patch-2.3.43 linux/include/asm-ia64/semaphore.h

• Lines: 331
• Date: Sun Feb 6 18:42:40 2000
• Orig file: v2.3.42/linux/include/asm-ia64/semaphore.h
• Orig date: Wed Dec 31 16:00:00 1969

diff -u --recursive --new-file v2.3.42/linux/include/asm-ia64/semaphore.h linux/include/asm-ia64/semaphore.h
@@ -0,0 +1,330 @@
+#ifndef _ASM_IA64_SEMAPHORE_H
+#define _ASM_IA64_SEMAPHORE_H
+
+/*
+ * Copyright (C) 1998-2000 Hewlett-Packard Co
+ * Copyright (C) 1998-2000 David Mosberger-Tang <davidm@hpl.hp.com>
+ */
+
+#include <linux/wait.h>
+
+#include <asm/atomic.h>
+
+struct semaphore {
+	atomic_t count;
+	int sleepers;
+	wait_queue_head_t wait;
+#if WAITQUEUE_DEBUG
+	long __magic;		/* initialized by __SEM_DEBUG_INIT() */
+#endif
+};
+
+#if WAITQUEUE_DEBUG
+# define __SEM_DEBUG_INIT(name)		, (long) &(name).__magic
+#else
+# define __SEM_DEBUG_INIT(name)
+#endif
+
+#define __SEMAPHORE_INITIALIZER(name,count)					\
+{										\
+	ATOMIC_INIT(count), 0, __WAIT_QUEUE_HEAD_INITIALIZER((name).wait)	\
+	__SEM_DEBUG_INIT(name)							\
+}
+
+#define __MUTEX_INITIALIZER(name)	__SEMAPHORE_INITIALIZER(name,1)
+
+#define __DECLARE_SEMAPHORE_GENERIC(name,count)					\
+	struct semaphore name = __SEMAPHORE_INITIALIZER(name, count)
+
+#define DECLARE_MUTEX(name)		__DECLARE_SEMAPHORE_GENERIC(name, 1)
+#define DECLARE_MUTEX_LOCKED(name)	__DECLARE_SEMAPHORE_GENERIC(name, 0)
+
+extern inline void
+sema_init (struct semaphore *sem, int val)
+{
+	*sem = (struct semaphore) __SEMAPHORE_INITIALIZER(*sem, val);
+}
+
+static inline void
+init_MUTEX (struct semaphore *sem)
+{
+	sema_init(sem, 1);
+}
+
+static inline void
+init_MUTEX_LOCKED (struct semaphore *sem)
+{
+	sema_init(sem, 0);
+}
+
+extern void __down (struct semaphore * sem);
+extern int  __down_interruptible (struct semaphore * sem);
+extern int  __down_trylock (struct semaphore * sem);
+extern void __up (struct semaphore * sem);
+
+extern spinlock_t semaphore_wake_lock;
+
+/*
+ * Atomically decrement the semaphore's count.  If it goes negative,
+ * block the calling thread in the TASK_UNINTERRUPTIBLE state.
+ */
+extern inline void
+down (struct semaphore *sem)
+{
+#if WAITQUEUE_DEBUG
+	CHECK_MAGIC(sem->__magic);
+#endif
+	if (atomic_dec_return(&sem->count) < 0)
+		__down(sem);
+}
+
+/*
+ * Atomically decrement the semaphore's count.  If it goes negative,
+ * block the calling thread in the TASK_INTERRUPTIBLE state.
