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authorLaurent Pinchart <laurent.pinchart@ideasonboard.com>2019-10-28 04:14:52 +0200
committerLaurent Pinchart <laurent.pinchart@ideasonboard.com>2019-10-28 17:11:40 +0200
commit66e7c5b774e288faa3a9b413861d6a77723db3ad (patch)
treef815ad41d84a2994bef141b4e8484cb939872219 /src
parent448716d8f75185795d9b01164440d0753850a80a (diff)
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>
Diffstat (limited to 'src')
-rw-r--r--src/libcamera/include/meson.build1
-rw-r--r--src/libcamera/include/semaphore.h34
-rw-r--r--src/libcamera/meson.build1
-rw-r--r--src/libcamera/semaphore.cpp103
4 files changed, 139 insertions, 0 deletions
diff --git a/src/libcamera/include/meson.build b/src/libcamera/include/meson.build
index 2c74d29b..64c2155f 100644
--- a/src/libcamera/include/meson.build
+++ b/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',
diff --git a/src/libcamera/include/semaphore.h b/src/libcamera/include/semaphore.h
new file mode 100644
index 00000000..c6b28653
--- /dev/null
+++ b/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__ */
diff --git a/src/libcamera/meson.build b/src/libcamera/meson.build
index f201f408..afbca769 100644
--- a/src/libcamera/meson.build
+++ b/src/libcamera/meson.build
@@ -28,6 +28,7 @@ libcamera_sources = files([
'pixelformats.cpp',
'process.cpp',
'request.cpp',
+ 'semaphore.cpp',
'signal.cpp',
'stream.cpp',
'thread.cpp',
diff --git a/src/libcamera/semaphore.cpp b/src/libcamera/semaphore.cpp
new file mode 100644
index 00000000..ce1eae49
--- /dev/null
+++ b/src/libcamera/semaphore.cpp
@@ -0,0 +1,103 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+/*
+ * Copyright (C) 2019, Google Inc.
+ *
+ * semaphore.cpp - General-purpose counting semaphore
+ */
+
+#include "semaphore.h"
+#include "thread.h"
+
+/**
+ * \file semaphore.h
+ * \brief General-purpose counting semaphore
+ */
+
+namespace libcamera {
+
+/**
+ * \class Semaphore
+ * \brief General-purpose counting semaphore
+ *
+ * A semaphore is a locking primitive that protects resources. It is created
+ * with an initial number of resources (which may be 0), and offers two
+ * primitives to acquire and release resources. The acquire() method tries to
+ * acquire a number of resources, and blocks if not enough resources are
+ * available until they get released. The release() method releases a number of
+ * resources, waking up any consumer blocked on an acquire() call.
+ */
+
+/**
+ * \brief Construct a semaphore with \a n resources
+ * \param[in] n The resource count
+ */
+Semaphore::Semaphore(unsigned int n)
+ : available_(n)
+{
+}
+
+/**
+ * \brief Retrieve the number of available resources
+ * \return The number of available resources
+ */
+unsigned int Semaphore::available()
+{
+ MutexLocker locker(mutex_);
+ return available_;
+}
+
+/**
+ * \brief Acquire \a n resources
+ * \param[in] n The resource count
+ *
+ * This method attempts to acquire \a n resources. If \a n is higher than the
+ * number of available resources, the call will block until enough resources
+ * become available.
+ */
+void Semaphore::acquire(unsigned int n)
+{
+ MutexLocker locker(mutex_);
+ cv_.wait(locker, [&] { return available_ >= n; });
+ available_ -= n;
+}
+
+/**
+ * \brief Try to acquire \a n resources without blocking
+ * \param[in] n The resource count
+ *
+ * This method attempts to acquire \a n resources. If \a n is higher than the
+ * number of available resources, it returns false immediately without
+ * acquiring any resource. Otherwise it acquires the resources and returns
+ * true.
+ *
+ * \return True if the resources have been acquired, false otherwise
+ */
+bool Semaphore::tryAcquire(unsigned int n)
+{
+ MutexLocker locker(mutex_);
+ if (available_ < n)
+ return false;
+
+ available_ -= n;
+ return true;
+}
+
+/**
+ * \brief Release \a n resources
+ * \param[in] n The resource count
+ *
+ * This method releases \a n resources, increasing the available resource count
+ * by \a n. If the number of available resources becomes large enough for any
+ * consumer blocked on an acquire() call, those consumers get woken up.
+ */
+void Semaphore::release(unsigned int n)
+{
+ {
+ MutexLocker locker(mutex_);
+ available_ += n;
+ }
+
+ cv_.notify_all();
+}
+
+} /* namespace libcamera */