// Protect the thread id during creation.
Mutex createMutex MOZ_UNANNOTATED;
// Thread can access createMutex.
friend class js::Thread;
public:
// Note that this template instatiation duplicates and is identical to the
// class template instantiation. It is required for perfect forwarding of
// rvalue references, which is only enabled for calls to a function template,
// even if the class template arguments are correct.
template <typename G, typename... ArgsT>
explicit ThreadTrampoline(G&& aG, ArgsT&&... aArgsT)
: f(std::forward<F>(aG)),
args(std::forward<Args>(aArgsT)...),
createMutex(mutexid::ThreadId) {}
static THREAD_RETURN_TYPE THREAD_CALL_API Start(void* aPack) {
auto* pack = static_cast<ThreadTrampoline<F, Args...>*>(aPack);
pack->callMain(std::index_sequence_for<Args...>{});
js_delete(pack);
return 0;
}
template <size_t... Indices>
void callMain(std::index_sequence<Indices...>) {
// Pretend createMutex is a semaphore and wait for a notification that the
// thread that spawned us is ready.
createMutex.lock();
createMutex.unlock();
f(std::move(std::get<Indices>(args))...);
}
};
} // namespace detail
} // namespace js
#undef THREAD_RETURN_TYPE
#endif // threading_Thread_h