Add SkThreadPool for managing threads.

Skia-ized from https://codereview.appspot.com/6755043/

TODO: Use SkThread and platform independent features.

Review URL: https://codereview.appspot.com/6777064

git-svn-id: http://skia.googlecode.com/svn/trunk@6217 2bbb7eff-a529-9590-31e7-b0007b416f81

1 files changed, 88 insertions, 0 deletions

diff --git a/src/utils/SkThreadPool.cpp b/src/utils/SkThreadPool.cpp
new file mode 100644
index 0000000000..78cb417d07
--- /dev/null
+++ b/src/utils/SkThreadPool.cpp
@@ -0,0 +1,88 @@
+/*
+ * Copyright 2012 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkThreadPool.h"
+#include "SkRunnable.h"
+#include "SkThreadUtils.h"
+
+SkThreadPool::SkThreadPool(const int count)
+: fDone(false) {
+    // Create count threads, all running SkThreadPool::Loop.
+    for (int i = 0; i < count; i++) {
+        SkThread* thread = SkNEW_ARGS(SkThread, (&SkThreadPool::Loop, this));
+        *fThreads.append() = thread;
+        thread->start();
+    }
+}
+
+SkThreadPool::~SkThreadPool() {
+    fDone = true;
+    fReady.lock();
+    fReady.broadcast();
+    fReady.unlock();
+
+    // Wait for all threads to stop.
+    for (int i = 0; i < fThreads.count(); i++) {
+        fThreads[i]->join();
+        SkDELETE(fThreads[i]);
+    }
+}
+
+/*static*/ void SkThreadPool::Loop(void* arg) {
+    // The SkThreadPool passes itself as arg to each thread as they're created.
+    SkThreadPool* pool = static_cast<SkThreadPool*>(arg);
+
+    while (true) {
+        // We have to be holding the lock to read the queue and to call wait.
+        pool->fReady.lock();
+        while(pool->fQueue.isEmpty()) {
+            // Is it time to die?
+            if (pool->fDone) {
+                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.tail();
+
+        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->fReady.unlock();
+
+        // OK, now really do the work.
+        r->fRunnable->run();
+        SkDELETE(r);
+    }
+
+    SkASSERT(false); // Unreachable.  The only exit happens when pool->fDone.
+}
+
+void SkThreadPool::add(SkRunnable* r) {
+    if (NULL == r) {
+        return;
+    }
+
+    // If we don't have any threads, obligingly just run the thing now.
+    if (fThreads.isEmpty()) {
+        return r->run();
+    }
+
+    // We have some threads.  Queue it up!
+    fReady.lock();
+    LinkedRunnable* linkedRunnable = SkNEW(LinkedRunnable);
+    linkedRunnable->fRunnable = r;
+    fQueue.addToHead(linkedRunnable);
+    fReady.signal();
+    fReady.unlock();
+}