libcamera/base: Move extended base functionality

Move the functionality for the following components to the new
base support library:

 - BoundMethod
 - EventDispatcher
 - EventDispatcherPoll
 - Log
 - Message
 - Object
 - Signal
 - Semaphore
 - Thread
 - Timer

While it would be preferable to see these split to move one component
per commit, these components are all interdependent upon each other,
which leaves us with one big change performing the move for all of them.

Reviewed-by: Hirokazu Honda <hiroh@chromium.org>
Reviewed-by: Paul Elder <paul.elder@ideasonboard.com>
Signed-off-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

1 files changed, 103 insertions, 0 deletions

diff --git a/src/libcamera/base/semaphore.cpp b/src/libcamera/base/semaphore.cpp
new file mode 100644
index 00000000..7aedc6a8
--- /dev/null
+++ b/src/libcamera/base/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 <libcamera/base/semaphore.h>
+#include <libcamera/base/thread.h>
+
+/**
+ * \file base/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 */