[llvm] Protect signpost map with a mutex

[JDevlieghere]

Summary

Use a mutex to protect concurrent access to the signpost map.

This fixes nondeterministic crashes in LLDB that appeared after using signposts in the timer implementation.

[JDevlieghere]

ping

[dsanders]

A sys::SmartMutex equivalent of this would LGTM. Let me know if there's a reason we should stick to std::mutex

llvm/lib/Support/Signposts.cpp

42

Timer.cpp uses sys::SmartMutex so that single threaded builds don't have to do the mutex. We should do the same here unless there's a good reason to use std::mutex

[JDevlieghere]

Use SmartMutex and SmartScopedLock.

[JDevlieghere]

llvm/lib/Support/Signposts.cpp

42

Makes sense, thanks, I've updated the patch.

[dsanders]

LGTM

llvm/lib/Support/Signposts.cpp

 //===-- Signposts.cpp - Interval debug annotations ------------------------===//
 //
 //                     The LLVM Compiler Infrastructure
 //
 // This file is distributed under the University of Illinois Open Source
 // License. See LICENSE.TXT for details.
 //
 //===----------------------------------------------------------------------===//
 
 #include "llvm/Support/Signposts.h"
 #include "llvm/Support/Timer.h"
 
 #include "llvm/Config/config.h"
 #if LLVM_SUPPORT_XCODE_SIGNPOSTS
 #include "llvm/ADT/DenseMap.h"
+#include "llvm/Support/Mutex.h"
 #include <os/signpost.h>
 #endif // if LLVM_SUPPORT_XCODE_SIGNPOSTS
 
 using namespace llvm;
 
 #if LLVM_SUPPORT_XCODE_SIGNPOSTS
 namespace {
 os_log_t *LogCreator() {

 
 namespace llvm {
 class SignpostEmitterImpl {
   using LogPtrTy = std::unique_ptr<os_log_t, std::function<void(os_log_t *)>>;
   using LogTy = LogPtrTy::element_type;
 
   LogPtrTy SignpostLog;
   DenseMap<const void *, os_signpost_id_t> Signposts;
+  sys::SmartMutex<true> Mutex;
 
   LogTy &getLogger() const { return *SignpostLog; }
   os_signpost_id_t getSignpostForObject(const void *O) {
+    sys::SmartScopedLock<true> Lock(Mutex);
     const auto &I = Signposts.find(O);
     if (I != Signposts.end())
       return I->second;
 
     const auto &Inserted = Signposts.insert(
         std::make_pair(O, os_signpost_id_make_with_pointer(getLogger(), O)));
     return Inserted.first->second;
   }