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/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at */
#include "ThreadAnnotation.h"
#include <stddef.h>
#include "mozilla/Assertions.h"
#include "mozilla/StaticMutex.h"
#include "mozilla/UniquePtr.h"
#include "prthread.h"
#include "nsDebug.h"
#include "nsExceptionHandler.h"
#include "nsString.h"
#include "nsTArray.h"
using mozilla::StaticMutex;
using mozilla::StaticMutexAutoLock;
using mozilla::UniquePtr;
namespace CrashReporter {
namespace {
#ifdef XP_MACOSX
* On the Mac, exception handler callbacks are invoked in a context where all
* other threads are paused. As a result, attempting to acquire a mutex is
* problematic because 1) the mutex may be held by another thread which is
* now suspended and 2) acquiring an unheld mutex can trigger memory allocation
* which generally requires allocator locks. This class is a wrapper around a
* StaticMutex, providing an IsLocked() method which only makes sense to use
* in the Mac exception handling context when other threads are paused.
class MacCrashReporterLock {
void Lock() {
sIsLocked = true;
void Unlock() {
sIsLocked = false;
* Returns true if the lock is held at the time the method is called.
* The return value is out-of-date by the time this method returns unless
* we have a guarantee that other threads are not running such as in Mac
* breadkpad exception handler context.
bool IsLocked() { return sIsLocked; }
void AssertCurrentThreadOwns() { sInnerMutex.AssertCurrentThreadOwns(); }
static StaticMutex sInnerMutex;
static bool sIsLocked;
StaticMutex MacCrashReporterLock::sInnerMutex;
bool MacCrashReporterLock::sIsLocked;
// Use MacCrashReporterLock for locking
typedef mozilla::detail::BaseAutoLock<MacCrashReporterLock&>
typedef MacCrashReporterLock CrashReporterLockType;
#else /* !XP_MACOSX */
// Use StaticMutex for locking
typedef StaticMutexAutoLock CrashReporterAutoLock;
typedef StaticMutex CrashReporterLockType;
#endif /* XP_MACOSX */
// Protects access to sInitialized and sThreadAnnotations.
static CrashReporterLockType sMutex;
class ThreadAnnotationSpan {
ThreadAnnotationSpan(uint32_t aBegin, uint32_t aEnd)
: mBegin(aBegin), mEnd(aEnd) {
MOZ_ASSERT(mBegin < mEnd);
class Comparator {
bool Equals(const ThreadAnnotationSpan* const& a,
const ThreadAnnotationSpan* const& b) const {
return a->mBegin == b->mBegin;
bool LessThan(const ThreadAnnotationSpan* const& a,
const ThreadAnnotationSpan* const& b) const {
return a->mBegin < b->mBegin;
// ~ThreadAnnotationSpan() does nontrivial thing. Make sure we don't
// instantiate accidentally.
ThreadAnnotationSpan(const ThreadAnnotationSpan& aOther) = delete;
ThreadAnnotationSpan& operator=(const ThreadAnnotationSpan& aOther) = delete;
friend class ThreadAnnotationData;
friend class Comparator;
uint32_t mBegin;
uint32_t mEnd;
// This class keeps the flat version of thread annotations for each thread.
// When a thread calls CrashReporter::SetCurrentThreadName(), it adds
// information about the calling thread (thread id and name) to this class.
// When crash happens, the crash reporter gets flat representation and add to
// the crash annotation file.
class ThreadAnnotationData {
ThreadAnnotationData() = default;
~ThreadAnnotationData() = default;
// Adds <pre> tid:"thread name",</pre> annotation to the current annotations.
// Returns an instance of ThreadAnnotationSpan for cleanup on thread
// termination.
