1/*
2 * Copyright 2009, Michael Lotz, mmlr@mlotz.ch.
3 * Copyright 2008-2010, Ingo Weinhold, ingo_weinhold@gmx.de.
4 * Copyright 2002-2009, Axel Dörfler, axeld@pinc-software.de. All rights reserved.
5 * Distributed under the terms of the MIT License.
6 *
7 * Copyright 2001-2002, Travis Geiselbrecht. All rights reserved.
8 * Distributed under the terms of the NewOS License.
9 */
10
11
12#include <locks.h>
13
14#include <stdlib.h>
15#include <string.h>
16
17#include <syscalls.h>
18#include <user_mutex_defs.h>
19
20
21#define MAX_UNSUCCESSFUL_SPINS	100
22
23
24extern int32 __gCPUCount;
25
26
27// #pragma mark - mutex
28
29
30void
31__mutex_init(mutex *lock, const char *name)
32{
33	lock->name = name;
34	lock->lock = 0;
35	lock->flags = 0;
36}
37
38
39void
40__mutex_init_etc(mutex *lock, const char *name, uint32 flags)
41{
42	lock->name = (flags & MUTEX_FLAG_CLONE_NAME) != 0 ? strdup(name) : name;
43	lock->lock = 0;
44	lock->flags = flags;
45
46	if (__gCPUCount < 2)
47		lock->flags &= ~uint32(MUTEX_FLAG_ADAPTIVE);
48}
49
50
51void
52__mutex_destroy(mutex *lock)
53{
54	if ((lock->flags & MUTEX_FLAG_CLONE_NAME) != 0)
55		free(const_cast<char*>(lock->name));
56}
57
58
59status_t
60__mutex_lock(mutex *lock)
61{
62	uint32 count = 0;
63	const uint32 kMaxCount
64		= (lock->flags & MUTEX_FLAG_ADAPTIVE) != 0 ? MAX_UNSUCCESSFUL_SPINS : 1;
65
66	int32 oldValue;
67	do {
68		// set the locked flag
69		oldValue = atomic_or(&lock->lock, B_USER_MUTEX_LOCKED);
70
71		if ((oldValue & (B_USER_MUTEX_LOCKED | B_USER_MUTEX_WAITING)) == 0
72				|| (oldValue & B_USER_MUTEX_DISABLED) != 0) {
73			// No one has the lock or is waiting for it, or the mutex has been
74			// disabled.
75			return B_OK;
76		}
77	} while (count++ < kMaxCount && (oldValue & B_USER_MUTEX_WAITING) != 0);
78
79	// we have to call the kernel
80	status_t error;
81	do {
82		error = _kern_mutex_lock(&lock->lock, lock->name, 0, 0);
83	} while (error == B_INTERRUPTED);
84
85	return error;
86}
87
88
89void
90__mutex_unlock(mutex *lock)
91{
92	// clear the locked flag
93	int32 oldValue = atomic_and(&lock->lock, ~(int32)B_USER_MUTEX_LOCKED);
94	if ((oldValue & B_USER_MUTEX_WAITING) != 0
95			&& (oldValue & B_USER_MUTEX_DISABLED) == 0) {
96		_kern_mutex_unlock(&lock->lock, 0);
97	}
98}
99