adding a simple queue needed for the media server's handling of notifications

git-svn-id: file:///srv/svn/repos/haiku/trunk/current@1298 a95241bf-73f2-0310-859d-f6bbb57e9c96

src/servers/media/Jamfile

@@ -7,5 +7,6 @@ Server media_server :
 	AppManager.cpp
 	BufferManager.cpp
 	NodeManager.cpp
+	Queue.cpp
 ;
 LinkSharedOSLibs media_server : be libmedia.so root ;

src/servers/media/Queue.cpp

@@ -0,0 +1,91 @@
+/* 
+ * Copyright 2002, Marcus Overhagen. All rights reserved.
+ * Distributed under the terms of the MIT License.
+ */
+/* This is a simple multi thread save queue.
+ *
+ * One thread calls AddItem() to add items, and when it
+ * is finished doing so, it calls Terminate(). Another
+ * thread calls RemoveItem() to remove items from the
+ * queue. RemoveItem() blocks when no items are available.
+ * As soon as Terminate() is called and the queue is empty,
+ * RemoveItem() returns NULL.
+ */
+ 
+#include <List.h>
+#include <OS.h>
+#include <Locker.h>
+
+#include "Queue.h"
+
+Queue::Queue()
+ :	fList(new BList),
+	fLocker(new BLocker),
+	fSem(create_sem(0,"queue sem"))
+{
+}
+
+Queue::~Queue()
+{
+	if (fSem > 0)
+		delete_sem(fSem);
+	delete fLocker;
+	delete fList;
+}
+
+status_t
+Queue::Terminate()
+{
+	status_t rv;
+
+	fLocker->Lock();
+	if (fSem < 0) {
+		rv = B_ERROR;
+	} else {
+		delete_sem(fSem);
+		fSem = -1;
+		rv = B_OK;
+	}
+	fLocker->Unlock();
+	return rv;
+}
+	
+status_t
+Queue::AddItem(void *item)
+{
+	status_t rv;
+
+	fLocker->Lock();
+	if (fSem < 0) {
+		rv = B_ERROR;
+	} else {
+		if (B_OK == fList->AddItem(item)) {
+			release_sem(fSem);
+			rv = B_OK;
+		} else {
+			rv = B_ERROR;
+		}
+	}
+	fLocker->Unlock();
+	return rv;
+}
+
+void *
+Queue::RemoveItem()
+{
+	status_t rv;
+	void *item;
+
+	// if the semaphore is deleted by Terminate(),
+	// this will no longer block
+	while (acquire_sem(fSem) == B_INTERRUPTED)
+		;
+	
+	// if the list is empty, which can only happen after
+	// Terminate() was called, item will be NULL
+	fLocker->Lock();
+	item = fList->RemoveItem((int32)0);
+	fLocker->Unlock();
+	
+	return item;	
+}

src/servers/media/Queue.h

@@ -0,0 +1,21 @@
+/* 
+ * Copyright 2002, Marcus Overhagen. All rights reserved.
+ * Distributed under the terms of the MIT License.
+ */
+
+class Queue
+{
+public:
+	Queue();
+	~Queue();
+
+	status_t	Terminate();
+	
+	status_t	AddItem(void *item);
+	void *		RemoveItem();
+	
+private:
+	BList		*fList;
+	BLocker		*fLocker;
+	sem_id		fSem;
+};