#2787: add queueSize property to the AsyncChannel

Foundation/include/Poco/AsyncChannel.h

@@ -82,6 +82,20 @@ public:
 		///    * highest
 		///
 		/// The "priority" property is set-only.
+		///
+		/// The "queueSize" property allows to limit the number
+		/// of messages in the queue. If the queue is full and
+		/// new messages are logged, these are dropped until the
+		/// queue has free capacity again. The number of dropped
+		/// messages is recorded, and a log message indicating the
+		/// number of dropped messages will be generated when the
+		/// queue has free capacity again.
+		/// In addition to an unsigned integer specifying the size,
+		/// this property can have the values "none" or "unlimited",
+		/// which disable the queue size limit. A size of 0 also
+		/// removes the limit.
+		///
+		/// The "queueSize" property is set-only.
 
 protected:
 	~AsyncChannel();
@@ -94,6 +108,8 @@ private:
 	FastMutex _threadMutex;
 	FastMutex _channelMutex;
 	NotificationQueue _queue;
+	std::size_t _queueSize = 0;
+	std::size_t _dropCount = 0;
 };
 
 

Foundation/src/AsyncChannel.cpp

@@ -18,7 +18,10 @@
 #include "Poco/Formatter.h"
 #include "Poco/AutoPtr.h"
 #include "Poco/LoggingRegistry.h"
+#include "Poco/NumberParser.h"
 #include "Poco/Exception.h"
+#include "Poco/String.h"
+#include "Poco/Format.h"
 
 
 namespace Poco {
@@ -106,6 +109,18 @@ void AsyncChannel::close()
 
 void AsyncChannel::log(const Message& msg)
 {
+	if (_queueSize != 0 && _queue.size() >= _queueSize)
+	{
+		++_dropCount;
+		return;
+	}
+
+	if (_dropCount != 0)
+	{
+		_queue.enqueueNotification(new MessageNotification(Message(msg, Poco::format("Dropped %z messages.", _dropCount))));
+		_dropCount = 0;
+	}
+
 	open();
 
 	_queue.enqueueNotification(new MessageNotification(msg));
@@ -115,11 +130,24 @@ void AsyncChannel::log(const Message& msg)
 void AsyncChannel::setProperty(const std::string& name, const std::string& value)
 {
 	if (name == "channel")
+	{
 		setChannel(LoggingRegistry::defaultRegistry().channelForName(value));
+	}
 	else if (name == "priority")
+	{
 		setPriority(value);
+	}
+	else if (name == "queueSize")
+	{
+		if (Poco::icompare(value, "none") == 0 || Poco::icompare(value, "unlimited") == 0 || value.empty())
+			_queueSize = 0;
 		else
+			_queueSize = Poco::NumberParser::parseUnsigned(value);
+	}
+	else
+	{
 		Channel::setProperty(name, value);
+	}
 }