1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
|
// Copyright 2011 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// +build freebsd linux
#include "runtime.h"
// This implementation depends on OS-specific implementations of
//
// runtime_futexsleep(uint32 *addr, uint32 val, int64 ns)
// Atomically,
// if(*addr == val) sleep
// Might be woken up spuriously; that's allowed.
// Don't sleep longer than ns; ns < 0 means forever.
//
// runtime_futexwakeup(uint32 *addr, uint32 cnt)
// If any procs are sleeping on addr, wake up at most cnt.
enum
{
MUTEX_UNLOCKED = 0,
MUTEX_LOCKED = 1,
MUTEX_SLEEPING = 2,
ACTIVE_SPIN = 4,
ACTIVE_SPIN_CNT = 30,
PASSIVE_SPIN = 1,
};
// Possible lock states are MUTEX_UNLOCKED, MUTEX_LOCKED and MUTEX_SLEEPING.
// MUTEX_SLEEPING means that there is presumably at least one sleeping thread.
// Note that there can be spinning threads during all states - they do not
// affect mutex's state.
void
runtime_lock(Lock *l)
{
uint32 i, v, wait, spin;
if(runtime_m()->locks++ < 0)
runtime_throw("runtime_lock: lock count");
// Speculative grab for lock.
v = runtime_xchg(&l->key, MUTEX_LOCKED);
if(v == MUTEX_UNLOCKED)
return;
// wait is either MUTEX_LOCKED or MUTEX_SLEEPING
// depending on whether there is a thread sleeping
// on this mutex. If we ever change l->key from
// MUTEX_SLEEPING to some other value, we must be
// careful to change it back to MUTEX_SLEEPING before
// returning, to ensure that the sleeping thread gets
// its wakeup call.
wait = v;
// On uniprocessor's, no point spinning.
// On multiprocessors, spin for ACTIVE_SPIN attempts.
spin = 0;
if(runtime_ncpu > 1)
spin = ACTIVE_SPIN;
for(;;) {
// Try for lock, spinning.
for(i = 0; i < spin; i++) {
while(l->key == MUTEX_UNLOCKED)
if(runtime_cas(&l->key, MUTEX_UNLOCKED, wait))
return;
runtime_procyield(ACTIVE_SPIN_CNT);
}
// Try for lock, rescheduling.
for(i=0; i < PASSIVE_SPIN; i++) {
while(l->key == MUTEX_UNLOCKED)
if(runtime_cas(&l->key, MUTEX_UNLOCKED, wait))
return;
runtime_osyield();
}
// Sleep.
v = runtime_xchg(&l->key, MUTEX_SLEEPING);
if(v == MUTEX_UNLOCKED)
return;
wait = MUTEX_SLEEPING;
runtime_futexsleep(&l->key, MUTEX_SLEEPING, -1);
}
}
void
runtime_unlock(Lock *l)
{
uint32 v;
if(--runtime_m()->locks < 0)
runtime_throw("runtime_unlock: lock count");
v = runtime_xchg(&l->key, MUTEX_UNLOCKED);
if(v == MUTEX_UNLOCKED)
runtime_throw("unlock of unlocked lock");
if(v == MUTEX_SLEEPING)
runtime_futexwakeup(&l->key, 1);
}
// One-time notifications.
void
runtime_noteclear(Note *n)
{
n->key = 0;
}
void
runtime_notewakeup(Note *n)
{
if(runtime_xchg(&n->key, 1))
runtime_throw("notewakeup - double wakeup");
runtime_futexwakeup(&n->key, 1);
}
void
runtime_notesleep(Note *n)
{
if(runtime_m()->profilehz > 0)
runtime_setprof(false);
while(runtime_atomicload(&n->key) == 0)
runtime_futexsleep(&n->key, 0, -1);
if(runtime_m()->profilehz > 0)
runtime_setprof(true);
}
void
runtime_notetsleep(Note *n, int64 ns)
{
int64 deadline, now;
if(ns < 0) {
runtime_notesleep(n);
return;
}
if(runtime_atomicload(&n->key) != 0)
return;
if(runtime_m()->profilehz > 0)
runtime_setprof(false);
deadline = runtime_nanotime() + ns;
for(;;) {
runtime_futexsleep(&n->key, 0, ns);
if(runtime_atomicload(&n->key) != 0)
break;
now = runtime_nanotime();
if(now >= deadline)
break;
ns = deadline - now;
}
if(runtime_m()->profilehz > 0)
runtime_setprof(true);
}
|
