Add support for multi-threaded execution of time invariant stages of a stream

Charles Otto
1 parent 14026845
Showing 1 changed file with 142 additions and 30 deletions
sdk/plugins/stream.cpp
@@ -2,6 +2,8 @@
 #include <QReadWriteLock>
 #include <QWaitCondition>
 #include <QThreadPool>
+#include <QSemaphore>
+#include <QMap>
 #include "core/common.h"
 #include "core/opencvutils.h"
@@ -38,7 +40,7 @@ public:
     virtual void startInput() = 0;
 };
-// For 1 - 1 boundaries, a buffer class with a single shared buffer, a mutex
+// For 1 - n boundaries, a buffer class with a single shared buffer, a mutex
 // is used to serialize all access to the buffer.
 class SingleBuffer : public SharedBuffer
 {
@@ -98,6 +100,85 @@ private:
     QList<FrameData *> buffer;
 };
+// for n - 1 boundaries, multiple threads call addItem, the frames are
+// sequenced based on FrameData::sequence_number, and calls to getItem
+// receive them in that order
+class SequencingBuffer : public SharedBuffer
+{
+public:
+    SequencingBuffer()
+    {
+        no_input = false;
+        next_target = 0;
+    }
+
+    void stoppedInput()
+    {
+        QMutexLocker bufferLock(&bufferGuard);
+        no_input = true;
+        // Release anything waiting for input items.
+        availableInput.wakeAll();
+    }
+
+    // There will be more input
+    void startInput()
+    {
+        QMutexLocker bufferLock(&bufferGuard);
+        no_input = false;
+    }
+
+    void addItem(FrameData * input)
+    {
+        QMutexLocker bufferLock(&bufferGuard);
+
+        buffer.insert(input->sequenceNumber, input);
+
+        if (input->sequenceNumber == next_target) {
+            availableInput.wakeOne();
+        }
+    }
+
+    FrameData * getItem()
+    {
+        QMutexLocker bufferLock(&bufferGuard);
+
+        if (buffer.empty() || buffer.begin().key() != this->next_target) {
+            if (buffer.empty() && no_input) {
+                next_target = 0;
+                return NULL;
+            }
+            availableInput.wait(&bufferGuard);
+        }
+
+        // availableInput was signalled, but the buffer is empty? We're done here.
+        if (buffer.empty()) {
+            next_target = 0;
+            return NULL;
+        }
+
+        QMap<int, FrameData *>::Iterator result = buffer.begin();
+        //next_target++;
+        if (next_target != result.value()->sequenceNumber) {
+            qWarning("mismatched targets!");
+        }
+
+        next_target = next_target + 1;
+
+        FrameData * output = result.value();
+        buffer.erase(result);
+        return output;
+    }
+
+private:
+    QMutex bufferGuard;
+    QWaitCondition availableInput;
+    bool no_input;
+
+    int next_target;
+
+    QMap<int, FrameData *> buffer;
+};
+
 // For 1 - 1 boundaries, a double buffering scheme
 // Producer/consumer read/write from separate buffers, and switch if their
 // buffer runs out/overflows. Synchronization is handled by a read/write lock
@@ -372,7 +453,6 @@ public:
         if (input.empty()) {
             actualSource = new VideoDataSource(0);
             open_res = actualSource->open(input);
-            qDebug("created video resource status %d", open_res);
         }
         else {
             // create frame dealer
@@ -402,37 +482,32 @@ class ProcessingStage : public QRunnable
 {
     friend class StreamTransform;
 public:
-    ProcessingStage()
+    ProcessingStage(int nThreads = 1)
     {
+        thread_count = nThreads;
+        activeThreads.release(thread_count);
         setAutoDelete(false);
     }
     void markStart()
     {
-        QMutexLocker lock(&stoppedGuard);
-        stopped = false;
+        activeThreads.acquire();
     }
     void waitStop()
     {
-        stoppedGuard.lock();
-        while (!stopped)
-        {
-            waitStopped.wait(&stoppedGuard);
-        }
-        stoppedGuard.unlock();
+        // Wait until all threads have stopped
+        activeThreads.acquire(thread_count);
+        activeThreads.release(thread_count);
     }
 protected:
     void markStop()
     {
-        QMutexLocker lock(&stoppedGuard);
-        stopped = true;
-        this->waitStopped.wakeAll();
+        activeThreads.release();
     }
-    QMutex stoppedGuard;
-    QWaitCondition waitStopped;
-    bool stopped;
+    QSemaphore activeThreads;
+    int thread_count;
     SharedBuffer * inputBuffer;
     SharedBuffer * outputBuffer;
@@ -443,6 +518,7 @@ public:
     // We should start, and enter a wait on input data
     void run()
     {
+        markStart();
         forever
