We need mutex protection in PerlIOStdio_close() for the duration of

holding our true love file handle open, to stop anything else
temporarily using it for a quick dup() fling, and then closing the
file handle underneath us.
I suspect that the lack of this protection was the cause of the threads
free.t and blocks.t failures on OS X on 5.8.x, where usefaststdio is
the default, and PerlIO is unable to "invalidate" the FILE *.

p4raw-id: //depot/perl@33492

diff --git a/perlio.c b/perlio.c
index 6459a69..a0f96cc 100644 (file)
--- a/perlio.c
+++ b/perlio.c
@@ -3156,8 +3156,26 @@ PerlIOStdio_close(pTHX_ PerlIO *f)
            result = PerlIO_flush(f);
            saveerr = errno;
            invalidate = PerlIOStdio_invalidate_fileno(aTHX_ stdio);
-           if (!invalidate)
+           if (!invalidate) {
                dupfd = PerlLIO_dup(fd);
+#ifdef USE_ITHREADS
+               if (dupfd >= 0) {
+                   /* Right. We need a mutex here because for a brief while we
+                      will have the situation that fd is actually closed.
+                      Hence if a second thread were to get into this block,
+                      its dup() would likely return our fd as its dupfd.
+                      (after all, it is closed). Then if we get to the dup2()
+                      first, we blat the fd back (messing up its temporary as
+                      a side effect) only for it to then close its dupfd
+                      (== our fd) in its close(dupfd) */
+                   MUTEX_LOCK(&PL_perlio_mutex);
+               } else {
+                   /* Oh cXap. This isn't going to go well. Not sure if we can
+                      recover from here, or if closing this particular FILE *
+                      is a good idea now.  */
+               }
+#endif
+           }
        }
         result = PerlSIO_fclose(stdio);
        /* We treat error from stdio as success if we invalidated
@@ -3173,6 +3191,9 @@ PerlIOStdio_close(pTHX_ PerlIO *f)
 #endif
        if (dupfd >= 0) {
            PerlLIO_dup2(dupfd,fd);
+#ifdef USE_ITHREADS
+       MUTEX_UNLOCK(&PL_perlio_mutex);
+#endif
            PerlLIO_close(dupfd);
        }
        return result;