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