CFAllocatorSetDefault seems to work on a per-thread basis. E.g.:


$ cat p.mm
//===============================
#import <Foundation/Foundation.h>
#include <pthread.h>

void do_bad_stuff() {
  NSURL *base = [[NSURL alloc] initWithString:@"file://localhost/Users/glider/Library/"];
  NSURL *u = [[NSURL alloc] initWithString:@"Saved Application State" relativeToURL:base];
}

void *worker(void *_) {
#ifndef REPLACE_IN_MAIN_THREAD
  CFAllocatorSetDefault(kCFAllocatorMallocZone);
#endif
  do_bad_stuff();
  return NULL;
}

int main() {
#ifdef REPLACE_IN_MAIN_THREAD
  CFAllocatorSetDefault(kCFAllocatorMallocZone);
#endif
  pthread_t th;
  pthread_create(&th, NULL, worker, NULL);
  pthread_join(th, NULL);
  return 0;
}
//===============================
$ clang++ p.mm -o p -framework Foundation -DREPLACE_IN_MAIN_THREAD && ./p   # Everything
fine
$ clang++ p.mm -o p -framework Foundation -UREPLACE_IN_MAIN_THREAD && ./p
p(54794,0x107281000) malloc: *** error for object 0x7ff7c8e002f8: pointer being freed
was not allocated
*** set a breakpoint in malloc_error_break to debug
Abort trap: 6

(this is an example from issue 70, which may stop working under ASan at once)

We need to reset the default CF allocator upon each thread creation.