1/* 2 * Copyright 2014 Google Inc. 3 * 4 * Use of this source code is governed by a BSD-style license that can be 5 * found in the LICENSE file. 6 */ 7 8#ifndef SkDynamicAnnotations_DEFINED 9#define SkDynamicAnnotations_DEFINED 10 11// This file contains macros used to send out-of-band signals to dynamic instrumentation systems, 12// namely thread sanitizer. This is a cut-down version of the full dynamic_annotations library with 13// only the features used by Skia. 14 15// We check the same define to know to enable the annotations, but prefix all our macros with SK_. 16#if DYNAMIC_ANNOTATIONS_ENABLED 17 18extern "C" { 19// TSAN provides these hooks. 20void AnnotateIgnoreReadsBegin(const char* file, int line); 21void AnnotateIgnoreReadsEnd(const char* file, int line); 22} // extern "C" 23 24// SK_ANNOTATE_UNPROTECTED_READ can wrap any variable read to tell TSAN to ignore that it appears to 25// be a racy read. This should be used only when we can make an external guarantee that though this 26// particular read is racy, it is being used as part of a mechanism which is thread safe. Examples: 27// - the first check in double-checked locking; 28// - checking if a ref count is equal to 1. 29// Note that in both these cases, we must still add terrifyingly subtle memory barriers to provide 30// that overall thread safety guarantee. Using this macro to shut TSAN up without providing such an 31// external guarantee is pretty much never correct. 32template <typename T> 33inline T SK_ANNOTATE_UNPROTECTED_READ(const volatile T& x) { 34 AnnotateIgnoreReadsBegin(__FILE__, __LINE__); 35 T read = x; 36 AnnotateIgnoreReadsEnd(__FILE__, __LINE__); 37 return read; 38} 39 40#else // !DYNAMIC_ANNOTATIONS_ENABLED 41 42#define SK_ANNOTATE_UNPROTECTED_READ(x) (x) 43 44#endif 45 46#endif//SkDynamicAnnotations_DEFINED 47