Change SkTaskGroup to use std::function.

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 "SkOnce.h"
 #include "SkRunnable.h"
 #include "SkSemaphore.h"
 #include "SkSpinlock.h"
+#include "SkTArray.h"
 #include "SkTDArray.h"
 #include "SkTaskGroup.h"
 #include "SkThreadUtils.h"
 
 #if defined(SK_BUILD_FOR_WIN32)
     static void query_num_cores(int* num_cores) {
         SYSTEM_INFO sysinfo;
         GetNativeSystemInfo(&sysinfo);
         *num_cores = sysinfo.dwNumberOfProcessors;
     }
@@ skipping 14 matching lines @@
 }
 
 namespace {
 
 class ThreadPool : SkNoncopyable {
 public:
     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);
+        gGlobal->add([task]() { task->run(); }, pending);
     }
 
-    static void Add(void (*fn)(void*), void* arg, SkAtomic<int32_t>* pending) {
+    static void Add(std::function<void(void)> fn, SkAtomic<int32_t>* pending) {
         if (!gGlobal) {
-            return fn(arg);
+            return fn();
         }
-        gGlobal->add(fn, arg, pending);
+        gGlobal->add(fn, pending);
     }
 
-    static void Batch(void (*fn)(void*), void* args, int N, size_t stride,
-                      SkAtomic<int32_t>* pending) {
+    static void Batch(std::function<void(int)> fn, int N, SkAtomic<int32_t>* pending) {
         if (!gGlobal) {
-            for (int i = 0; i < N; i++) { fn((char*)args + i*stride); }
+            for (int i = 0; i < N; i++) { fn(i); }
             return;
         }
-        gGlobal->batch(fn, args, N, stride, pending);
+        gGlobal->batch(fn, N, pending);
     }
 
     static void Wait(SkAtomic<int32_t>* pending) {
         if (!gGlobal) {  // If we have no threads, the work must already be done.
             SkASSERT(pending->load(sk_memory_order_relaxed) == 0);
             return;
         }
         // 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;
             {
                 // We're stealing work opportunistically,
                 // so we never call fWorkAvailable.wait(), which could sleep us if there's no work.
                 // This means fWorkAvailable is only an upper bound on fWork.count().
                 AutoLock lock(&gGlobal->fWorkLock);
-                if (gGlobal->fWork.isEmpty()) {
+                if (gGlobal->fWork.empty()) {
                     // 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);
+                work = gGlobal->fWork.back();
+                gGlobal->fWork.pop_back();
             }
             // 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);
+            work.fn();
             work.pending->fetch_add(-1, sk_memory_order_release);  // Pairs with load above.
         }
     }
 
 private:
     struct AutoLock {
         AutoLock(SkSpinlock* lock) : fLock(lock) { fLock->acquire(); }
         ~AutoLock() { fLock->release(); }
     private:
         SkSpinlock* fLock;
     };
 
     static void CallRunnable(void* arg) { static_cast<SkRunnable*>(arg)->run(); }
 
     struct Work {
-        void (*fn)(void*);            // A function to call,
-        void* arg;                    // its argument,
+        std::function<void(void)> fn; // A function to call
         SkAtomic<int32_t>* pending;   // then decrement pending afterwards.
     };
 
     explicit ThreadPool(int threads) {
         if (threads == -1) {
             threads = sk_num_cores();
         }
         for (int i = 0; i < threads; i++) {
             fThreads.push(new SkThread(&ThreadPool::Loop, this));
             fThreads.top()->start();
         }
     }
 
     ~ThreadPool() {
-        SkASSERT(fWork.isEmpty());  // All SkTaskGroups should be destroyed by now.
+        SkASSERT(fWork.empty());  // All SkTaskGroups should be destroyed by now.
 
         // Send a poison pill to each thread.
         SkAtomic<int> dummy(0);
         for (int i = 0; i < fThreads.count(); i++) {
-            this->add(nullptr, nullptr, &dummy);
+            this->add(nullptr, &dummy);

[mtklein, 2015/12/10 20:58:35]

So does nullptr turn into a std::function<void(void)> where operator bool
returns false?  If so, neat.

