blob: 6d21cddb940b363d16a614d3b9f54f59af3e7dcf [file] [log] [blame]
* Copyright 2014 Google Inc.
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
#ifndef SkDynamicAnnotations_DEFINED
#define SkDynamicAnnotations_DEFINED
// This file contains macros used to send out-of-band signals to dynamic instrumentation systems,
// namely thread sanitizer. This is a cut-down version of the full dynamic_annotations library with
// only the features used by Skia.
// We check the same define to know to enable the annotations, but prefix all our macros with SK_.
extern "C" {
// TSAN provides these hooks.
void AnnotateIgnoreReadsBegin(const char* file, int line);
void AnnotateIgnoreReadsEnd(const char* file, int line);
} // extern "C"
// SK_ANNOTATE_UNPROTECTED_READ can wrap any variable read to tell TSAN to ignore that it appears to
// be a racy read. This should be used only when we can make an external guarantee that though this
// particular read is racy, it is being used as part of a mechanism which is thread safe. Examples:
// - the first check in double-checked locking;
// - checking if a ref count is equal to 1.
// Note that in both these cases, we must still add terrifyingly subtle memory barriers to provide
// that overall thread safety guarantee. Using this macro to shut TSAN up without providing such an
// external guarantee is pretty much never correct.
template <typename T>
inline T SK_ANNOTATE_UNPROTECTED_READ(const volatile T& x) {
AnnotateIgnoreReadsBegin(__FILE__, __LINE__);
T read = x;
AnnotateIgnoreReadsEnd(__FILE__, __LINE__);
return read;