first commit

utils/vp_semaphore.h

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+
+#pragma once
+
+#include <condition_variable>
+#include <mutex>
+
+namespace vp_utils {
+    // semaphore for queue/deque data structures in VideoPipe, used for producer-consumer pattern.
+    // it blocks the consumer thread until data has come.
+    class vp_semaphore
+    {
+    public:
+        vp_semaphore() {
+            count_ = 0;
+        }
+
+        void signal() {
+            std::unique_lock<std::mutex> lock(mutex_);
+            ++count_;
+            cv_.notify_one();
+        }
+
+        void wait() {
+            std::unique_lock<std::mutex> lock(mutex_);
+            cv_.wait(lock, [=] { return count_ > 0; });
+            --count_;
+        }
+        
+        void reset() {
+            std::unique_lock<std::mutex> lock(mutex_);
+            count_ = 0;
+            cv_.notify_one();
+        }
+    private:
+        std::mutex mutex_;
+        std::condition_variable cv_;
+        int count_;
+    };
+}