ThreadAnnotationSpan* AddThreadAnnotation(ThreadId aTid,
const char* aThreadName) {
if (!aTid || !aThreadName) {
return nullptr;
uint32_t oldLength = mData.Length();
mData.AppendPrintf("%u:\"%s\",", aTid, aThreadName);
uint32_t newLength = mData.Length();
ThreadAnnotationSpan* rv = new ThreadAnnotationSpan(oldLength, newLength);
return rv;
// Called on thread termination. Removes the thread annotation, represented as
// ThreadAnnotationSpan, from the flat representation.
void EraseThreadAnnotation(const ThreadAnnotationSpan& aThreadInfo) {
uint32_t begin = aThreadInfo.mBegin;
uint32_t end = aThreadInfo.mEnd;
if (!(begin < end && end <= mData.Length())) {
uint32_t cutLength = end - begin;
mData.Cut(begin, cutLength);
// Adjust the ThreadAnnotationSpan affected by data shifting.
size_t index = mDataSpans.BinaryIndexOf(&aThreadInfo,
for (size_t i = index + 1; i < mDataSpans.Length(); i++) {
ThreadAnnotationSpan* elem = mDataSpans[i];
MOZ_ASSERT(elem->mBegin >= cutLength);
MOZ_ASSERT(elem->mEnd > cutLength);
elem->mBegin -= cutLength;
elem->mEnd -= cutLength;
// No loner tracking aThreadInfo.
// Gets the flat representation of thread annotations.
void GetData(const std::function<void(const char*)>& aCallback) {
// The flat representation of thread annotations.
nsCString mData;
// This array tracks the created ThreadAnnotationSpan instances so that we
// can make adjustments accordingly when we cut substrings from mData on
// thread exit.
nsTArray<ThreadAnnotationSpan*> mDataSpans;
static bool sInitialized = false;
static UniquePtr<ThreadAnnotationData> sThreadAnnotations;
static unsigned sTLSThreadInfoKey = (unsigned)-1;
void ThreadLocalDestructor(void* aUserData) {
CrashReporterAutoLock lock(sMutex);
ThreadAnnotationSpan* aThreadInfo =
delete aThreadInfo;
// This is called on thread termination.
ThreadAnnotationSpan::~ThreadAnnotationSpan() {
// Note that we can't lock the mutex here because this function may be called
// from SetCurrentThreadName().
if (sThreadAnnotations) {
} // Anonymous namespace.
void InitThreadAnnotation() {
CrashReporterAutoLock lock(sMutex);
if (sInitialized) {
PRStatus status =
PR_NewThreadPrivateIndex(&sTLSThreadInfoKey, &ThreadLocalDestructor);
if (status == PR_FAILURE) {
sInitialized = true;
sThreadAnnotations = mozilla::MakeUnique<ThreadAnnotationData>();
void SetCurrentThreadName(const char* aName) {
if (PR_GetThreadPrivate(sTLSThreadInfoKey)) {
// Explicitly set TLS value to null (and call the dtor function ) before
// acquiring sMutex to avoid reentrant deadlock.
PR_SetThreadPrivate(sTLSThreadInfoKey, nullptr);
CrashReporterAutoLock lock(sMutex);
if (!sInitialized) {
ThreadAnnotationSpan* threadInfo =
sThreadAnnotations->AddThreadAnnotation(CurrentThreadId(), aName);
// This may destroy the old insatnce.
PR_SetThreadPrivate(sTLSThreadInfoKey, threadInfo);
void GetFlatThreadAnnotation(const std::function<void(const char*)>& aCallback,
bool aIsHandlingException) {
bool lockNeeded = true;
#ifdef XP_MACOSX
if (aIsHandlingException) {
// Don't acquire the lock on Mac because we are
// executing in exception context where all other
// threads are paused. If the lock is held, skip
// thread annotations to avoid deadlock caused by
// waiting for a suspended thread. If the lock
// isn't held, acquiring it serves no purpose and
// can trigger memory allocations.
if (sMutex.IsLocked()) {
lockNeeded = false;
if (lockNeeded) {
if (sThreadAnnotations) {
} else {
// Maybe already shutdown: call aCallback with empty annotation data.
if (lockNeeded) {
void ShutdownThreadAnnotation() {
CrashReporterAutoLock lock(sMutex);
sInitialized = false;
} // namespace CrashReporter