r210225 - Flush C stdio streams upon process termination

[Zachary Turner]

Thanks, sorry about that.  Will keep it in mind next time when editing c
code.


On Fri, Jun 6, 2014 at 4:12 AM, Timur Iskhodzhanov <timurrrr at google.com>
wrote:

>
>
> 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
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>>
>
> 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.
>
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