Support: add llvm::unique_lock

Based on the STL class of the same name, it guards a mutex
while also allowing it to be unlocked conditionally before
destruction.

This eliminates the last naked usages of mutexes in LLVM and
clang.

It also uncovered and fixed a bug in callExternalFunction()
when compiled without USE_LIBFFI, where the mutex would never
be unlocked if the end of the function was reached.

llvm-svn: 216338

1 files changed, 17 insertions, 16 deletions

diff --git a/llvm/lib/Support/Unix/Signals.inc b/llvm/lib/Support/Unix/Signals.inc
index 34c39c9ad92..c820553665d 100644
--- a/llvm/lib/Support/Unix/Signals.inc
+++ b/llvm/lib/Support/Unix/Signals.inc
@@ -15,6 +15,7 @@
 #include "Unix.h"
 #include "llvm/ADT/STLExtras.h"
 #include "llvm/Support/Mutex.h"
+#include "llvm/Support/UniqueLock.h"
 #include <algorithm>
 #include <string>
 #include <vector>
@@ -162,25 +163,25 @@ static RETSIGTYPE SignalHandler(int Sig) {
   sigfillset(&SigMask);
   sigprocmask(SIG_UNBLOCK, &SigMask, nullptr);
 
-  SignalsMutex.lock();
-  RemoveFilesToRemove();
-
-  if (std::find(IntSigs, IntSigsEnd, Sig) != IntSigsEnd) {
-    if (InterruptFunction) {
-      void (*IF)() = InterruptFunction;
-      SignalsMutex.unlock();
-      InterruptFunction = nullptr;
-      IF();        // run the interrupt function.
+  {
+    unique_lock<SmartMutex<true>> Guard(SignalsMutex);
+    RemoveFilesToRemove();
+
+    if (std::find(IntSigs, IntSigsEnd, Sig) != IntSigsEnd) {
+      if (InterruptFunction) {
+        void (*IF)() = InterruptFunction;
+        Guard.unlock();
+        InterruptFunction = nullptr;
+        IF();        // run the interrupt function.
+        return;
+      }
+
+      Guard.unlock();
+      raise(Sig);   // Execute the default handler.
       return;
-    }
-
-    SignalsMutex.unlock();
-    raise(Sig);   // Execute the default handler.
-    return;
+   }
   }
 
-  SignalsMutex.unlock();
-
   // Otherwise if it is a fault (like SEGV) run any handler.
   for (unsigned i = 0, e = CallBacksToRun.size(); i != e; ++i)
     CallBacksToRun[i].first(CallBacksToRun[i].second);