Update copyright dates with scripts/update-copyrights.

[thirdparty/glibc.git] / sysdeps / unix / sysv / linux / powerpc / force-elision.h

diff --git a/sysdeps/unix/sysv/linux/powerpc/force-elision.h b/sysdeps/unix/sysv/linux/powerpc/force-elision.h
index 318f7915c7f84a1a0b7659b842b6ce3ea227693c..b1532bef0580dd515fa9bcc5dc4810b6f2c57a73 100644 (file)
--- a/sysdeps/unix/sysv/linux/powerpc/force-elision.h
+++ b/sysdeps/unix/sysv/linux/powerpc/force-elision.h
@@ -1,5 +1,5 @@
 /* force-elision.h: Automatic enabling of elision for mutexes
-   Copyright (C) 2015-2017 Free Software Foundation, Inc.
+   Copyright (C) 2015-2019 Free Software Foundation, Inc.
    This file is part of the GNU C Library.
 
    The GNU C Library is free software; you can redistribute it and/or
@@ -16,13 +16,47 @@
    License along with the GNU C Library; if not, see
    <http://www.gnu.org/licenses/>.  */
 
-#ifdef ENABLE_LOCK_ELISION
 /* Automatically enable elision for existing user lock kinds.  */
 #define FORCE_ELISION(m, s)                                            \
-  if (__pthread_force_elision                                          \
-      && (m->__data.__kind & PTHREAD_MUTEX_ELISION_FLAGS_NP) == 0)     \
+  if (__pthread_force_elision)                                         \
     {                                                                  \
-      mutex->__data.__kind |= PTHREAD_MUTEX_ELISION_NP;                        \
-      s;                                                               \
+      /* See concurrency notes regarding __kind in                     \
+        struct __pthread_mutex_s in                                    \
+        sysdeps/nptl/bits/thread-shared-types.h.                       \
+                                                                       \
+        There are the following cases for the kind of a mutex          \
+        (The mask PTHREAD_MUTEX_ELISION_FLAGS_NP covers the flags      \
+        PTHREAD_MUTEX_ELISION_NP and PTHREAD_MUTEX_NO_ELISION_NP where \
+        only one of both flags can be set):                            \
+        - both flags are not set:                                      \
+        This is the first lock operation for this mutex.  Enable       \
+        elision as it is not enabled so far.                           \
+        Note: It can happen that multiple threads are calling e.g.     \
+        pthread_mutex_lock at the same time as the first lock          \
+        operation for this mutex.  Then elision is enabled for this    \
+        mutex by multiple threads.  Storing with relaxed MO is enough  \
+        as all threads will store the same new value for the kind of   \
+        the mutex.  But we have to ensure that we always use the       \
+        elision path regardless if this thread has enabled elision or  \
+        another one.                                                   \
+                                                                       \
+        - PTHREAD_MUTEX_ELISION_NP flag is set:                        \
+        Elision was already enabled for this mutex by a previous lock  \
+        operation.  See case above.  Just use the elision path.        \
+                                                                       \
+        - PTHREAD_MUTEX_NO_ELISION_NP flag is set:                     \
+        Elision was explicitly disabled by pthread_mutexattr_settype.  \
+        Do not use the elision path.                                   \
+        Note: The flag PTHREAD_MUTEX_NO_ELISION_NP will never be       \
+        changed after mutex initialization.  */                        \
+      int mutex_kind = atomic_load_relaxed (&((m)->__data.__kind));    \
+      if ((mutex_kind & PTHREAD_MUTEX_ELISION_FLAGS_NP) == 0)          \
+       {                                                               \
+         mutex_kind |= PTHREAD_MUTEX_ELISION_NP;                       \
+         atomic_store_relaxed (&((m)->__data.__kind), mutex_kind);     \
+       }                                                               \
+      if ((mutex_kind & PTHREAD_MUTEX_ELISION_NP) != 0)                        \
+       {                                                               \
+         s;                                                            \
+       }                                                               \
     }
-#endif