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Add lock to SpanContext to protect baggage #83

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Apr 18, 2018
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Add lock to SpanContext to protect baggage #83

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17 changes: 16 additions & 1 deletion src/jaegertracing/SpanContext.h
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Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,7 @@

#include <iomanip>
#include <iostream>
#include <mutex>
#include <string>
#include <unordered_map>

Expand All @@ -41,6 +42,7 @@ class SpanContext : public opentracing::SpanContext {
, _spanID(0)
, _parentID(0)
, _flags(0)
, _mutex()
{
}

Expand All @@ -56,6 +58,7 @@ class SpanContext : public opentracing::SpanContext {
, _flags(flags)
, _baggage(baggage)
, _debugID(debugID)
, _mutex()
{
}

Expand Down Expand Up @@ -98,13 +101,15 @@ class SpanContext : public opentracing::SpanContext {

SpanContext withBaggage(const StrMap& baggage) const
{
std::lock_guard<std::mutex> lock(_mutex);
return SpanContext(
_traceID, _spanID, _parentID, _flags, baggage, _debugID);
}

template <typename Function>
void forEachBaggageItem(Function f) const
{
std::lock_guard<std::mutex> lock(_mutex);
for (auto&& pair : _baggage) {
if (!f(pair.first, pair.second)) {
break;
Expand All @@ -115,6 +120,7 @@ class SpanContext : public opentracing::SpanContext {
template <typename Function>
void forEachBaggageItem(Function f)
{
std::lock_guard<std::mutex> lock(_mutex);
for (auto&& pair : _baggage) {
if (!f(pair.first, pair.second)) {
break;
Expand Down Expand Up @@ -160,9 +166,17 @@ class SpanContext : public opentracing::SpanContext {

bool operator==(const SpanContext& rhs) const
{
{
std::lock(_mutex, rhs._mutex);
std::lock_guard<std::mutex> lock(_mutex, std::adopt_lock);
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can this deadlock? this grabs its own lock and rhs grabs its own lock and then we're stuck?

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I was hoping you wouldn't pay too much attention to this. std::lock is a cool trick in C++11 that locks two mutexes without causing deadlock (essentially a loop of try_lock under the hood):

Locks the given Lockable objects lock1, lock2, ..., lockn using a deadlock avoidance algorithm to avoid deadlock.
http://en.cppreference.com/w/cpp/thread/lock

The lock guard stuff is just to make sure we unlock, doesn't acquire the lock again. Serves same purpose as defer mutex.Unlock() would in Go.

std::lock_guard<std::mutex> rhsLock(rhs._mutex, std::adopt_lock);
if (_baggage != rhs._baggage) {
return false;
}
}
return _traceID == rhs._traceID && _spanID == rhs._spanID &&
_parentID == rhs._parentID && _flags == rhs._flags &&
_baggage == rhs._baggage && _debugID == rhs._debugID;
_debugID == rhs._debugID;
}

private:
Expand All @@ -172,6 +186,7 @@ class SpanContext : public opentracing::SpanContext {
unsigned char _flags;
StrMap _baggage;
std::string _debugID;
mutable std::mutex _mutex; // Protects _baggage.
};

} // namespace jaegertracing
Expand Down