[herb_g, 2015/12/10 21:58:35]

Yes. Yes it does. I got lucky.

         }
         // Wait for them all to swallow the pill and die.
         for (int i = 0; i < fThreads.count(); i++) {
             fThreads[i]->join();
         }
-        SkASSERT(fWork.isEmpty());  // Can't hurt to double check.
+        SkASSERT(fWork.empty());  // Can't hurt to double check.
         fThreads.deleteAll();
     }
 
-    void add(void (*fn)(void*), void* arg, SkAtomic<int32_t>* pending) {
-        Work work = { fn, arg, pending };
+    void add(std::function<void(void)> fn, SkAtomic<int32_t>* pending) {
+        Work work = { fn, pending };
         pending->fetch_add(+1, sk_memory_order_relaxed);  // No barrier needed.
         {
             AutoLock lock(&fWorkLock);
-            fWork.push(work);
+            fWork.push_back(work);
         }
         fWorkAvailable.signal(1);
     }
 
-    void batch(void (*fn)(void*), void* arg, int N, size_t stride, SkAtomic<int32_t>* pending) {
+    void batch(std::function<void(int)> fn, int N, SkAtomic<int32_t>* pending) {
         pending->fetch_add(+N, sk_memory_order_relaxed);  // No barrier needed.
         {
             AutoLock lock(&fWorkLock);
-            Work* batch = fWork.append(N);
             for (int i = 0; i < N; i++) {
-                Work work = { fn, (char*)arg + i*stride, pending };
-                batch[i] = work;
+                Work work = { [i, fn]() { fn(i); }, pending };
+                fWork.push_back(work);
             }
         }
         fWorkAvailable.signal(N);
     }
 
     static void Loop(void* arg) {
         ThreadPool* pool = (ThreadPool*)arg;
         Work work;
         while (true) {
             // Sleep until there's work available, and claim one unit of Work as we wake.
             pool->fWorkAvailable.wait();
             {
                 AutoLock lock(&pool->fWorkLock);
-                if (pool->fWork.isEmpty()) {
+                if (pool->fWork.empty()) {
                     // Someone in Wait() stole our work (fWorkAvailable is an upper bound).
                     // Well, that's fine, back to sleep for us.
                     continue;
                 }
-                pool->fWork.pop(&work);
+                work = pool->fWork.back();
+                pool->fWork.pop_back();
             }
             if (!work.fn) {
                 return;  // Poison pill.  Time... to die.
             }
-            work.fn(work.arg);
+            work.fn();
             work.pending->fetch_add(-1, sk_memory_order_release);  // Pairs with load in Wait().
         }
     }
 
     // fWorkLock must be held when reading or modifying fWork.
     SkSpinlock      fWorkLock;
-    SkTDArray<Work> fWork;
+    SkTArray<Work>  fWork;
 
     // A thread-safe upper bound for fWork.count().
     //
     // We'd have it be an exact count but for the loop in Wait():
     // we never want that to block, so it can't call fWorkAvailable.wait(),
     // and that's the only way to decrement fWorkAvailable.
     // So fWorkAvailable may overcount actual the work available.
     // We make do, but this means some worker threads may wake spuriously.
     SkSemaphore fWorkAvailable;
 
@@ skipping 14 matching lines @@
         ThreadPool::gGlobal = new ThreadPool(threads);
     }
 }
 
 SkTaskGroup::Enabler::~Enabler() { delete ThreadPool::gGlobal; }
 
 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);
+void SkTaskGroup::add(std::function<void(void)> fn) { ThreadPool::Add(fn, &fPending); }
+void SkTaskGroup::batch (std::function<void(int)> fn, int N) {
+    ThreadPool::Batch(fn, N, &fPending);
 }
 
 int sk_parallel_for_thread_count() {
     if (ThreadPool::gGlobal != nullptr) {
         return ThreadPool::gGlobal->fThreads.count();
     }
     return 0;
 }