Make MessageQueue growable

* Uses simple vector resizing (po2)
* Uses pair of read and write buffers

core/local_vector.h

@@ -136,9 +136,11 @@ public:
 		}
 	}
 	_FORCE_INLINE_ bool empty() const { return count == 0; }
-	_FORCE_INLINE_ void reserve(U p_size) {
+	_FORCE_INLINE_ U get_capacity() const { return capacity; }
+
+	_FORCE_INLINE_ void reserve(U p_size, bool p_allow_shrink = false) {
 		p_size = nearest_power_of_2_templated(p_size);
-		if (p_size > capacity) {
+		if (!p_allow_shrink ? p_size > capacity : ((p_size >= count) && (p_size != capacity))) {
 			capacity = p_size;
 			data = (T *)memrealloc(data, capacity * sizeof(T));
 			CRASH_COND_MSG(!data, "Out of memory");

core/message_queue.cpp

@@ -44,17 +44,24 @@ Error MessageQueue::push_call(ObjectID p_id, const StringName &p_method, const V
 
 	int room_needed = sizeof(Message) + sizeof(Variant) * p_argcount;
 
-	if ((buffer_end + room_needed) >= buffer_size) {
+	Buffer &buffer = buffers[write_buffer];
-		String type;
+
-		if (ObjectDB::get_instance(p_id)) {
+	if ((buffer.end + room_needed) > buffer.data.size()) {
-			type = ObjectDB::get_instance(p_id)->get_class();
+		if ((buffer.end + room_needed) > max_allowed_buffer_size) {
+			String type;
+			if (ObjectDB::get_instance(p_id)) {
+				type = ObjectDB::get_instance(p_id)->get_class();
+			}
+			print_line("Failed method: " + p_method);
+			statistics();
+			ERR_FAIL_V_MSG(ERR_OUT_OF_MEMORY, "Message queue out of memory. Try increasing 'memory/limits/message_queue/max_size_mb' in project settings.");
+		} else {
+			buffer.data.resize(buffer.end + room_needed);
 		}
-		print_line("Failed method: " + type + ":" + p_method + " target ID: " + itos(p_id));
-		statistics();
-		ERR_FAIL_V_MSG(ERR_OUT_OF_MEMORY, "Message queue out of memory. Try increasing 'memory/limits/message_queue/max_size_kb' in project settings.");
 	}
 
-	Message *msg = memnew_placement(&buffer[buffer_end], Message);
+	Message *msg = memnew_placement(&buffer.data[buffer.end], Message);
+
 	msg->args = p_argcount;
 	msg->instance_id = p_id;
 	msg->target = p_method;
@@ -63,11 +70,11 @@ Error MessageQueue::push_call(ObjectID p_id, const StringName &p_method, const V
 		msg->type |= FLAG_SHOW_ERROR;
 	}
 
-	buffer_end += sizeof(Message);
+	buffer.end += sizeof(Message);
 
 	for (int i = 0; i < p_argcount; i++) {
-		Variant *v = memnew_placement(&buffer[buffer_end], Variant);
+		Variant *v = memnew_placement(&buffer.data[buffer.end], Variant);
-		buffer_end += sizeof(Variant);
+		buffer.end += sizeof(Variant);
 		*v = *p_args[i];
 	}
 
@@ -94,26 +101,33 @@ Error MessageQueue::push_set(ObjectID p_id, const StringName &p_prop, const Vari
 
 	uint8_t room_needed = sizeof(Message) + sizeof(Variant);
 
