r210225 - Flush C stdio streams upon process termination

[Timur Iskhodzhanov]

2014-06-05 4:13 GMT+04:00 Reid Kleckner <reid at kleckner.net>:

> Author: rnk
> Date: Wed Jun  4 19:13:43 2014
> New Revision: 210225
>
> URL: http://llvm.org/viewvc/llvm-project?rev=210225&view=rev
> Log:
> Flush C stdio streams upon process termination
>
> 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.
>
> Test Plan:
> Without patch: Ran check-clang 10 times and saw over 30 Unexpected
> failures on every run.
> With patch: Ran check-clang 10 times and saw 0 unexpected failures across
> all runs.
>
> Reviewers: rnk
>
> Differential Revision: http://reviews.llvm.org/D4021
>
> Patch by Zachary Turner!
>
> Modified:
>     cfe/trunk/tools/c-arcmt-test/c-arcmt-test.c
>     cfe/trunk/tools/c-index-test/c-index-test.c
>
> Modified: cfe/trunk/tools/c-arcmt-test/c-arcmt-test.c
> URL:
> http://llvm.org/viewvc/llvm-project/cfe/trunk/tools/c-arcmt-test/c-arcmt-test.c?rev=210225&r1=210224&r2=210225&view=diff
>
> ==============================================================================
> --- cfe/trunk/tools/c-arcmt-test/c-arcmt-test.c (original)
> +++ cfe/trunk/tools/c-arcmt-test/c-arcmt-test.c Wed Jun  4 19:13:43 2014
> @@ -97,14 +97,20 @@ typedef struct thread_info {
>  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");
>
> Modified: cfe/trunk/tools/c-index-test/c-index-test.c
> URL:
> http://llvm.org/viewvc/llvm-project/cfe/trunk/tools/c-index-test/c-index-test.c?rev=210225&r1=210224&r2=210225&view=diff
>
> ==============================================================================
> --- cfe/trunk/tools/c-index-test/c-index-test.c (original)
> +++ cfe/trunk/tools/c-index-test/c-index-test.c Wed Jun  4 19:13:43 2014
> @@ -4116,14 +4116,20 @@ typedef struct thread_info {
>  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
>
>
> _______________________________________________
> cfe-commits mailing list
> cfe-commits at cs.uiuc.edu
> http://lists.cs.uiuc.edu/mailman/listinfo/cfe-commits
>

FYI
tools/clang/tools/c-index-test/c-index-test.c:4122:3: warning: C++ style
comments are not allowed in ISO C90 [enabled by default]
   // stdout, and surprisingly even stderr, are not always flushed on
process
   ^

Fixed in r210325.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/cfe-commits/attachments/20140606/8c47aa94/attachment.html>