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/*
* Copyright 2012 Google Inc.
*
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*/
#ifndef SkThreadPool_DEFINED
#define SkThreadPool_DEFINED
#include "SkCondVar.h"
#include "SkRunnable.h"
#include "SkTDArray.h"
#include "SkTInternalLList.h"
#include "SkThreadUtils.h"
#include "SkTypes.h"
#if defined(SK_BUILD_FOR_UNIX) || defined(SK_BUILD_FOR_MAC) || defined(SK_BUILD_FOR_ANDROID)
# include <unistd.h>
#endif
// Returns the number of cores on this machine.
static inline int num_cores() {
#if defined(SK_BUILD_FOR_WIN32)
SYSTEM_INFO sysinfo;
GetSystemInfo(&sysinfo);
return sysinfo.dwNumberOfProcessors;
#elif defined(SK_BUILD_FOR_UNIX) || defined(SK_BUILD_FOR_MAC) || defined(SK_BUILD_FOR_ANDROID)
return (int) sysconf(_SC_NPROCESSORS_ONLN);
#else
return 1;
#endif
}
template <typename T>
class SkTThreadPool {
public:
/**
* Create a threadpool with count threads, or one thread per core if kThreadPerCore.
*/
static const int kThreadPerCore = -1;
explicit SkTThreadPool(int count);
~SkTThreadPool();
/**
* Queues up an SkRunnable to run when a thread is available, or synchronously if count is 0.
* Does not take ownership. NULL is a safe no-op. If T is not void, the runnable will be passed
* a reference to a T on the thread's local stack.
*/
void add(SkTRunnable<T>*);
/**
* Same as add, but adds the runnable as the very next to run rather than enqueueing it.
*/
void addNext(SkTRunnable<T>*);
/**
* Block until all added SkRunnables have completed. Once called, calling add() is undefined.
*/
void wait();
private:
struct LinkedRunnable {
SkTRunnable<T>* fRunnable; // Unowned.
SK_DECLARE_INTERNAL_LLIST_INTERFACE(LinkedRunnable);
};
enum State {
kRunning_State, // Normal case. We've been constructed and no one has called wait().
kWaiting_State, // wait has been called, but there still might be work to do or being done.
kHalting_State, // There's no work to do and no thread is busy. All threads can shut down.
};
void addSomewhere(SkTRunnable<T>* r,
void (SkTInternalLList<LinkedRunnable>::*)(LinkedRunnable*));
SkTInternalLList<LinkedRunnable> fQueue;
SkCondVar fReady;
SkTDArray<SkThread*> fThreads;
State fState;
int fBusyThreads;
static void Loop(void*); // Static because we pass in this.
};
template <typename T>
SkTThreadPool<T>::SkTThreadPool(int count) : fState(kRunning_State), fBusyThreads(0) {
if (count < 0) {
count = num_cores();
}
// Create count threads, all running SkTThreadPool::Loop.
for (int i = 0; i < count; i++) {
SkThread* thread = SkNEW_ARGS(SkThread, (&SkTThreadPool::Loop, this));
*fThreads.append() = thread;
thread->start();
}
}
template <typename T>
SkTThreadPool<T>::~SkTThreadPool() {
if (kRunning_State == fState) {
this->wait();
}
}
namespace SkThreadPoolPrivate {
template <typename T>
struct ThreadLocal {
void run(SkTRunnable<T>* r) { r->run(data); }
T data;
};
template <>
struct ThreadLocal<void> {
void run(SkTRunnable<void>* r) { r->run(); }
};
} // namespace SkThreadPoolPrivate
template <typename T>
void SkTThreadPool<T>::addSomewhere(SkTRunnable<T>* r,
void (SkTInternalLList<LinkedRunnable>::* f)(LinkedRunnable*)) {
if (r == NULL) {
return;
}
if (fThreads.isEmpty()) {
SkThreadPoolPrivate::ThreadLocal<T> threadLocal;
threadLocal.run(r);
return;
}
LinkedRunnable* linkedRunnable = SkNEW(LinkedRunnable);
linkedRunnable->fRunnable = r;
fReady.lock();
SkASSERT(fState != kHalting_State); // Shouldn't be able to add work when we're halting.
(fQueue.*f)(linkedRunnable);
fReady.signal();
fReady.unlock();
}
template <typename T>
void SkTThreadPool<T>::add(SkTRunnable<T>* r) {
this->addSomewhere(r, &SkTInternalLList<LinkedRunnable>::addToTail);
}
template <typename T>
void SkTThreadPool<T>::addNext(SkTRunnable<T>* r) {
this->addSomewhere(r, &SkTInternalLList<LinkedRunnable>::addToHead);
}
template <typename T>
void SkTThreadPool<T>::wait() {
fReady.lock();
fState = kWaiting_State;
fReady.broadcast();
fReady.unlock();
// Wait for all threads to stop.
for (int i = 0; i < fThreads.count(); i++) {
fThreads[i]->join();
SkDELETE(fThreads[i]);
}
SkASSERT(fQueue.isEmpty());
}
template <typename T>
/*static*/ void SkTThreadPool<T>::Loop(void* arg) {
// The SkTThreadPool passes itself as arg to each thread as they're created.
SkTThreadPool<T>* pool = static_cast<SkTThreadPool<T>*>(arg);
SkThreadPoolPrivate::ThreadLocal<T> threadLocal;
while (true) {
// We have to be holding the lock to read the queue and to call wait.
pool->fReady.lock();
while(pool->fQueue.isEmpty()) {
// Does the client want to stop and are all the threads ready to stop?
// If so, we move into the halting state, and whack all the threads so they notice.
if (kWaiting_State == pool->fState && pool->fBusyThreads == 0) {
pool->fState = kHalting_State;
pool->fReady.broadcast();
}
// Any time we find ourselves in the halting state, it's quitting time.
if (kHalting_State == pool->fState) {
pool->fReady.unlock();
return;
}
// wait yields the lock while waiting, but will have it again when awoken.
pool->fReady.wait();
}
// We've got the lock back here, no matter if we ran wait or not.
// The queue is not empty, so we have something to run. Claim it.
LinkedRunnable* r = pool->fQueue.head();
pool->fQueue.remove(r);
// Having claimed our SkRunnable, we now give up the lock while we run it.
// Otherwise, we'd only ever do work on one thread at a time, which rather
// defeats the point of this code.
pool->fBusyThreads++;
pool->fReady.unlock();
// OK, now really do the work.
threadLocal.run(r->fRunnable);
SkDELETE(r);
// Let everyone know we're not busy.
pool->fReady.lock();
pool->fBusyThreads--;
pool->fReady.unlock();
}
SkASSERT(false); // Unreachable. The only exit happens when pool->fState is kHalting_State.
}
typedef SkTThreadPool<void> SkThreadPool;
#endif
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