src/third_party/mozjs/js/src/vm/ThreadPool.h

/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
 * vim: set ts=8 sts=4 et sw=4 tw=99:
 * 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
 * file, You can obtain one at http://mozilla.org/MPL/2.0/. */

#ifndef vm_ThreadPool_h
#define vm_ThreadPool_h

#include <stddef.h>
#include "mozilla/StandardInteger.h"
#include "js/Vector.h"
#include "jsalloc.h"

#ifdef JS_THREADSAFE
#if defined(STARBOARD)
#include "starboard/client_porting/pr_starboard/pr_starboard.h"
#else  // defined(STARBOARD)
#  include "prtypes.h"
#  include "prlock.h"
#  include "prcvar.h"
#endif  // defined(STARBOARD)
#endif

struct JSContext;
struct JSRuntime;
struct JSCompartment;
class JSScript;

namespace js {

class ThreadPoolWorker;

typedef void (*TaskFun)(void *userdata, uint32_t workerId, uintptr_t stackLimit);

class TaskExecutor
{
  public:
    virtual void executeFromWorker(uint32_t workerId, uintptr_t stackLimit) = 0;
};

// ThreadPool used for parallel JavaScript execution as well as
// parallel compilation.  Unless you are building a new kind of
// parallel service, it is very likely that you do not wish to
// interact with the threadpool directly.  In particular, if you wish
// to execute JavaScript in parallel, you probably want to look at
// |js::ForkJoin| in |forkjoin.cpp|.
//
// The ThreadPool always maintains a fixed pool of worker threads.
// You can query the number of worker threads via the method
// |numWorkers()|.  Note that this number may be zero (generally if
// threads are disabled, or when manually specified for benchmarking
// purposes).
//
// You can either submit jobs in one of two ways.  The first is
// |submitOne()|, which submits a job to be executed by one worker
// thread (this will fail if there are no worker threads).  The job
// will be enqueued and executed by some worker (the current scheduler
// uses round-robin load balancing; something more sophisticated,
// e.g. a central queue or work stealing, might be better).
//
// The second way to submit a job is using |submitAll()|---in this
// case, the job will be executed by all worker threads.  This does
// not fail if there are no worker threads, it simply does nothing.
// Of course, each thread may have any number of previously submitted
// things that they are already working on, and so they will finish
// those before they get to this job.  Therefore it is possible to
// have some worker threads pick up (and even finish) their piece of
// the job before others have even started.
class ThreadPool
{
  private:
    friend class ThreadPoolWorker;

    // Initialized at startup only:
    JSRuntime *const runtime_;
    js::Vector<ThreadPoolWorker*, 8, SystemAllocPolicy> workers_;

    // Number of workers we will start, when we actually start them
    size_t numWorkers_;

    // Next worker for |submitOne()|. Atomically modified.
    uint32_t nextId_;

    bool lazyStartWorkers(JSContext *cx);
    void terminateWorkers();
    void terminateWorkersAndReportOOM(JSContext *cx);

  public:
    ThreadPool(JSRuntime *rt);
    ~ThreadPool();

    bool init();

    // Return number of worker threads in the pool.
    size_t numWorkers() { return numWorkers_; }

    // See comment on class:
    bool submitOne(JSContext *cx, TaskExecutor *executor);
    bool submitAll(JSContext *cx, TaskExecutor *executor);

    // Wait until all worker threads have finished their current set
    // of jobs and then return.  You must not submit new jobs after
    // invoking |terminate()|.
    bool terminate();
};

} // namespace js

#endif /* vm_ThreadPool_h */