MSVC crash with '-DMEMDEBUG_LOG_SYNC'

[gvanem]

Building libcurl with -DCURLDEBUG and -DMEMDEBUG_LOG_SYNC for me causes crash in lib/memdebug.c inside curl_memdebug():

    setvbuf(logfile, (char *)NULL, _IOLBF, 0);

I.e. Dr. Watson triggers a run-time check followed by a crash. But this seems to work as intended:

    setvbuf(logfile, (char *)NULL, _IONBF, 0);

Anybody who can confirm this?

This seems to be the same as this Stackoverflow issue. I'm using MSVC-2015 (cl 19.00.23506 for x86) on Win-10.

[dfandrich]

I'm guessing the issue has to do with the size 0 passed in when line buffering; does it work if you pass in 1024 for example? In any case, unbuffering this stream is just as good (if not actually a better) of a solution in this case.

[gvanem]

does it work if you pass in 1024 for example?

It does.

Not sure what you mean by unbuffering this stream, but trying with this:

--- a/memdebug.c 2016-05-01 22:05:17
+++ b/memdebug.c 2016-05-25 19:41:33
@@ -118,9 +118,18 @@
     else
       logfile = stderr;
 #ifdef MEMDEBUG_LOG_SYNC
-    /* Flush the log file after every line so the log isn't lost in a crash */
+    /* Flush the log file after every line so the log isn't lost in a crash.
+     * For Win32, the mode *must* be _IONBF. Otherwise Dr. Watson triggers a
+     * run-time check followed by a crash.
+     *   Refs: https://msdn.microsoft.com/en-us/library/86cebhfs.aspx
+     *         http://stackoverflow.com/questions/15972550/what-is-the-use-of-setvbuf-in-an-applicationexecutable
+     */
+#if defined(WIN32)
+    setvbuf(logfile, (char *)NULL, _IONBF, 0);
+#else
     setvbuf(logfile, (char *)NULL, _IOLBF, 0);
 #endif
+#endif
   }
 }

seems okay.

[dfandrich]

I was talking about using _IONBF unconditionally, which sets the stream unbuffered. Don't bother making it conditional, just use _IONBF unconditionally, either the way you have it or the slightly simpler setbuf(logfile, (char*)NULL);

[gvanem]

Ah, yes this works:

--- a/memdebug.c 2016-05-01 22:05:17
+++ b(memdebug.c 2016-05-25 23:10:57
@@ -119,7 +119,7 @@
       logfile = stderr;
 #ifdef MEMDEBUG_LOG_SYNC
     /* Flush the log file after every line so the log isn't lost in a crash */
-    setvbuf(logfile, (char *)NULL, _IOLBF, 0);
+    setbuf(logfile, (char *)NULL);
 #endif
   }
 }

[bagder]

Thanks!

[gvanem]

This issue seems to have surfaced once again. Now in C-ares when CURLDEBUG is in effect.
Turned out to be an user-error; I set %CARES_MEMDEBUG to a non-existing directory/file. I fixed it simply by:

--- a/memdebug.c 2017-05-25 14:03:18
+++ b/memdebug.c 2017-07-06 18:03:24
@@ -115,6 +115,7 @@
       logfile = stderr;
 #ifdef MEMDEBUG_LOG_SYNC
     /* Flush the log file after every line so the log isn't lost in a crash */
+    if (logfile)
        setbuf(logfile, (char *)NULL);
 #endif
   }