Revert of SkThreadPool ~~> SkTaskGroup

src/utils/SkThreadPool.h

+/*
+ * 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