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// Copyright 2017 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
#ifndef StackUtil_h
#define StackUtil_h
#include "wtf/Compiler.h"
#include "wtf/WTFExport.h"
#include "wtf/build_config.h"
#include <stddef.h>
#include <stdint.h>
namespace WTF {
WTF_EXPORT size_t getUnderestimatedStackSize();
WTF_EXPORT void* getStackStart();
namespace internal {
WTF_EXPORT uintptr_t mainThreadUnderestimatedStackSize();
#if OS(WIN) && COMPILER(MSVC)
size_t threadStackSize();
#endif
// Returns true if the function is not called on the main thread. Note carefully
// that this function may have false positives, i.e. it can return true even if
// we are on the main thread. If the function returns false, we are certainly
// not on the main thread. Must be WTF_EXPORT due to template inlining in
// ThreadSpecific.
inline WTF_EXPORT bool mayNotBeMainThread() {
// getStackStart is exclusive, not inclusive (i.e. it points past the last
// page of the stack in linear order). So, to ensure an inclusive comparison,
// subtract here and in mainThreadUnderestimatedStackSize().
static uintptr_t s_mainThreadStackStart =
reinterpret_cast<uintptr_t>(getStackStart()) - sizeof(void*);
static uintptr_t s_mainThreadUnderestimatedStackSize =
mainThreadUnderestimatedStackSize();
uintptr_t dummy;
uintptr_t addressDiff =
s_mainThreadStackStart - reinterpret_cast<uintptr_t>(&dummy);
// This is a fast way to judge if we are in the main thread.
// If |&dummy| is within |s_mainThreadUnderestimatedStackSize| byte from
// the stack start of the main thread, we judge that we are in
// the main thread.
return addressDiff >= s_mainThreadUnderestimatedStackSize;
}
} // namespace internal
} // namespace WTF
#endif // StackUtil_h
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