-	if ((buffer_end + room_needed) >= buffer_size) {
+	Buffer &buffer = buffers[write_buffer];
-		String type;
+
-		if (ObjectDB::get_instance(p_id)) {
+	if ((buffer.end + room_needed) > buffer.data.size()) {
-			type = ObjectDB::get_instance(p_id)->get_class();
+		if ((buffer.end + room_needed) > max_allowed_buffer_size) {
+			String type;
+			if (ObjectDB::get_instance(p_id)) {
+				type = ObjectDB::get_instance(p_id)->get_class();
+			}
+			print_line("Failed set: " + type + ":" + p_prop + " target ID: " + itos(p_id));
+			statistics();
+			ERR_FAIL_V_MSG(ERR_OUT_OF_MEMORY, "Message queue out of memory. Try increasing 'memory/limits/message_queue/max_size_mb' in project settings.");
+		} else {
+			buffer.data.resize(buffer.end + room_needed);
 		}
-		print_line("Failed set: " + type + ":" + p_prop + " target ID: " + itos(p_id));
-		statistics();
-		ERR_FAIL_V_MSG(ERR_OUT_OF_MEMORY, "Message queue out of memory. Try increasing 'memory/limits/message_queue/max_size_kb' in project settings.");
 	}
 
-	Message *msg = memnew_placement(&buffer[buffer_end], Message);
+	Message *msg = memnew_placement(&buffer.data[buffer.end], Message);
+
 	msg->args = 1;
 	msg->instance_id = p_id;
 	msg->target = p_prop;
 	msg->type = TYPE_SET;
 
-	buffer_end += sizeof(Message);
+	buffer.end += sizeof(Message);
 
-	Variant *v = memnew_placement(&buffer[buffer_end], Variant);
+	Variant *v = memnew_placement(&buffer.data[buffer.end], Variant);
-	buffer_end += sizeof(Variant);
+	buffer.end += sizeof(Variant);
 	*v = p_value;
 
 	return OK;
@@ -126,20 +140,30 @@ Error MessageQueue::push_notification(ObjectID p_id, int p_notification) {
 
 	uint8_t room_needed = sizeof(Message);
 
-	if ((buffer_end + room_needed) >= buffer_size) {
+	Buffer &buffer = buffers[write_buffer];
-		print_line("Failed notification: " + itos(p_notification) + " target ID: " + itos(p_id));
+
-		statistics();
+	if ((buffer.end + room_needed) > buffer.data.size()) {
-		ERR_FAIL_V_MSG(ERR_OUT_OF_MEMORY, "Message queue out of memory. Try increasing 'memory/limits/message_queue/max_size_kb' in project settings.");
+		if ((buffer.end + room_needed) > max_allowed_buffer_size) {
+			String type;
+			if (ObjectDB::get_instance(p_id)) {
+				type = ObjectDB::get_instance(p_id)->get_class();
+			}
+			print_line("Failed notification: " + itos(p_notification) + " target ID: " + itos(p_id));
+			statistics();
+			ERR_FAIL_V_MSG(ERR_OUT_OF_MEMORY, "Message queue out of memory. Try increasing 'memory/limits/message_queue/max_size_mb' in project settings.");
+		} else {
+			buffer.data.resize(buffer.end + room_needed);
+		}
 	}
 
-	Message *msg = memnew_placement(&buffer[buffer_end], Message);
+	Message *msg = memnew_placement(&buffer.data[buffer.end], Message);
 
 	msg->type = TYPE_NOTIFICATION;
 	msg->instance_id = p_id;
 	//msg->target;
 	msg->notification = p_notification;
 
-	buffer_end += sizeof(Message);
+	buffer.end += sizeof(Message);
 
 	return OK;
 }
@@ -161,9 +185,11 @@ void MessageQueue::statistics() {
 	Map<StringName, int> call_count;
 	int null_count = 0;
 
+	Buffer &buffer = buffers[write_buffer];
+
 	uint32_t read_pos = 0;
-	while (read_pos < buffer_end) {
+	while (read_pos < buffer.end) {
-		Message *message = (Message *)&buffer[read_pos];
+		Message *message = (Message *)&buffer.data[read_pos];
 
 		Object *target = ObjectDB::get_instance(message->instance_id);
 
