libcamera: Add Semaphore class

Add a general-purpose counting semaphore class.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Niklas Söderlund <niklas.soderlund@ragnatech.se>

src/libcamera/include/meson.build

@@ -17,6 +17,7 @@ libcamera_headers = files([
     'message.h',
     'pipeline_handler.h',
     'process.h',
+    'semaphore.h',
     'thread.h',
     'utils.h',
     'v4l2_controls.h',

src/libcamera/include/semaphore.h

@@ -0,0 +1,34 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2019, Google Inc.
+ *
+ * semaphore.h - General-purpose counting semaphore
+ */
+#ifndef __LIBCAMERA_SEMAPHORE_H__
+#define __LIBCAMERA_SEMAPHORE_H__
+
+#include <condition_variable>
+
+#include "thread.h"
+
+namespace libcamera {
+
+class Semaphore
+{
+public:
+	Semaphore(unsigned int n = 0);
+
+	unsigned int available();
+	void acquire(unsigned int n = 1);
+	bool tryAcquire(unsigned int n = 1);
+	void release(unsigned int n = 1);
+
+private:
+	Mutex mutex_;
+	std::condition_variable cv_;
+	unsigned int available_;
+};
+
+} /* namespace libcamera */
+
+#endif /* __LIBCAMERA_SEMAPHORE_H__ */