[libFuzzer] handle SIGUSR1/SIGUSR2 and try to exit grafully on these signals

git-svn-id: https://llvm.org/svn/llvm-project/compiler-rt/trunk/lib/fuzzer@317829 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/FuzzerLoop.cpp b/FuzzerLoop.cpp
index f4771e1..97bc1c6 100644
--- a/FuzzerLoop.cpp
+++ b/FuzzerLoop.cpp
@@ -216,6 +216,12 @@
   F->InterruptCallback();
 }
 
+void Fuzzer::StaticGracefulExitCallback() {
+  assert(F);
+  F->GracefulExitRequested = true;
+  Printf("INFO: signal received, trying to exit gracefully\n");
+}
+
 void Fuzzer::StaticFileSizeExceedCallback() {
   Printf("==%lu== ERROR: libFuzzer: file size exceeded\n", GetPid());
   exit(1);
@@ -246,6 +252,13 @@
   _Exit(Options.ErrorExitCode);
 }
 
+void Fuzzer::MaybeExitGracefully() {
+  if (!GracefulExitRequested) return;
+  Printf("==%lu== INFO: libFuzzer: exiting as requested\n", GetPid());
+  PrintFinalStats();
+  _Exit(0);
+}
+
 void Fuzzer::InterruptCallback() {
   Printf("==%lu== libFuzzer: run interrupted; exiting\n", GetPid());
   PrintFinalStats();
@@ -621,6 +634,7 @@
   for (int i = 0; i < Options.MutateDepth; i++) {
     if (TotalNumberOfRuns >= Options.MaxNumberOfRuns)
       break;
+    MaybeExitGracefully();
     size_t NewSize = 0;
     NewSize = MD.Mutate(CurrentUnitData, Size, CurrentMaxMutationLen);
     assert(NewSize > 0 && "Mutator returned empty unit");