[NFC][TSan][libdispatch] Fix test for dispatch_apply[_f]

[yln]

Summary

• Array index out of bounds: 100 iterations, but size of array is 2.
• Unmatched barrier_init (2) with barrier_wait (200)
• Number of iterations must be smaller than the available parallelism for the queue, otherwise we deadlock (since every barrier_wait call blocks the thread).

Scary: All of this worked reliably in gcd-apply.mm (for Darwin)

[kubamracek]

Make size just "2" to make sure we're actually able to satisfy the barrier on low-end machines. Other that that, LGTM.

compiler-rt/trunk/test/tsan/libdispatch/apply.c

 // RUN: %clang_tsan %s -o %t
-// RUN: %run %t 2>&1 | FileCheck %s
-
-// TODO(yln): Deadlocks while gcd-apply.mm does not. What's the difference
-//            between C and Obj-C compiler?
-// REQUIRES: disable
+// RUN: %run %t 2>&1 | FileCheck %s --implicit-check-not='ThreadSanitizer'
 
 #include <dispatch/dispatch.h>
 
 #include "../test.h"
 
+const size_t size = 2;
 long global;
-long array[2];
+long array[size];
 
 void callback(void *context, size_t i) {
   long n = global;
   array[i] = n + i;
   barrier_wait(&barrier);
 }
 
 int main(int argc, const char *argv[]) {
-  barrier_init(&barrier, 2);
   fprintf(stderr, "start\n");
 
   // Warm up GCD (workaround for macOS Sierra where dispatch_apply might run single-threaded).
   dispatch_sync(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{ });
 
   dispatch_queue_t q = dispatch_queue_create("my.queue", DISPATCH_QUEUE_CONCURRENT);
 
   global = 42;
 
-  dispatch_apply(100, q, ^(size_t i) {
+  barrier_init(&barrier, size);
+  dispatch_apply(size, q, ^(size_t i) {
     long n = global;
     array[i] = n + i;
     barrier_wait(&barrier);
   });
 
-  for (int i = 0; i < 100; i++) {
-    fprintf(stderr, "array[%d] = %ld\n", i, array[i]);
+  for (size_t i = 0; i < size; i++) {
+    fprintf(stderr, "array[%ld] = %ld\n", i, array[i]);
   }
 
-  global = 43;
+  global = 142;
+
+  barrier_init(&barrier, size);
+  dispatch_apply_f(size, q, NULL, &callback);
 
-  dispatch_apply_f(100, q, NULL, &callback);
+  for (size_t i = 0; i < size; i++) {
+    fprintf(stderr, "array[%ld] = %ld\n", i, array[i]);
+  }
 
   fprintf(stderr, "done\n");
   return 0;
 }
 
 // CHECK: start
+// CHECK: array[0] = 42
+// CHECK: array[1] = 43
+// CHECK: array[0] = 142
+// CHECK: array[1] = 143
 // CHECK: done
 // CHECK-NOT: WARNING: ThreadSanitizer