[Basic] Avoid reentrant stat collection (swiftlang#29407)

[Basic] Avoid reentrant stat collection

Author: hamishknight

include/swift/Basic/Statistic.h

@@ -162,6 +162,10 @@ class UnifiedStatsReporter {
   std::unique_ptr<StatsProfilers> EventProfilers;
   std::unique_ptr<StatsProfilers> EntityProfilers;
 
+  /// Whether we are currently flushing statistics and should not therefore
+  /// record any additional stats until we've finished.
+  bool IsFlushingTracesAndProfiles;
+
   void publishAlwaysOnStatsToLLVM();
   void printAlwaysOnStatsAndTimers(raw_ostream &OS);
 

lib/Basic/Statistic.cpp

@@ -25,6 +25,7 @@
 #include "llvm/Support/Path.h"
 #include "llvm/Support/Process.h"
 #include "llvm/Support/raw_ostream.h"
+#include "llvm/Support/SaveAndRestore.h"
 #include <chrono>
 #include <limits>
 
@@ -348,7 +349,8 @@ UnifiedStatsReporter::UnifiedStatsReporter(StringRef ProgramName,
                                         ProgramName, "Running Program")),
     SourceMgr(SM),
     ClangSourceMgr(CSM),
-    RecursiveTimers(llvm::make_unique<RecursionSafeTimers>())
+    RecursiveTimers(llvm::make_unique<RecursionSafeTimers>()),
+    IsFlushingTracesAndProfiles(false)
 {
   path::append(StatsFilename, makeStatsFileName(ProgramName, AuxName));
   path::append(TraceFilename, makeTraceFileName(ProgramName, AuxName));
@@ -557,6 +559,13 @@ UnifiedStatsReporter::saveAnyFrontendStatsEvents(
     bool IsEntry)
 {
   assert(MainThreadID == std::this_thread::get_id());
+
+  // Don't record any new stats if we're currently flushing the ones we've
+  // already recorded. This can happen when requests get kicked off when
+  // computing source ranges.
+  if (IsFlushingTracesAndProfiles)
+    return;
+
   // First make a note in the recursion-safe timers; these
   // are active anytime UnifiedStatsReporter is active.
   if (IsEntry) {
@@ -711,6 +720,10 @@ UnifiedStatsReporter::~UnifiedStatsReporter()
 
 void
 UnifiedStatsReporter::flushTracesAndProfiles() {
+  // Note that we're currently flushing statistics and shouldn't record any
+  // more until we've finished.
+  llvm::SaveAndRestore<bool> flushing(IsFlushingTracesAndProfiles, true);
+
   if (FrontendStatsEvents && SourceMgr) {
     std::error_code EC;
     raw_fd_ostream tstream(TraceFilename, EC, fs::F_Append | fs::F_Text);