@@ -208,7 +234,7 @@ void MessageQueue::statistics() {
 		}
 	}
 
-	print_line("TOTAL BYTES: " + itos(buffer_end));
+	print_line("TOTAL BYTES: " + itos(buffer.end));
 	print_line("NULL count: " + itos(null_count));
 
 	for (Map<StringName, int>::Element *E = set_count.front(); E; E = E->next()) {
@@ -225,7 +251,8 @@ void MessageQueue::statistics() {
 }
 
 int MessageQueue::get_max_buffer_usage() const {
-	return buffer_max_used;
+	// Note this may be better read_buffer, or a combination, depending when this is read.
+	return buffers[write_buffer].data.size();
 }
 
 void MessageQueue::_call_function(Object *p_target, const StringName &p_func, const Variant *p_args, int p_argcount, bool p_show_error) {
@@ -244,73 +271,135 @@ void MessageQueue::_call_function(Object *p_target, const StringName &p_func, co
 	}
 }
 
-void MessageQueue::flush() {
+void MessageQueue::_update_buffer_monitor() {
-	if (buffer_end > buffer_max_used) {
+	// The number of flushes is an approximate delay before
-		buffer_max_used = buffer_end;
+	// considering shrinking. This is somewhat of a magic number,
+	// but only acts to prevent excessive oscillations.
+	if (++_buffer_size_monitor.flush_count == 8192) {
+		uint32_t max_size = _buffer_size_monitor.max_size;
+
+		// Uncomment this define to log message queue sizes and
+		// auto-shrinking behaviour.
+		// #define GODOT_DEBUG_MESSAGE_QUEUE_SIZES
+#ifdef GODOT_DEBUG_MESSAGE_QUEUE_SIZES
+		print_line("MessageQueue buffer max size " + itos(max_size) + " bytes.");
+#endif
+
+		// reset for next time
+		_buffer_size_monitor.flush_count = 0;
+		_buffer_size_monitor.max_size = 0;
+
+		for (uint32_t n = 0; n < 2; n++) {
+			uint32_t cap = buffers[n].data.get_capacity();
+
+			// Only worry about reducing memory if the capacity is high
+			// (due to e.g. loading a level or something).
+			// The shrinking will only take place below 256K, to prevent
+			// excessive reallocating.
+			if (cap > (256 * 1024)) {
+				// Only shrink if we are routinely using a lot less than the capacity.
+				if ((max_size * 4) < cap) {
+					buffers[n].data.reserve(cap / 2, true);
+#ifdef GODOT_DEBUG_MESSAGE_QUEUE_SIZES
+					print_line("MessageQueue reducing buffer[" + itos(n) + "] capacity from " + itos(cap) + " bytes to " + itos(cap / 2) + " bytes.");
+#endif
+				}
+			}
+		}
 	}
+}
 
-	uint32_t read_pos = 0;
+void MessageQueue::flush() {
-
 	//using reverse locking strategy
 	_THREAD_SAFE_LOCK_
 
-	ERR_FAIL_COND(flushing); //already flushing, you did something odd
+	if (flushing) {
-	flushing = true;
-
-	while (read_pos < buffer_end) {
-		//lock on each iteration, so a call can re-add itself to the message queue
-
-		Message *message = (Message *)&buffer[read_pos];
-
-		uint32_t advance = sizeof(Message);
-		if ((message->type & FLAG_MASK) != TYPE_NOTIFICATION) {
-			advance += sizeof(Variant) * message->args;
-		}
-
-		//pre-advance so this function is reentrant
-		read_pos += advance;
-
 		_THREAD_SAFE_UNLOCK_
-
+		ERR_FAIL_MSG("Already flushing"); //already flushing, you did something odd
-		Object *target = ObjectDB::get_instance(message->instance_id);
-
-		if (target != nullptr) {
-			switch (message->type & FLAG_MASK) {
-				case TYPE_CALL: {
-					Variant *args = (Variant *)(message + 1);
-
-					// messages don't expect a return value
-
-					_call_function(target, message->target, args, message->args, message->type & FLAG_SHOW_ERROR);
-
-				} break;
-				case TYPE_NOTIFICATION: {
-					// messages don't expect a return value
-					target->notification(message->notification);
-
-				} break;
-				case TYPE_SET: {
-					Variant *arg = (Variant *)(message + 1);
-					// messages don't expect a return value
-					target->set(message->target, *arg);
-
-				} break;
-			}
-		}
-
-		if ((message->type & FLAG_MASK) != TYPE_NOTIFICATION) {
-			Variant *args = (Variant *)(message + 1);
-			for (int i = 0; i < message->args; i++) {
-				args[i].~Variant();
-			}
-		}
-
-		message->~Message();
-
-		_THREAD_SAFE_LOCK_
 	}
 
