bugs in dispatch queue creation

[jrmaxdev]

Creating a dispatch queue with dispatch_queue_create requires an attr param.
This attribute can be created with dispatch_queue_attr_make_with_qos_class.
This function takes a relative_priority as third parameter.

dispatch_queue_attr_make_with_qos_class is used in three MIKMIDI source files:

MIKMIDIClock.m
MIKMIDISequencer.m
MIKMIDISynthesizer.m

In all cases DISPATCH_QUEUE_PRIORITY_HIGH is assigned to it.

It is defined to be 2 (<queue.h>)
#define DISPATCH_QUEUE_PRIORITY_HIGH 2

This assignment leads to a NULL result and a standard serial queue will be created.

From the Dispatch framework documentation:

relative_priority
A negative offset from the maximum supported scheduler priority for the given quality-of-service class. This value must be less than 0 and greater than or equal to QOS_MIN_RELATIVE_PRIORITY, or else this function returns NULL.

To assign a quality of service class to the queue and achieve maximum priority in relation to it the value should be 0.

attr = dispatch_queue_attr_make_with_qos_class(DISPATCH_QUEUE_SERIAL, QOS_CLASS_USER_INTERACTIVE, 0);

or

attr = dispatch_queue_attr_make_with_qos_class(DISPATCH_QUEUE_SERIAL, QOS_CLASS_USER_INITIATED, 0);