[libdispatch-dev] Block not released after dispatch_source_set_event_handler

[Allan Odgaard]

I am seeing an issue where the block given to dispatch_source_set_event_handler appear not to be released when a new handler is set.

If I build and run the code below:

   xcrun clang++ -std=c++11 -stdlib=libc++ test.cc

It outputs the ‘create’ line, but never any ‘destroy’.

If I don’t call dispatch_source_set_event_handler then I see the expected ‘destroy’. Alternatively I can call an extra Block_release(), which also results in the shared pointer being destroyed.

This is on Mac OS X 10.8.2 Build 12C60 using Apple LLVM version 4.2 (clang-425.0.24) (based on LLVM 3.2svn).

----------8<----------

#include <dispatch/dispatch.h>
#include <Block.h>
#include <stdio.h>
#include <memory>

void setup_dispatch_source ()
{
   struct record_t
   {
      record_t ()  { fprintf(stderr, "%p: create\n", this); }
      ~record_t () { fprintf(stderr, "%p: destroy\n", this); }
   };

   std::shared_ptr<record_t> record(new record_t);
   auto block = Block_copy(^(){ fprintf(stderr, "%p\n", record.get()); });

   dispatch_source_t source = dispatch_source_create(DISPATCH_SOURCE_TYPE_VNODE, open("/tmp", O_EVTONLY, 0), DISPATCH_VNODE_REVOKE, dispatch_get_main_queue());
   dispatch_source_set_event_handler(source, block);
   dispatch_source_set_event_handler_f(source, NULL);

   Block_release(block);
}

int main (int argc, char const* argv[])
{
   setup_dispatch_source();
   return 0;
}