Properly lock access to static variables.
There were a few race conditions where the static method would test the validity of the hitograms_ static variable before attempting to use the lock_ to protect access to it but nothing then prevented the destructor to free both the lock_ and the hitograms_ memory.
So I decided to not use a dynamic allocation of the static lock_ to resolve this problem.
BUG=38354
TEST=Hard to repro exit scenario crashes.
Review URL: http://codereview.chromium.org/5784005
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@70054 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/base/metrics/histogram.cc b/base/metrics/histogram.cc
index d87640fa6d..75df12e 100644
--- a/base/metrics/histogram.cc
+++ b/base/metrics/histogram.cc
@@ -904,12 +904,21 @@
// provide support for all future calls.
StatisticsRecorder::StatisticsRecorder() {
DCHECK(!histograms_);
- lock_ = new Lock;
+ if (lock_ == NULL) {
+ // This will leak on purpose. It's the only way to make sure we won't race
+ // against the static uninitialization of the module while one of our
+ // static methods relying on the lock get called at an inappropriate time
+ // during the termination phase. Since it's a static data member, we will
+ // leak one per process, which would be similar to the instance allocated
+ // during static initialization and released only on process termination.
+ lock_ = new Lock;
+ }
+ AutoLock auto_lock(*lock_);
histograms_ = new HistogramMap;
}
StatisticsRecorder::~StatisticsRecorder() {
- DCHECK(histograms_);
+ DCHECK(histograms_ && lock_);
if (dump_on_exit_) {
std::string output;
@@ -917,14 +926,22 @@
LOG(INFO) << output;
}
// Clean up.
- delete histograms_;
- histograms_ = NULL;
- delete lock_;
- lock_ = NULL;
+ HistogramMap* histograms = NULL;
+ {
+ AutoLock auto_lock(*lock_);
+ histograms = histograms_;
+ histograms_ = NULL;
+ }
+ delete histograms;
+ // We don't delete lock_ on purpose to avoid having to properly protect
+ // against it going away after we checked for NULL in the static methods.
}
// static
-bool StatisticsRecorder::WasStarted() {
+bool StatisticsRecorder::IsActive() {
+ if (lock_ == NULL)
+ return false;
+ AutoLock auto_lock(*lock_);
return NULL != histograms_;
}
@@ -935,10 +952,12 @@
// destroyed before assignment (when value was returned by new).
// static
void StatisticsRecorder::Register(Histogram* histogram) {
+ if (lock_ == NULL)
+ return;
+ AutoLock auto_lock(*lock_);
if (!histograms_)
return;
const std::string name = histogram->histogram_name();
- AutoLock auto_lock(*lock_);
// Avoid overwriting a previous registration.
if (histograms_->end() == histograms_->find(name))
(*histograms_)[name] = histogram;
@@ -947,7 +966,7 @@
// static
void StatisticsRecorder::WriteHTMLGraph(const std::string& query,
std::string* output) {
- if (!histograms_)
+ if (!IsActive())
return;
output->append("<html><head><title>About Histograms");
if (!query.empty())
@@ -971,7 +990,7 @@
// static
void StatisticsRecorder::WriteGraph(const std::string& query,
std::string* output) {
- if (!histograms_)
+ if (!IsActive())
return;
if (query.length())
StringAppendF(output, "Collections of histograms for %s\n", query.c_str());
@@ -990,9 +1009,11 @@
// static
void StatisticsRecorder::GetHistograms(Histograms* output) {
- if (!histograms_)
+ if (lock_ == NULL)
return;
AutoLock auto_lock(*lock_);
+ if (!histograms_)
+ return;
for (HistogramMap::iterator it = histograms_->begin();
histograms_->end() != it;
++it) {
@@ -1003,9 +1024,11 @@
bool StatisticsRecorder::FindHistogram(const std::string& name,
scoped_refptr<Histogram>* histogram) {
- if (!histograms_)
+ if (lock_ == NULL)
return false;
AutoLock auto_lock(*lock_);
+ if (!histograms_)
+ return false;
HistogramMap::iterator it = histograms_->find(name);
if (histograms_->end() == it)
return false;
@@ -1016,7 +1039,11 @@
// private static
void StatisticsRecorder::GetSnapshot(const std::string& query,
Histograms* snapshot) {
+ if (lock_ == NULL)
+ return;
AutoLock auto_lock(*lock_);
+ if (!histograms_)
+ return;
for (HistogramMap::iterator it = histograms_->begin();
histograms_->end() != it;
++it) {
