1 files changed, 100 insertions, 0 deletions
diff --git a/REORG.TODO/nptl/pthread_cond_signal.c b/REORG.TODO/nptl/pthread_cond_signal.c
new file mode 100644
index 0000000000..db0698c66c
--- /dev/null
+++ b/REORG.TODO/nptl/pthread_cond_signal.c
@@ -0,0 +1,100 @@
+/* Copyright (C) 2003-2017 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+   Contributed by Martin Schwidefsky <schwidefsky@de.ibm.com>, 2003.
+
+   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 <endian.h>
+#include <errno.h>
+#include <sysdep.h>
+#include <futex-internal.h>
+#include <pthread.h>
+#include <pthreadP.h>
+#include <atomic.h>
+#include <stdint.h>
+
+#include <shlib-compat.h>
+#include <stap-probe.h>
+
+#include "pthread_cond_common.c"
+
+/* See __pthread_cond_wait for a high-level description of the algorithm.  */
+int
+__pthread_cond_signal (pthread_cond_t *cond)
+{
+  LIBC_PROBE (cond_signal, 1, cond);
+
+  /* First check whether there are waiters.  Relaxed MO is fine for that for
+     the same reasons that relaxed MO is fine when observing __wseq (see
+     below).  */
+  unsigned int wrefs = atomic_load_relaxed (&cond->__data.__wrefs);
+  if (wrefs >> 3 == 0)
+    return 0;
+  int private = __condvar_get_private (wrefs);
+
+  __condvar_acquire_lock (cond, private);
+
+  /* Load the waiter sequence number, which represents our relative ordering
+     to any waiters.  Relaxed MO is sufficient for that because:
+     1) We can pick any position that is allowed by external happens-before
+        constraints.  In particular, if another __pthread_cond_wait call
+        happened before us, this waiter must be eligible for being woken by
+        us.  The only way do establish such a happens-before is by signaling
+        while having acquired the mutex associated with the condvar and
+        ensuring that the signal's critical section happens after the waiter.
+        Thus, the mutex ensures that we see that waiter's __wseq increase.
+     2) Once we pick a position, we do not need to communicate this to the
+        program via a happens-before that we set up: First, any wake-up could
+        be a spurious wake-up, so the program must not interpret a wake-up as
+        an indication that the waiter happened before a particular signal;
+        second, a program cannot detect whether a waiter has not yet been
+        woken (i.e., it cannot distinguish between a non-woken waiter and one
+        that has been woken but hasn't resumed execution yet), and thus it
+        cannot try to deduce that a signal happened before a particular
+        waiter.  */
+  unsigned long long int wseq = __condvar_load_wseq_relaxed (cond);
+  unsigned int g1 = (wseq & 1) ^ 1;
+  wseq >>= 1;
+  bool do_futex_wake = false;
+
+  /* If G1 is still receiving signals, we put the signal there.  If not, we
+     check if G2 has waiters, and if so, quiesce and switch G1 to the former
+     G2; if this results in a new G1 with waiters (G2 might have cancellations
+     already, see __condvar_quiesce_and_switch_g1), we put the signal in the
+     new G1.  */
+  if ((cond->__data.__g_size[g1] != 0)
+      || __condvar_quiesce_and_switch_g1 (cond, wseq, &g1, private))
+    {
+      /* Add a signal.  Relaxed MO is fine because signaling does not need to
+	 establish a happens-before relation (see above).  We do not mask the
+	 release-MO store when initializing a group in
+	 __condvar_quiesce_and_switch_g1 because we use an atomic
+	 read-modify-write and thus extend that store's release sequence.  */
+      atomic_fetch_add_relaxed (cond->__data.__g_signals + g1, 2);
+      cond->__data.__g_size[g1]--;
+      /* TODO Only set it if there are indeed futex waiters.  */
+      do_futex_wake = true;
+    }
+
+  __condvar_release_lock (cond, private);
+
+  if (do_futex_wake)
+    futex_wake (cond->__data.__g_signals + g1, 1, private);
+
+  return 0;
+}
+
+versioned_symbol (libpthread, __pthread_cond_signal, pthread_cond_signal,
+		  GLIBC_2_3_2);