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Asked: 2026-05-22T02:34:48+00:00

I am struggling with a deadlock in my GCD code. Then I saw this

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I am struggling with a deadlock in my GCD code. Then I saw this function dispatch_debug in the header file <dispatch/object.h>.

/*!
 * @function dispatch_debug
 *
 * @abstract
 * Programmatically log debug information about a dispatch object.
 *
 * @param object
 * The object to introspect.
 *
 * @param message
 * The message to log above and beyond the introspection.
 */
__OSX_AVAILABLE_STARTING(__MAC_10_6,__IPHONE_4_0)
DISPATCH_EXPORT DISPATCH_NONNULL2 DISPATCH_NOTHROW __attribute__((__format__(printf,2,3)))
void
dispatch_debug(dispatch_object_t object, const char *message, ...);

But I am not able to make it do anything. I was hoping it would print out the state and locks or something like that.

Here is how I use it:

grabber_queue = dispatch_queue_create("com.unpaq.tvguideplus.grabber", NULL);
dispatch_debug(grabber_queue, "grabber queue");
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1 Answer

  1. Editorial Team

    dispatch_debug

    Debug information is logged to the Console log. This information can be useful as a debugging tool to view the internal state (current reference count, suspension count, etc.) of a dispatch object at the time the dispatch_debug function is called.

    dispatch_debug sends messages to syslog. So,

    grabber_queue = dispatch_queue_create("com.unpaq.tvguideplus.grabber", NULL);
dispatch_debug(grabber_queue, "grabber queue");

    this code would print as the following in system.log.

    May 13 08:50:17 hostname exefile[53164]: com.unpaq.tvguideplus.grabber[0x6200e10] = {
 xrefcnt = 0x1, refcnt = 0x1, suspend_cnt = 0x0, locked = 0, target =
 com.apple.root.default-overcommit-priority[0x1af0700], width = 0x0, running = 0x0,
 barrier = 0 }: grabber queueMay

    It doesn’t appear in Xcode debug console. You can see in /Applications/Utilities/Console.app system.log on the iPhone simulator, or in Xcode organizer on iPhone, iPod touch and iPad.

    By the way, GCD is open source. It is distributed via libdispatch. dispatch_debug is included in src/object.c.

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