Modernize atomics in SkTaskGroup's threadpool.

src/core/SkTaskGroup.cpp

+/*
+ * Copyright 2014 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
 #include "SkTaskGroup.h"
 
 #include "SkCondVar.h"
 #include "SkRunnable.h"
 #include "SkTDArray.h"
 #include "SkThread.h"
 #include "SkThreadUtils.h"
 
 #if defined(SK_BUILD_FOR_WIN32)
     static inline int num_cores() {
         SYSTEM_INFO sysinfo;
         GetSystemInfo(&sysinfo);
         return sysinfo.dwNumberOfProcessors;
     }
 #else
     #include <unistd.h>
     static inline int num_cores() {
         return (int) sysconf(_SC_NPROCESSORS_ONLN);
     }
 #endif
 
 namespace {
 
 class ThreadPool : SkNoncopyable {
 public:
-    static void Add(SkRunnable* task, int32_t* pending) {
+    static void Add(SkRunnable* task, SkAtomic<int32_t>* pending) {
         if (!gGlobal) {  // If we have no threads, run synchronously.
             return task->run();
         }
         gGlobal->add(&CallRunnable, task, pending);
     }
 
-    static void Add(void (*fn)(void*), void* arg, int32_t* pending) {
+    static void Add(void (*fn)(void*), void* arg, SkAtomic<int32_t>* pending) {
         if (!gGlobal) {
             return fn(arg);
         }
         gGlobal->add(fn, arg, pending);
     }
 
-    static void Batch(void (*fn)(void*), void* args, int N, size_t stride, int32_t* pending) {
+    static void Batch(void (*fn)(void*), void* args, int N, size_t stride,
+                      SkAtomic<int32_t>* pending) {
         if (!gGlobal) {
             for (int i = 0; i < N; i++) { fn((char*)args + i*stride); }
             return;
         }
         gGlobal->batch(fn, args, N, stride, pending);
     }
 
-    static void Wait(int32_t* pending) {
+    static void Wait(SkAtomic<int32_t>* pending) {
         if (!gGlobal) {  // If we have no threads, the work must already be done.
-            SkASSERT(*pending == 0);
+            SkASSERT(pending->load(sk_memory_order_relaxed) == 0);
             return;
         }
-        while (sk_acquire_load(pending) > 0) {  // Pairs with sk_atomic_dec here or in Loop.
+        // Acquire pairs with decrement release here or in Loop.
+        while (pending->load(sk_memory_order_acquire) > 0) {
             // Lend a hand until our SkTaskGroup of interest is done.
             Work work;
             {
                 AutoLock lock(&gGlobal->fReady);
                 if (gGlobal->fWork.isEmpty()) {
                     // Someone has picked up all the work (including ours).  How nice of them!
                     // (They may still be working on it, so we can't assert *pending == 0 here.)
                     continue;
                 }
                 gGlobal->fWork.pop(&work);
             }
             // This Work isn't necessarily part of our SkTaskGroup of interest, but that's fine.
             // We threads gotta stick together.  We're always making forward progress.
             work.fn(work.arg);
-            sk_atomic_dec(work.pending);  // Release pairs with the sk_acquire_load() just above.
+            work.pending->fetch_add(-1, sk_memory_order_release);  // Pairs with load above.
         }
     }
 
 private:
     struct AutoLock {
         AutoLock(SkCondVar* c) : fC(c) { fC->lock(); }
         ~AutoLock() { fC->unlock(); }
     private:
         SkCondVar* fC;
     };
 
     static void CallRunnable(void* arg) { static_cast<SkRunnable*>(arg)->run(); }
 
     struct Work {
-        void (*fn)(void*);  // A function to call,
-        void* arg;          // its argument,
-        int32_t* pending;   // then sk_atomic_dec(pending) afterwards.
+        void (*fn)(void*);            // A function to call,
+        void* arg;                    // its argument,
+        SkAtomic<int32_t>* pending;   // then decrement pending afterwards.
     };
 
     explicit ThreadPool(int threads) : fDraining(false) {
         if (threads == -1) {
             threads = num_cores();
         }
         for (int i = 0; i < threads; i++) {
             fThreads.push(SkNEW_ARGS(SkThread, (&ThreadPool::Loop, this)));
             fThreads.top()->start();
         }
     }
 
     ~ThreadPool() {
         SkASSERT(fWork.isEmpty());  // All SkTaskGroups should be destroyed by now.
         {
             AutoLock lock(&fReady);
             fDraining = true;
             fReady.broadcast();
         }
         for (int i = 0; i < fThreads.count(); i++) {
             fThreads[i]->join();
         }
         SkASSERT(fWork.isEmpty());  // Can't hurt to double check.
         fThreads.deleteAll();
     }
 
-    void add(void (*fn)(void*), void* arg, int32_t* pending) {
+    void add(void (*fn)(void*), void* arg, SkAtomic<int32_t>* pending) {
         Work work = { fn, arg, pending };
-        sk_atomic_inc(pending);  // No barrier needed.
+        pending->fetch_add(+1, sk_memory_order_relaxed);  // No barrier needed.
         {
             AutoLock lock(&fReady);
             fWork.push(work);
             fReady.signal();
         }
     }
 
-    void batch(void (*fn)(void*), void* arg, int N, size_t stride, int32_t* pending) {
-        sk_atomic_add(pending, N);  // No barrier needed.
+    void batch(void (*fn)(void*), void* arg, int N, size_t stride, SkAtomic<int32_t>* pending) {
+        pending->fetch_add(+N, sk_memory_order_relaxed);  // No barrier needed.
         {
             AutoLock lock(&fReady);
             Work* batch = fWork.append(N);
             for (int i = 0; i < N; i++) {
                 Work work = { fn, (char*)arg + i*stride, pending };
                 batch[i] = work;
             }
             fReady.broadcast();
         }
     }
 
     static void Loop(void* arg) {
         ThreadPool* pool = (ThreadPool*)arg;
         Work work;
         while (true) {
             {
                 AutoLock lock(&pool->fReady);
                 while (pool->fWork.isEmpty()) {
                     if (pool->fDraining) {
                         return;
                     }
                     pool->fReady.wait();
                 }
                 pool->fWork.pop(&work);
             }
             work.fn(work.arg);
-            sk_atomic_dec(work.pending);  // Release pairs with sk_acquire_load() in Wait().
+            work.pending->fetch_add(-1, sk_memory_order_release);  // Pairs with load in Wait().
         }
     }
 
     SkTDArray<Work>      fWork;
     SkTDArray<SkThread*> fThreads;
     SkCondVar            fReady;
     bool                 fDraining;
 
     static ThreadPool* gGlobal;
     friend struct SkTaskGroup::Enabler;
@@ skipping 15 matching lines @@
 
 SkTaskGroup::SkTaskGroup() : fPending(0) {}
 
 void SkTaskGroup::wait()                            { ThreadPool::Wait(&fPending); }
 void SkTaskGroup::add(SkRunnable* task)             { ThreadPool::Add(task, &fPending); }
 void SkTaskGroup::add(void (*fn)(void*), void* arg) { ThreadPool::Add(fn, arg, &fPending); }
 void SkTaskGroup::batch (void (*fn)(void*), void* args, int N, size_t stride) {
     ThreadPool::Batch(fn, args, N, stride, &fPending);
 }