Index: compiler-rt/trunk/lib/lsan/lsan_common_mac.cc
===================================================================
--- compiler-rt/trunk/lib/lsan/lsan_common_mac.cc
+++ compiler-rt/trunk/lib/lsan/lsan_common_mac.cc
@@ -146,7 +146,7 @@
 }
 
 void DoStopTheWorld(StopTheWorldCallback callback, void *argument) {
-  CHECK(0 && "unimplemented");
+  StopTheWorld(callback, argument);
 }
 
 } // namespace __lsan
Index: compiler-rt/trunk/lib/sanitizer_common/sanitizer_stoptheworld_mac.cc
===================================================================
--- compiler-rt/trunk/lib/sanitizer_common/sanitizer_stoptheworld_mac.cc
+++ compiler-rt/trunk/lib/sanitizer_common/sanitizer_stoptheworld_mac.cc
@@ -17,6 +17,8 @@
                       defined(__i386))
 
 #include <mach/mach.h>
+#include <mach/thread_info.h>
+#include <pthread.h>
 
 #include "sanitizer_stoptheworld.h"
 
@@ -44,8 +46,51 @@
   InternalMmapVector<SuspendedThreadInfo> threads_;
 };
 
+struct RunThreadArgs {
+  StopTheWorldCallback callback;
+  void *argument;
+};
+
+void RunThread(void *arg) {
+  struct RunThreadArgs *run_args = (struct RunThreadArgs *)arg;
+  SuspendedThreadsListMac suspended_threads_list;
+
+  mach_port_t task;
+  kern_return_t err = task_for_pid(mach_task_self(), internal_getpid(), &task);
+  if (err != KERN_SUCCESS) {
+    VReport(1, "Getting task from pid failed (errno %d).\n", err);
+    return;
+  }
+
+  thread_array_t threads;
+  mach_msg_type_number_t num_threads;
+
+  err = task_threads(task, &threads, &num_threads);
+  if (err != KERN_SUCCESS) {
+    VReport(1, "Failed to get threads for task (errno %d).\n", err);
+    return;
+  }
+
+  thread_t thread_self = mach_thread_self();
+  for (unsigned int i = 0; i < num_threads; ++i) {
+    if (threads[i] == thread_self) continue;
+
+    thread_suspend(threads[i]);
+    suspended_threads_list.Append(threads[i]);
+  }
+
+  run_args->callback(suspended_threads_list, run_args->argument);
+
+  uptr num_suspended = suspended_threads_list.ThreadCount();
+  for (unsigned int i = 0; i < num_suspended; ++i) {
+    thread_resume(suspended_threads_list.GetThread(i));
+  }
+}
+
 void StopTheWorld(StopTheWorldCallback callback, void *argument) {
-  CHECK(0 && "unimplemented");
+  struct RunThreadArgs arg = {callback, argument};
+  pthread_t run_thread = (pthread_t)internal_start_thread(RunThread, &arg);
+  internal_join_thread(run_thread);
 }
 
 #if defined(__x86_64__)