Add a simple work queue abstraction.

Makes it easy to schedule a bunch of work to happen in parallel.

Change-Id: Id9c0e52fc8b6d78d2b9ed4c2ee47abce0a01775c

2 files changed, 121 insertions, 0 deletions

diff --git a/include/utils/AndroidThreads.h b/include/utils/AndroidThreads.h
index f9f7aa4..5bda0fd 100644
--- a/include/utils/AndroidThreads.h
+++ b/include/utils/AndroidThreads.h
@@ -73,6 +73,7 @@ extern void androidSetCreateThreadFunc(android_create_thread_fn func);
 // Get pid for the current thread.
 extern pid_t androidGetTid();
 
+#ifdef HAVE_ANDROID_OS
 // Change the scheduling group of a particular thread.  The group
 // should be one of the ANDROID_TGROUP constants.  Returns BAD_VALUE if
 // grp is out of range, else another non-zero value with errno set if
@@ -95,6 +96,7 @@ extern int androidGetThreadPriority(pid_t tid);
 // scheduling groups are disabled.  Returns INVALID_OPERATION if unexpected error.
 // Thread ID zero means current thread.
 extern int androidGetThreadSchedulingGroup(pid_t tid);
+#endif
 
 #ifdef __cplusplus
 } // extern "C"
diff --git a/include/utils/WorkQueue.h b/include/utils/WorkQueue.h
new file mode 100644
index 0000000..e3c75b2
--- /dev/null
+++ b/include/utils/WorkQueue.h
@@ -0,0 +1,119 @@
+/*]
+ * Copyright (C) 2012 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#ifndef _LIBS_UTILS_WORK_QUEUE_H
+#define _LIBS_UTILS_WORK_QUEUE_H
+
+#include <utils/Errors.h>
+#include <utils/Vector.h>
+#include <utils/threads.h>
+
+namespace android {
+
+/*
+ * A threaded work queue.
+ *
+ * This class is designed to make it easy to run a bunch of isolated work
+ * units in parallel, using up to the specified number of threads.
+ * To use it, write a loop to post work units to the work queue, then synchronize
+ * on the queue at the end.
+ */
+class WorkQueue {
+public:
+    class WorkUnit {
+    public:
+        WorkUnit() { }
+        virtual ~WorkUnit() { }
+
+        /*
+         * Runs the work unit.
+         * If the result is 'true' then the work queue continues scheduling work as usual.
+         * If the result is 'false' then the work queue is canceled.
+         */
+        virtual bool run() = 0;
+    };
+
+    /* Creates a work queue with the specified maximum number of work threads. */
+    WorkQueue(size_t maxThreads, bool canCallJava = true);
+
+    /* Destroys the work queue.
+     * Cancels pending work and waits for all remaining threads to complete.
+     */
+    ~WorkQueue();
+
+    /* Posts a work unit to run later.
+     * If the work queue has been canceled or is already finished, returns INVALID_OPERATION
+     * and does not take ownership of the work unit (caller must destroy it itself).
+     * Otherwise, returns OK and takes ownership of the work unit (the work queue will
+     * destroy it automatically).
+     *
+     * For flow control, this method blocks when the size of the pending work queue is more
+     * 'backlog' times the number of threads.  This condition reduces the rate of entry into
+     * the pending work queue and prevents it from growing much more rapidly than the
+     * work threads can actually handle.
+     *
+     * If 'backlog' is 0, then no throttle is applied.
+     */
+    status_t schedule(WorkUnit* workUnit, size_t backlog = 2);
+
+    /* Cancels all pending work.
+     * If the work queue is already finished, returns INVALID_OPERATION.
+     * If the work queue is already canceled, returns OK and does nothing else.
+     * Otherwise, returns OK, discards all pending work units and prevents additional
+     * work units from being scheduled.
+     *
+     * Call finish() after cancel() to wait for all remaining work to complete.
+     */
+    status_t cancel();
+
+    /* Waits for all work to complete.
+     * If the work queue is already finished, returns INVALID_OPERATION.
+     * Otherwise, waits for all work to complete and returns OK.
+     */
+    status_t finish();
+
+private:
+    class WorkThread : public Thread {
+    public:
+        WorkThread(WorkQueue* workQueue, bool canCallJava);
+        virtual ~WorkThread();
+
+    private:
+        virtual bool threadLoop();
+
+        WorkQueue* const mWorkQueue;
+    };
+
+    status_t cancelLocked();
+    bool threadLoop(); // called from each work thread
+
+    const size_t mMaxThreads;
+    const bool mCanCallJava;
+
+    Mutex mLock;
+    Condition mWorkChangedCondition;
+    Condition mWorkDequeuedCondition;
+
+    bool mCanceled;
+    bool mFinished;
+    size_t mIdleThreads;
+    Vector<sp<WorkThread> > mWorkThreads;
+    Vector<WorkUnit*> mWorkUnits;
+};
+
+}; // namespace android
+
+#endif // _LIBS_UTILS_WORK_QUEUE_H