tsan: add a test for flushing memory

[dvyukov]

Summary

Add a test for __tsan_flush_memory() and for background
flushing of the runtime memory.

compiler-rt/include/sanitizer/tsan_interface.h

 void __tsan_on_initialize();
 
 // User-provided callback invoked on TSan shutdown.
 // `failed` - Nonzero if TSan did detect issues, zero otherwise.
 // Return `0` if TSan should exit as if no issues were detected.  Return nonzero
 // if TSan should exit as if issues were detected.
 int __tsan_on_finalize(int failed);
 
+// Release TSan internal memory in a best-effort manner.
+void __tsan_flush_memory();
+
 #ifdef __cplusplus
 }  // extern "C"
 #endif
 
 #endif  // SANITIZER_TSAN_INTERFACE_H

compiler-rt/test/tsan/flush_memory.cpp

+// RUN: %clangxx_tsan -O1 %s -o %t && %env_tsan_opts="flush_memory_ms=1 flush_symbolizer_ms=1 memory_limit_mb=1" %deflake %t | FileCheck %s
+#include "test.h"
+
+long X, Y;
+
+void *Thread(void *arg) {
+  __atomic_fetch_add(&X, 1, __ATOMIC_SEQ_CST);
+  barrier_wait(&barrier);
+  barrier_wait(&barrier);
+  Y = 1;
+  return &Y;
+}
+
+int main() {
+  __tsan_flush_memory();
+  barrier_init(&barrier, 2);
+  __atomic_fetch_add(&X, 1, __ATOMIC_SEQ_CST);
+  pthread_t t;
+  pthread_create(&t, NULL, Thread, NULL);
+  barrier_wait(&barrier);
+  __tsan_flush_memory();
+  // Trigger a race to test flushing of the symbolizer cache.
+  Y = 2;
+  barrier_wait(&barrier);
+  pthread_join(t, NULL);
+  __atomic_fetch_add(&X, 1, __ATOMIC_SEQ_CST);
+  // Background runtime thread should do some flushes meanwhile.
+  sleep(2);
+  __tsan_flush_memory();
+  fprintf(stderr, "DONE\n");
+  return 0;
+}
+
+// CHECK: WARNING: ThreadSanitizer: data race
+// CHECK: DONE