         {
             FrameData * currentItem = inputBuffer->getItem();
@@ -455,9 +531,9 @@ public:
         }
         markStop();
     }
-
 };
+
 // No input buffer, instead we draw templates from some data source
 // Will be operated by the main thread for the stream
 class FirstStage : public ProcessingStage
@@ -511,6 +587,7 @@ public:
 class StreamTransform : public CompositeTransform
 {
     Q_OBJECT
+    int threads_per_multi_stage;
 public:
     void train(const TemplateList & data)
     {
@@ -558,12 +635,11 @@ public:
         // Start our processing stages
         for (int i=0; i < this->processingStages.size(); i++) {
-            processingStages[i]->markStart();
-            processingThreads.start(processingStages[i]);
+            int count = stage_variance[i] ? 1 : threads_per_multi_stage;
+            for (int j =0; j < count; j ++) processingThreads.start(processingStages[i]);
         }
         // Start the final stage
-        collectionStage.markStart();
         processingThreads.start(&collectionStage);
         // Run the read stage ourselves
@@ -597,18 +673,28 @@ public:
     // Create and link stages
     void init()
     {
-        // Set up the thread pool, 1 stage for each transform, as well as first
-        // and last stages, but the first stage is operated by the thread that
-        // calls project so the pool only needs nTransforms+1 total.
-        processingThreads.setMaxThreadCount(transforms.size() + 1);
-
+        int thread_count = 0;
+        threads_per_multi_stage = 4;
         stage_variance.reserve(transforms.size());
         foreach (const br::Transform *transform, transforms) {
             stage_variance.append(transform->timeVarying());
+            thread_count += transform->timeVarying() ? 1 : threads_per_multi_stage;
         }
-        // buffer 0 -- output buffer for the read stage
-        sharedBuffers.append(new DoubleBuffer());
+        // Set up the thread pool, 1 stage for each transform, as well as first
+        // and last stages, but the first stage is operated by the thread that
+        // calls project so the pool only needs nTransforms+1 total.
+        processingThreads.setMaxThreadCount(thread_count + 1);
+
+
+        // buffer 0 -- output buffer for the read stage, input buffer for
+        // first transform. Is that transform time-varying?
+        if (stage_variance[0])
+            sharedBuffers.append(new DoubleBuffer());
+        // If not, we can run multiple threads
+        else
+            sharedBuffers.append(new SingleBuffer());
+
         readStage.outputBuffer = sharedBuffers.last();
         readStage.stage_id = 0;
@@ -618,13 +704,39 @@ public:
         for (int i =0; i < transforms.size(); i++)
         {
             // Set up this stage
-            processingStages.append(new ProcessingStage());
+            processingStages.append(new ProcessingStage(stage_variance[i] ? 1 : threads_per_multi_stage));
             processingStages.last()->stage_id = next_stage_id++;
             processingStages.last()->inputBuffer = sharedBuffers[lastBufferIdx];
             lastBufferIdx++;
-            sharedBuffers.append(new DoubleBuffer());
+            // This stage's output buffer, next stage's input buffer. If this is
+            // the last transform, the next stage is the (time varying) collection
+            // stage
+            bool next_variance = (i+1) < transforms.size() ? stage_variance[i+1] : true;
+            bool current_variance = stage_variance[i];
+            // if this is a single threaded stage
+            if (current_variance)
+            {
+                // 1 - 1 case
+                if (next_variance)
+                    sharedBuffers.append(new DoubleBuffer());
+                // 1 - n case
+                else
+                    sharedBuffers.append(new SingleBuffer());
+            }
+            // This is a multi-threaded stage
+            else
+            {
+                // If the next stage is single threaded, we need to sequence our
+                // output (n - 1 case)
+                if (next_variance)
+                    sharedBuffers.append(new SequencingBuffer());
+                // Otherwise, this is an n-n boundary and we don't need to
+                // adhere to any particular sequence
+                else
+                    sharedBuffers.append(new SingleBuffer());
+            }
             processingStages.last()->outputBuffer = sharedBuffers.last();
             processingStages.last()->transform = transforms[i];
         }