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authorAustin Foxley <austinf@cetoncorp.com>2009-10-17 12:26:24 -0700
committerAustin Foxley <austinf@cetoncorp.com>2009-10-17 12:26:24 -0700
commitc68d0fa2d88fc2134a38d99e7e944828384a7671 (patch)
tree6596943bd1c77f18d6e49d4153ddd3f3d67b49f5 /libpthread/nptl/sysdeps/generic/lowlevellock.h
parent9a03e98a3b418f33c347a6023e9320f3a42cb9e4 (diff)
libpthread/nptl: core of the "Native Posix Threading Library" for uClibc
targetting arm,sh,i386,mips,sparc for now Signed-off-by: Austin Foxley <austinf@cetoncorp.com>
Diffstat (limited to 'libpthread/nptl/sysdeps/generic/lowlevellock.h')
-rw-r--r--libpthread/nptl/sysdeps/generic/lowlevellock.h89
1 files changed, 89 insertions, 0 deletions
diff --git a/libpthread/nptl/sysdeps/generic/lowlevellock.h b/libpthread/nptl/sysdeps/generic/lowlevellock.h
new file mode 100644
index 000000000..7f95daada
--- /dev/null
+++ b/libpthread/nptl/sysdeps/generic/lowlevellock.h
@@ -0,0 +1,89 @@
+/* Copyright (C) 2002 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, write to the Free
+ Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
+ 02111-1307 USA. */
+
+#include <atomic.h>
+
+
+/* Implement generic mutex. Basic futex syscall support is required:
+
+ lll_futex_wait(futex, value) - call sys_futex with FUTEX_WAIT
+ and third parameter VALUE
+
+ lll_futex_wake(futex, value) - call sys_futex with FUTEX_WAKE
+ and third parameter VALUE
+*/
+
+
+/* Mutex lock counter:
+ bit 31 clear means unlocked;
+ bit 31 set means locked.
+
+ All code that looks at bit 31 first increases the 'number of
+ interested threads' usage counter, which is in bits 0-30.
+
+ All negative mutex values indicate that the mutex is still locked. */
+
+
+static inline void
+__generic_mutex_lock (int *mutex)
+{
+ unsigned int v;
+
+ /* Bit 31 was clear, we got the mutex. (this is the fastpath). */
+ if (atomic_bit_test_set (mutex, 31) == 0)
+ return;
+
+ atomic_increment (mutex);
+
+ while (1)
+ {
+ if (atomic_bit_test_set (mutex, 31) == 0)
+ {
+ atomic_decrement (mutex);
+ return;
+ }
+
+ /* We have to wait now. First make sure the futex value we are
+ monitoring is truly negative (i.e. locked). */
+ v = *mutex;
+ if (v >= 0)
+ continue;
+
+ lll_futex_wait (mutex, v);
+ }
+}
+
+
+static inline void
+__generic_mutex_unlock (int *mutex)
+{
+ /* Adding 0x80000000 to the counter results in 0 if and only if
+ there are not other interested threads - we can return (this is
+ the fastpath). */
+ if (atomic_add_zero (mutex, 0x80000000))
+ return;
+
+ /* There are other threads waiting for this mutex, wake one of them
+ up. */
+ lll_futex_wake (mutex, 1);
+}
+
+
+#define lll_mutex_lock(futex) __generic_mutex_lock (&(futex))
+#define lll_mutex_unlock(futex) __generic_mutex_unlock (&(futex))