-	buffer_end = 0; // reset buffer
+	// first flip buffers, in preparation
+	SWAP(read_buffer, write_buffer);
+
+	flushing = true;
+	_update_buffer_monitor();
+	_THREAD_SAFE_UNLOCK_
+
+	// This loop works by having a read buffer and write buffer.
+	// While we are reading from one buffer we can be filling another.
+	// This enables them to be independent, and not require locks per message.
+	// It also avoids pushing and resizing the write buffer corrupting the read buffer.
+	// The trade off is that it requires more memory.
+	// However the peak size of each can be lower, because they do not ADD
+	// to each other during transit.
+
+	while (buffers[read_buffer].data.size()) {
+		uint32_t read_pos = 0;
+		Buffer &buffer = buffers[read_buffer];
+
+		while (read_pos < buffer.end) {
+			Message *message = (Message *)&buffer.data[read_pos];
+
+			uint32_t advance = sizeof(Message);
+			if ((message->type & FLAG_MASK) != TYPE_NOTIFICATION) {
+				advance += sizeof(Variant) * message->args;
+			}
+
+			read_pos += advance;
+
+			Object *target = ObjectDB::get_instance(message->instance_id);
+
+			if (target != nullptr) {
+				switch (message->type & FLAG_MASK) {
+					case TYPE_CALL: {
+						Variant *args = (Variant *)(message + 1);
+
+						// messages don't expect a return value
+
+						_call_function(target, message->target, args, message->args, message->type & FLAG_SHOW_ERROR);
+
+					} break;
+					case TYPE_NOTIFICATION: {
+						// messages don't expect a return value
+						target->notification(message->notification);
+
+					} break;
+					case TYPE_SET: {
+						Variant *arg = (Variant *)(message + 1);
+						// messages don't expect a return value
+						target->set(message->target, *arg);
+
+					} break;
+				}
+			}
+
+			if ((message->type & FLAG_MASK) != TYPE_NOTIFICATION) {
+				Variant *args = (Variant *)(message + 1);
+				for (int i = 0; i < message->args; i++) {
+					args[i].~Variant();
+				}
+			}
+
+			message->~Message();
+
+		} // while going through buffer
+
+		buffer.end = 0; // reset buffer
+
+		uint32_t buffer_data_size = buffer.data.size();
+		buffer.data.clear();
+
+		_THREAD_SAFE_LOCK_
+		// keep track of the maximum used size, so we can downsize buffers when appropriate
+		_buffer_size_monitor.max_size = MAX(buffer_data_size, _buffer_size_monitor.max_size);
+
+		// flip buffers, this is the only part that requires a lock
+		SWAP(read_buffer, write_buffer);
+		_THREAD_SAFE_UNLOCK_
+
+	} // while read buffer not empty
+
+	_THREAD_SAFE_LOCK_
 	flushing = false;
 	_THREAD_SAFE_UNLOCK_
 }
@@ -324,34 +413,35 @@ MessageQueue::MessageQueue() {
 	singleton = this;
 	flushing = false;
 
-	buffer_end = 0;
+	max_allowed_buffer_size = GLOBAL_DEF_RST("memory/limits/message_queue/max_size_mb", 32);
-	buffer_max_used = 0;
+	ProjectSettings::get_singleton()->set_custom_property_info("memory/limits/message_queue/max_size_mb", PropertyInfo(Variant::INT, "memory/limits/message_queue/max_size_mb", PROPERTY_HINT_RANGE, "4,512,1,or_greater"));
-	buffer_size = GLOBAL_DEF_RST("memory/limits/message_queue/max_size_kb", DEFAULT_QUEUE_SIZE_KB);
+
-	ProjectSettings::get_singleton()->set_custom_property_info("memory/limits/message_queue/max_size_kb", PropertyInfo(Variant::INT, "memory/limits/message_queue/max_size_kb", PROPERTY_HINT_RANGE, "1024,4096,1,or_greater"));
+	max_allowed_buffer_size *= 1024 * 1024;
-	buffer_size *= 1024;
-	buffer = memnew_arr(uint8_t, buffer_size);
 }
 
