[PATCH] pthread_once hangs when init routine throws an exception [BZ #18435]

[Martin Sebor <msebor at redhat dot com>]

The C++ 2011 std::call_once function is specified to allow
the initialization routine to exit by throwing an exception.
Such an execution, termed exceptional, requires call_once to
propagate the exception to its caller. A program may contain
any number of exceptional executions but only one returning
execution (which, if it exists, must be the last execution
with the same once flag).

On POSIX systems such as Linux std::call_once is implemented
in terms of pthread_once. However, as discussed in libstdc++
bug 66146 - "call_once not C++11-compliant on ppc64le," GLIBC's
pthread_once hangs when the initialization function exits by
throwing an exception on at least arm and ppc64 (though
apparently not on x86_64). This effectively prevents call_once
from conforming to the C++ requirements since there doesn't
appear to be a thread-safe way to work around this problem in
libstdc++.

The attached patch changes pthread_once to handle gracefully
init functions that exit by throwing exceptions. It has been
tested on ppc64, ppc64le, and x86_64 with no regressions.

During the discussion of the bug concerns were raised about
whether the use case of throwing exceptions from the
pthread_once init routine is intended to be supported either
by POSIX, or by GLIBC. After some research I believe that both
POSIX and GLIBC have, in fact, intended to support it, for at
least two reasons:

First, the POSIX Rationale states in section Thread Cancellation
Overview, under Thread Cancellation Cleanup Handlers, that:

  it is an explicit goal of POSIX.1-2008 to be compatible with
  existing exception facilities and languages having exceptions.

Second, as is evident from the comment above the pthread_once
declaration in GLIBC (quoted below), GLIBC too has intended
to support this use case since 2004 when the comment was
added (and the __THROW specification removed from the API):

   ...
   The initialization functions might throw exception which
   is why this function is not marked with __THROW.  */

Martin

diff --git a/ChangeLog b/ChangeLog
index b7f3c61..c50e380 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,11 @@
+2015-05-31  Martin Sebor  <msebor@redhat.com>
+
+	[BZ #18435]
+	* nptl/Makefile: Add tst-once5.cc.
+	* nptl/pthreadP.h (pthread_cleanup_push, pthread_cleanup_pop):
+	Remove macro redefinitions.
+	* nptl/tst-once5.cc: New test.
+
 2015-05-18  Siddhesh Poyarekar  <siddhesh@redhat.com>
 
 	* .gitignore: Ignore generated *.pyc.
diff --git a/nptl/Makefile b/nptl/Makefile
index d784c8d..1bf35cb 100644
--- a/nptl/Makefile
+++ b/nptl/Makefile
@@ -203,6 +203,7 @@ CFLAGS-send.c = -fexceptions -fasynchronous-unwind-tables
 
 CFLAGS-pt-system.c = -fexceptions
 
+LDFLAGS-tst-once5 = -lstdc++
 
 tests = tst-typesizes \
 	tst-attr1 tst-attr2 tst-attr3 tst-default-attr \
@@ -224,7 +225,7 @@ tests = tst-typesizes \
 	tst-rwlock1 tst-rwlock2 tst-rwlock2a tst-rwlock3 tst-rwlock4 \
 	tst-rwlock5 tst-rwlock6 tst-rwlock7 tst-rwlock8 tst-rwlock9 \
 	tst-rwlock10 tst-rwlock11 tst-rwlock12 tst-rwlock13 tst-rwlock14 \
-	tst-once1 tst-once2 tst-once3 tst-once4 \
+	tst-once1 tst-once2 tst-once3 tst-once4 tst-once5 \
 	tst-key1 tst-key2 tst-key3 tst-key4 \
 	tst-sem1 tst-sem2 tst-sem3 tst-sem4 tst-sem5 tst-sem6 tst-sem7 \
 	tst-sem8 tst-sem9 tst-sem10 tst-sem11 tst-sem12 tst-sem13 tst-sem14 \
diff --git a/nptl/pthreadP.h b/nptl/pthreadP.h
index 84a7105..72d3e23 100644
--- a/nptl/pthreadP.h
+++ b/nptl/pthreadP.h
@@ -536,16 +536,9 @@ extern void __librt_disable_asynccancel (int oldtype)
 extern void __pthread_cleanup_push (struct _pthread_cleanup_buffer *buffer,
 				    void (*routine) (void *), void *arg)
      attribute_hidden;
-# undef pthread_cleanup_push
-# define pthread_cleanup_push(routine,arg) \
-  { struct _pthread_cleanup_buffer _buffer;				      \
-    __pthread_cleanup_push (&_buffer, (routine), (arg));
 
 extern void __pthread_cleanup_pop (struct _pthread_cleanup_buffer *buffer,
 				   int execute) attribute_hidden;
-# undef pthread_cleanup_pop
-# define pthread_cleanup_pop(execute) \
-    __pthread_cleanup_pop (&_buffer, (execute)); }
 #endif
 
 extern void __pthread_cleanup_push_defer (struct _pthread_cleanup_buffer *buffer,
diff --git a/nptl/tst-once5.cc b/nptl/tst-once5.cc
new file mode 100644
index 0000000..60bc78a
--- /dev/null
+++ b/nptl/tst-once5.cc
@@ -0,0 +1,80 @@
+/* Copyright (C) 2015 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+   Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <errno.h>
+#include <pthread.h>
+#include <stdio.h>
+#include <string.h>
+
+
+static pthread_once_t once = PTHREAD_ONCE_INIT;
+
+// Exception type thrown from the pthread_once init routine.
+struct OnceException { };
+
+// Test iteration counter.
+static int niter;
+
+static void
+init_routine (void)
+{
+  if (niter < 2)
+    throw OnceException ();
+}
+
+// Verify that an exception thrown from the pthread_once init routine
+// is propagated to the pthread_once caller and that the function can
+// be subsequently invoked to attempt the initialization again.
+static int
+do_test (void)
+{
+  int result = 1;
+
+  // Repeat three times, having the init routine throw the first two
+  // times and succeed on the final attempt.
+  for (niter = 0; niter != 3; ++niter) {
+
+    try {
+      int rc = pthread_once (&once, init_routine);
+      if (rc)
+        fprintf (stderr, "pthread_once failed: %i (%s)\n",
+                 rc, strerror (rc));
+
+      if (niter < 2)
+        fputs ("pthread_once unexpectedly returned without"
+               " throwing an exception", stderr);
+    }
+    catch (OnceException) {
+      if (1 < niter)
+        fputs ("pthread_once unexpectedly threw", stderr);
+      result = 0;
+    }
+    catch (...) {
+      fputs ("pthread_once threw an unknown exception", stderr);
+    }
+
+    // Abort the test on the first failure.
+    if (result)
+      break;
+  }
+
+  return result;
+}
+
+#define TEST_FUNCTION do_test ()
+#include "../test-skeleton.c"
diff --git a/NEWS b/NEWS
index 8e2976e..a50407f 100644
--- a/NEWS
+++ b/NEWS
@@ -19,7 +19,7 @@ Version 2.22
   18047, 18049, 18068, 18080, 18093, 18100, 18104, 18110, 18111, 18125,
   18128, 18138, 18185, 18196, 18197, 18206, 18210, 18211, 18217, 18220,
   18221, 18234, 18244, 18247, 18287, 18319, 18333, 18346, 18397, 18409,
-  18410, 18412, 18418, 18422, 18434, 18444.
+  18410, 18412, 18418, 18422, 18434, 18444, 18435.
 
 * Cache information can be queried via sysconf() function on s390 e.g. with
   _SC_LEVEL1_ICACHE_SIZE as argument.