New pthread rwlock that is more scalable.

[thirdparty/glibc.git] / nptl / pthread_rwlock_init.c

diff --git a/nptl/pthread_rwlock_init.c b/nptl/pthread_rwlock_init.c
index 7483e5ec4c1d2bdda647a86d6d8d2576e1d2fca7..764ba110fbf50a726570b7f4c5fe7d56c042c6fd 100644 (file)
--- a/nptl/pthread_rwlock_init.c
+++ b/nptl/pthread_rwlock_init.c
@@ -1,4 +1,4 @@
-/* Copyright (C) 2002-2015 Free Software Foundation, Inc.
+/* Copyright (C) 2002-2017 Free Software Foundation, Inc.
    This file is part of the GNU C Library.
    Contributed by Ulrich Drepper <drepper@redhat.com>, 2002.
 
@@ -18,7 +18,6 @@
 
 #include "pthreadP.h"
 #include <string.h>
-#include <kernel-features.h>
 
 
 static const struct pthread_rwlockattr default_rwlockattr =
@@ -28,6 +27,7 @@ static const struct pthread_rwlockattr default_rwlockattr =
   };
 
 
+/* See pthread_rwlock_common.c.  */
 int
 __pthread_rwlock_init (pthread_rwlock_t *rwlock,
                       const pthread_rwlockattr_t *attr)
@@ -38,27 +38,10 @@ __pthread_rwlock_init (pthread_rwlock_t *rwlock,
 
   memset (rwlock, '\0', sizeof (*rwlock));
 
-  rwlock->__data.__flags
-    = iattr->lockkind == PTHREAD_RWLOCK_PREFER_WRITER_NONRECURSIVE_NP;
+  rwlock->__data.__flags = iattr->lockkind;
 
-  /* The __SHARED field is computed to minimize the work that needs to
-     be done while handling the futex.  There are two inputs: the
-     availability of private futexes and whether the rwlock is shared
-     or private.  Unfortunately the value of a private rwlock is
-     fixed: it must be zero.  The PRIVATE_FUTEX flag has the value
-     0x80 in case private futexes are available and zero otherwise.
-     This leads to the following table:
-
-                |     pshared     |     result
-                | shared  private | shared  private |
-     ------------+-----------------+-----------------+
-     !avail 0    |     0       0   |     0       0   |
-      avail 0x80 |  0x80       0   |     0    0x80   |
-
-     If the pshared value is in locking functions XORed with avail
-     we get the expected result.  */
-  rwlock->__data.__shared = (iattr->pshared == PTHREAD_PROCESS_PRIVATE
-                            ? 0 : FUTEX_PRIVATE_FLAG);
+  /* The value of __SHARED in a private rwlock must be zero.  */
+  rwlock->__data.__shared = (iattr->pshared != PTHREAD_PROCESS_PRIVATE);
 
   return 0;
 }