+ */
+extern inline int
+down_interruptible (struct semaphore * sem)
+{
+	int ret = 0;
+
+#if WAITQUEUE_DEBUG
+	CHECK_MAGIC(sem->__magic);
+#endif
+	if (atomic_dec_return(&sem->count) < 0)
+		ret = __down_interruptible(sem);
+	return ret;
+}
+
+extern inline int
+down_trylock (struct semaphore *sem)
+{
+	int ret = 0;
+
+#if WAITQUEUE_DEBUG
+	CHECK_MAGIC(sem->__magic);
+#endif
+	if (atomic_dec_return(&sem->count) < 0)
+		ret = __down_trylock(sem);
+	return ret;
+}
+
+extern inline void
+up (struct semaphore * sem)
+{
+#if WAITQUEUE_DEBUG
+	CHECK_MAGIC(sem->__magic);
+#endif
+	if (atomic_inc_return(&sem->count) <= 0)
+		__up(sem);
+}	
+
+/*
+ * rw mutexes (should that be mutices? =) -- throw rw spinlocks and
+ * semaphores together, and this is what we end up with...
+ *
+ * The lock is initialized to BIAS.  This way, a writer subtracts BIAS
+ * ands gets 0 for the case of an uncontended lock.  Readers decrement
+ * by 1 and see a positive value when uncontended, negative if there
+ * are writers waiting (in which case it goes to sleep).  BIAS must be
+ * chosen such that subtracting BIAS once per CPU will result either
+ * in zero (uncontended case) or in a negative value (contention
+ * case).  On the other hand, BIAS must be at least as big as the
+ * number of processes in the system.
+ *
+ * On IA-64, we use a BIAS value of 0x100000000, which supports up to
+ * 2 billion (2^31) processors and 4 billion processes.
+ *
+ * In terms of fairness, when there is heavy use of the lock, we want
+ * to see the lock being passed back and forth between readers and
+ * writers (like in a producer/consumer style of communication).
+ * 
+
+  For
+ * liveness, it would be necessary to process the blocked readers and
+ * writers in FIFO order.  However, we don't do this (yet).  I suppose
+ * if you have a lock that is _that_ heavily contested, you're in big
+ * trouble anyhow.
+ *
+ *	      -ben (with clarifications & IA-64 comments by davidm)
+ */
+#define RW_LOCK_BIAS		0x100000000ul
+
+struct rw_semaphore {
+	volatile long		count;
+	volatile __u8		write_bias_granted;
+	volatile __u8		read_bias_granted;
+	__u16			pad1;
+	__u32			pad2;
+	wait_queue_head_t	wait;
+	wait_queue_head_t	write_bias_wait;
+#if WAITQUEUE_DEBUG
+	long			__magic;
+	atomic_t		readers;
+	atomic_t		writers;
+#endif
+};
+
+#if WAITQUEUE_DEBUG
+# define __RWSEM_DEBUG_INIT	, ATOMIC_INIT(0), ATOMIC_INIT(0)
+#else
+# define __RWSEM_DEBUG_INIT
+#endif
+
+#define __RWSEM_INITIALIZER(name,count)						\
+{										\
+	(count), 0, 0, 0, 0, __WAIT_QUEUE_HEAD_INITIALIZER((name).wait),	\
+	__WAIT_QUEUE_HEAD_INITIALIZER((name).write_bias_wait)			\
+	__SEM_DEBUG_INIT(name) __RWSEM_DEBUG_INIT				\
+}
+
+#define __DECLARE_RWSEM_GENERIC(name,count)					\
+	struct rw_semaphore name = __RWSEM_INITIALIZER(name,count)
+
+#define DECLARE_RWSEM(name)			__DECLARE_RWSEM_GENERIC(name, RW_LOCK_BIAS)
+#define DECLARE_RWSEM_READ_LOCKED(name)		__DECLARE_RWSEM_GENERIC(name, RW_LOCK_BIAS - 1)
+#define DECLARE_RWSEM_WRITE_LOCKED(name)	__DECLARE_RWSEM_GENERIC(name, 0)
+
+extern void __down_read_failed (struct rw_semaphore *sem, long count);
