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
|
/**
* xrdp: A Remote Desktop Protocol server.
*
* Copyright (C) Jay Sorg 2004-2012
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*
* session manager
* linux only
*/
#include "libscp_lock.h"
#include <semaphore.h>
#include <pthread.h>
pthread_mutex_t lock_fork; /* this lock protects the counters */
pthread_mutexattr_t lock_fork_attr; /* mutex attributes */
sem_t lock_fork_req; /* semaphore on which the process that are going to fork suspend on */
sem_t lock_fork_wait; /* semaphore on which the suspended process wait on */
int lock_fork_forkers_count; /* threads that want to fork */
int lock_fork_blockers_count; /* threads thar are blocking fork */
int lock_fork_waiting_count; /* threads suspended until the fork finishes */
void DEFAULT_CC
scp_lock_init(void)
{
/* initializing fork lock */
pthread_mutexattr_init(&lock_fork_attr);
pthread_mutex_init(&lock_fork, &lock_fork_attr);
sem_init(&lock_fork_req, 0, 0);
sem_init(&lock_fork_wait, 0, 0);
/* here we don't use locking because lock_init() should be called BEFORE */
/* any thread is created */
lock_fork_blockers_count = 0;
lock_fork_waiting_count = 0;
lock_fork_forkers_count = 0;
}
/******************************************************************************/
void DEFAULT_CC
scp_lock_fork_request(void)
{
/* lock mutex */
pthread_mutex_lock(&lock_fork);
if (lock_fork_blockers_count == 0)
{
/* if noone is blocking fork(), then we're allowed to fork */
sem_post(&lock_fork_req);
}
lock_fork_forkers_count++;
pthread_mutex_unlock(&lock_fork);
/* we wait to be allowed to fork() */
sem_wait(&lock_fork_req);
}
/******************************************************************************/
void DEFAULT_CC
scp_lock_fork_release(void)
{
pthread_mutex_lock(&lock_fork);
lock_fork_forkers_count--;
/* if there's someone else that want to fork, we let him fork() */
if (lock_fork_forkers_count > 0)
{
sem_post(&lock_fork_req);
}
for (; lock_fork_waiting_count > 0; lock_fork_waiting_count--)
{
/* waking up the other processes */
sem_post(&lock_fork_wait);
}
pthread_mutex_unlock(&lock_fork);
}
/******************************************************************************/
void DEFAULT_CC
scp_lock_fork_critical_section_end(int blocking)
{
//LOG_DBG("lock_fork_critical_secection_end()",0);
/* lock mutex */
pthread_mutex_lock(&lock_fork);
if (blocking == LIBSCP_LOCK_FORK_BLOCKER)
{
lock_fork_blockers_count--;
}
/* if there's someone who wants to fork and we're the last blocking */
/* then we let him go */
if ((lock_fork_blockers_count == 0) && (lock_fork_forkers_count > 0))
{
sem_post(&lock_fork_req);
}
pthread_mutex_unlock(&lock_fork);
}
/******************************************************************************/
int DEFAULT_CC
scp_lock_fork_critical_section_start(void)
{
//LOG_DBG("lock_fork_critical_secection_start()",0);
do
{
pthread_mutex_lock(&lock_fork);
/* someone requested to fork */
if (lock_fork_forkers_count > 0)
{
lock_fork_waiting_count++;
pthread_mutex_unlock(&lock_fork);
/* we wait until the fork finishes */
sem_wait(&lock_fork_wait);
}
else
{
/* no fork, so we can go on... */
lock_fork_blockers_count++;
pthread_mutex_unlock(&lock_fork);
return LIBSCP_LOCK_FORK_BLOCKER;
}
}
while (1);
/* we'll never get here */
return LIBSCP_LOCK_FORK_WAITING;
}
|