 MessageQueue::~MessageQueue() {
-	uint32_t read_pos = 0;
+	for (int which = 0; which < 2; which++) {
+		Buffer &buffer = buffers[which];
+		uint32_t read_pos = 0;
 
-	while (read_pos < buffer_end) {
+		while (read_pos < buffer.end) {
-		Message *message = (Message *)&buffer[read_pos];
+			Message *message = (Message *)&buffer.data[read_pos];
-		Variant *args = (Variant *)(message + 1);
+			Variant *args = (Variant *)(message + 1);
-		int argc = message->args;
+			int argc = message->args;
-		if ((message->type & FLAG_MASK) != TYPE_NOTIFICATION) {
+			if ((message->type & FLAG_MASK) != TYPE_NOTIFICATION) {
-			for (int i = 0; i < argc; i++) {
+				for (int i = 0; i < argc; i++) {
-				args[i].~Variant();
+					args[i].~Variant();
+				}
+			}
+			message->~Message();
+
+			read_pos += sizeof(Message);
+			if ((message->type & FLAG_MASK) != TYPE_NOTIFICATION) {
+				read_pos += sizeof(Variant) * message->args;
 			}
 		}
-		message->~Message();
 
-		read_pos += sizeof(Message);
+	} // for which
-		if ((message->type & FLAG_MASK) != TYPE_NOTIFICATION) {
-			read_pos += sizeof(Variant) * message->args;
-		}
-	}
 
 	singleton = nullptr;
-	memdelete_arr(buffer);
 }

core/message_queue.h

@@ -31,16 +31,13 @@
 #ifndef MESSAGE_QUEUE_H
 #define MESSAGE_QUEUE_H
 
+#include "core/local_vector.h"
 #include "core/object.h"
 #include "core/os/thread_safe.h"
 
 class MessageQueue {
 	_THREAD_SAFE_CLASS_
 
-	enum {
-		DEFAULT_QUEUE_SIZE_KB = 4096
-	};
-
 	enum {
 		TYPE_CALL,
 		TYPE_NOTIFICATION,
@@ -60,12 +57,23 @@ class MessageQueue {
 		};
 	};
 
-	uint8_t *buffer;
+	struct Buffer {
-	uint32_t buffer_end;
+		LocalVector<uint8_t> data;
-	uint32_t buffer_max_used;
+		uint64_t end = 0;
-	uint32_t buffer_size;
+	};
+
+	Buffer buffers[2];
+	int read_buffer = 0;
+	int write_buffer = 1;
+	uint64_t max_allowed_buffer_size = 0;
+
+	struct BufferSizeMonitor {
+		uint32_t max_size = 0;
+		uint32_t flush_count = 0;
+	} _buffer_size_monitor;
 
 	void _call_function(Object *p_target, const StringName &p_func, const Variant *p_args, int p_argcount, bool p_show_error);
+	void _update_buffer_monitor();
 
 	static MessageQueue *singleton;
 

doc/classes/ProjectSettings.xml

@@ -1190,7 +1190,7 @@
 		</member>
 		<member name="memory/limits/command_queue/multithreading_queue_size_kb" type="int" setter="" getter="" default="256">
 		</member>
-		<member name="memory/limits/message_queue/max_size_kb" type="int" setter="" getter="" default="4096">
+		<member name="memory/limits/message_queue/max_size_mb" type="int" setter="" getter="" default="32">
 			Godot uses a message queue to defer some function calls. If you run out of space on it (you will see an error), you can increase the size here.
 		</member>
 		<member name="memory/limits/multithreaded_server/rid_pool_prealloc" type="int" setter="" getter="" default="60">