[PATCH] Flush output streams upon process termination

[Zachary Turner]

Hi rnk,

Due to what can only be described as a CRT bug, stdout and amazingly even stderr are not always flushed upon process termination, especially when the system is under high threading pressure.  I have found two repros for this:

1) In lib\Support\Threading.cpp, change sys::Mutex to an std::recursive_mutex and run check-clang.  Usually between 30 and 40 tests will fail.
2) Add OutputDebugStrings in code that runs during static initialization and static shutdown.  This will sometimes generate similar failures.

After a substantial amount of troubleshooting and debugging, I found that I could reproduce this from the command line without running check-clang.  Simply make the mutex change described in #1, then manually run the following command many times by running it once, then pressing Up -> Enter very quickly:

D:\src\llvm\build\vs2013\Debug\bin\c-index-test.EXE -cursor-at=D:\src\llvm\tools\clang\test\Index\targeted-preamble.h:2:15 D:\src\llvm\tools\clang\test\Index\targeted-cursor.c -include D:\src\llvm\build\vs2013\tools\clang\test\Index\Output\targeted-cursor.c.tmp.h -Xclang
-error-on-deserialized-decl=NestedVar1      -Xclang -error-on-deserialized-decl=TopVar    | D:\src\llvm\build\vs2013\Debug\bin\FileCheck.EXE D:\src\llvm\tools\clang\test\Index\targeted-cursor.c -check-prefix=PREAMBLE-CURSOR1

Sporadically they will fail, and attaching a debugger to a failed instance indicates that stdin of FileCheck.exe is empty.

Note that due to the repro in #2, we can rule out a bug in the STL's mutex implementation, and instead conclude that this is a real flake in the windows test harness.

http://reviews.llvm.org/D4021

Files:
  tools/c-arcmt-test/c-arcmt-test.c
  tools/c-index-test/c-index-test.c

Index: tools/c-arcmt-test/c-arcmt-test.c
===================================================================
--- tools/c-arcmt-test/c-arcmt-test.c
+++ tools/c-arcmt-test/c-arcmt-test.c
@@ -97,14 +97,20 @@
 void thread_runner(void *client_data_v) {
   thread_info *client_data = client_data_v;
   client_data->result = carcmttest_main(client_data->argc, client_data->argv);
-#ifdef __CYGWIN__
-  fflush(stdout);  /* stdout is not flushed on Cygwin. */
-#endif
+}
+
+static void flush_atexit(void) {
+  // stdout, and surprisingly even stderr, are not always flushed on process
+  // and thread exit, particularly when the system is under heavy load.
+  fflush(stdout);
+  fflush(stderr);
 }
 
 int main(int argc, const char **argv) {
   thread_info client_data;
 
+  atexit(flush_atexit);
+
 #if defined(_WIN32)
   if (getenv("LIBCLANG_LOGGING") == NULL)
     putenv("LIBCLANG_LOGGING=1");
Index: tools/c-index-test/c-index-test.c
===================================================================
--- tools/c-index-test/c-index-test.c
+++ tools/c-index-test/c-index-test.c
@@ -4116,14 +4116,20 @@
 void thread_runner(void *client_data_v) {
   thread_info *client_data = client_data_v;
   client_data->result = cindextest_main(client_data->argc, client_data->argv);
-#ifdef __CYGWIN__
-  fflush(stdout);  /* stdout is not flushed on Cygwin. */
-#endif
+}
+
+static void flush_atexit(void) {
+  // stdout, and surprisingly even stderr, are not always flushed on process
+  // and thread exit, particularly when the system is under heavy load.
+  fflush(stdout);
+  fflush(stderr);
 }
 
 int main(int argc, const char **argv) {
   thread_info client_data;
 
+  atexit(flush_atexit);
+
 #ifdef CLANG_HAVE_LIBXML
   LIBXML_TEST_VERSION
 #endif
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