[libcamera-devel] [PATCH 3/6] libcamera: object: Add ObjectConditionVariable class

[Jacopo Mondi]

Add ObjectConditionVariable class that implements an Object
synchronization primitive used to synchronize message delivery between
Object running in different execution contexts.

Signed-off-by: Jacopo Mondi <jacopo at jmondi.org>
---
 include/libcamera/object.h | 19 ++++++++++++++++
 src/libcamera/object.cpp   | 46 ++++++++++++++++++++++++++++++++++++++
 2 files changed, 65 insertions(+)

diff --git a/include/libcamera/object.h b/include/libcamera/object.h
index be07611c25c6..c6477f18417d 100644
--- a/include/libcamera/object.h
+++ b/include/libcamera/object.h
@@ -7,8 +7,10 @@
 #ifndef __LIBCAMERA_OBJECT_H__
 #define __LIBCAMERA_OBJECT_H__
 
+#include <condition_variable>
 #include <list>
 #include <memory>
+#include <mutex>
 #include <vector>
 
 #include <libcamera/bound_method.h>
@@ -28,6 +30,23 @@ enum InvocationType {
 	InvocationTypeBlocking,
 };
 
+class ObjectConditionVariable
+{
+public:
+	ObjectConditionVariable()
+		: delivered_(false)
+	{
+	}
+
+	void notifyReception();
+	void waitDelivery();
+
+private:
+	std::condition_variable cv_;
+	std::mutex mutex_;
+	bool delivered_;
+};
+
 class Object
 {
 public:
diff --git a/src/libcamera/object.cpp b/src/libcamera/object.cpp
index d7c9ac970d1c..88054aba3454 100644
--- a/src/libcamera/object.cpp
+++ b/src/libcamera/object.cpp
@@ -52,6 +52,52 @@ LOG_DEFINE_CATEGORY(Object)
  * the called method is not executed
  */
 
+/**
+ * \class ObjectConditionVariable
+ * \brief Object synchronization primitive that wraps a std::condition_variable
+ *
+ * The ObjectConditionVariable class provides an object synchronization
+ * primitive to synchronize Object running in different execution context.
+ *
+ * It wraps an std::condition_variable that protects a shared variable.
+ *
+ * The class is used to implement blocking message delivery between Object
+ * instances running in different execution context.
+ */
+
+/**
+ * \fn ObjectConditionVariable::ObjectConditionVariable()
+ * \brief Create an ObjectConditionVariable with the shared variable initialized
+ * to false
+ */
+
+/**
+ * \brief Notify the ObjectConditionVariable to signal message reception
+ */
+void ObjectConditionVariable::notifyReception()
+{
+	{
+		MutexLocker locker(mutex_);
+		delivered_ = true;
+	}
+	cv_.notify_one();
+}
+
+/**
+ * \brief Wait for the ObjectConditionVariable to be signaled
+ *
+ * Wait for the ObjectConditionVariable to be signaled by suspending the Object
+ * on the wrapped std::condition_variable. If the shared condition
+ * variable has already been set to true by the Object that was meant to
+ * signal the ObjectConditionVariable before waitDelivery() is invoked,
+ * the operation returns immediately.
+ */
+void ObjectConditionVariable::waitDelivery()
+{
+	MutexLocker locker(mutex_);
+	cv_.wait(locker, [&] { return delivered_; });
+}
+
 /**
  * \class Object
  * \brief Base object to support automatic signal disconnection
-- 
2.23.0