+extern void __down_write_failed (struct rw_semaphore *sem, long count);
+extern void __rwsem_wake (struct rw_semaphore *sem, long count);
+
+extern inline void
+init_rwsem (struct rw_semaphore *sem)
+{
+	sem->count = RW_LOCK_BIAS;
+	sem->read_bias_granted = 0;
+	sem->write_bias_granted = 0;
+	init_waitqueue_head(&sem->wait);
+	init_waitqueue_head(&sem->write_bias_wait);
+#if WAITQUEUE_DEBUG
+	sem->__magic = (long)&sem->__magic;
+	atomic_set(&sem->readers, 0);
+	atomic_set(&sem->writers, 0);
+#endif
+}
+
+extern inline void
+down_read (struct rw_semaphore *sem)
+{
+	long count;
+
+#if WAITQUEUE_DEBUG
+	CHECK_MAGIC(sem->__magic);
+#endif
+
+	count = ia64_fetch_and_add(-1, &sem->count);
+	if (count < 0)
+		__down_read_failed(sem, count);
+
+#if WAITQUEUE_DEBUG
+	if (sem->write_bias_granted)
+		BUG();
+	if (atomic_read(&sem->writers))
+		BUG();
+	atomic_inc(&sem->readers);
+#endif
+}
+
+extern inline void
+down_write (struct rw_semaphore *sem)
+{
+	long old_count, new_count;
+
+#if WAITQUEUE_DEBUG
+	CHECK_MAGIC(sem->__magic);
+#endif
+
+	do {
+		old_count = sem->count;
+		new_count = old_count - RW_LOCK_BIAS;
+	} while (cmpxchg(&sem->count, old_count, new_count) != old_count);
+
+	if (new_count != 0)
+		__down_write_failed(sem, new_count);
+#if WAITQUEUE_DEBUG
+	if (atomic_read(&sem->writers))
+		BUG();
+	if (atomic_read(&sem->readers))
+		BUG();
+	if (sem->read_bias_granted)
+		BUG();
+	if (sem->write_bias_granted)
+		BUG();
+	atomic_inc(&sem->writers);
+#endif
+}
+
+/*
+ * When a reader does a release, the only significant
+ * case is when there was a writer waiting, and we've
+ * bumped the count to 0: we must wake the writer up.
+ */
+extern inline void
+__up_read (struct rw_semaphore *sem)
+{
+	long count;
+
+	count = ia64_fetch_and_add(1, &sem->count);
+	if (count == 0)
+		/*
+		 * Other processes are blocked already; resolve
+		 * contention by letting either a writer or a reader
+		 * proceed...
+		 */
+		__rwsem_wake(sem, count);
+}
+
+/*
+ * Releasing the writer is easy -- just release it and
+ * wake up any sleepers.
+ */
+extern inline void
+__up_write (struct rw_semaphore *sem)
+{
+	long old_count, new_count;
+
+	do {
+		old_count = sem->count;
+		new_count = old_count + RW_LOCK_BIAS;
+	} while (cmpxchg(&sem->count, old_count, new_count) != old_count);
+
+	/*
+	 * Note: new_count <u RW_LOCK_BIAS <=> old_count < 0 && new_count >= 0.
+	 *	 (where <u is "unsigned less-than").
+	 */
+	if ((unsigned long) new_count < RW_LOCK_BIAS)
+		/* someone is blocked already, resolve contention... */
+		__rwsem_wake(sem, new_count);
+}
+
+extern inline void
+up_read (struct rw_semaphore *sem)
+{
+#if WAITQUEUE_DEBUG
+	if (sem->write_bias_granted)
+		BUG();
+	if (atomic_read(&sem->writers))
+		BUG();
+	atomic_dec(&sem->readers);
+#endif
+	__up_read(sem);
+}
+
+extern inline void
+up_write (struct rw_semaphore *sem)
+{
+#if WAITQUEUE_DEBUG
+	if (sem->read_bias_granted)
+		BUG();
+	if (sem->write_bias_granted)
+		BUG();
+	if (atomic_read(&sem->readers))
+		BUG();
+	if (atomic_read(&sem->writers) != 1)
+		BUG();
+	atomic_dec(&sem->writers);
+#endif
+	__up_write(sem);
+}
+
+#endif /* _ASM_IA64_SEMAPHORE_H */