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-rwxr-xr-xlibraries/sqlite/win32/mutex_unix.c223
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1/*
2** 2007 August 28
3**
4** The author disclaims copyright to this source code. In place of
5** a legal notice, here is a blessing:
6**
7** May you do good and not evil.
8** May you find forgiveness for yourself and forgive others.
9** May you share freely, never taking more than you give.
10**
11*************************************************************************
12** This file contains the C functions that implement mutexes for pthreads
13**
14** $Id: mutex_unix.c,v 1.2 2007/08/28 22:24:35 drh Exp $
15*/
16#include "sqliteInt.h"
17
18/*
19** The code in this file is only used if we are compiling threadsafe
20** under unix with pthreads.
21**
22** Note that this implementation requires a version of pthreads that
23** supports recursive mutexes.
24*/
25#ifdef SQLITE_MUTEX_PTHREADS
26
27#include <pthread.h>
28
29/*
30** Each recursive mutex is an instance of the following structure.
31*/
32struct sqlite3_mutex {
33 pthread_mutex_t mutex; /* Mutex controlling the lock */
34 int id; /* Mutex type */
35 int nRef; /* Number of entrances */
36 pthread_t owner; /* Thread that is within this mutex */
37#ifdef SQLITE_DEBUG
38 int trace; /* True to trace changes */
39#endif
40};
41
42/*
43** The sqlite3_mutex_alloc() routine allocates a new
44** mutex and returns a pointer to it. If it returns NULL
45** that means that a mutex could not be allocated. SQLite
46** will unwind its stack and return an error. The argument
47** to sqlite3_mutex_alloc() is one of these integer constants:
48**
49** <ul>
50** <li> SQLITE_MUTEX_FAST
51** <li> SQLITE_MUTEX_RECURSIVE
52** <li> SQLITE_MUTEX_STATIC_MASTER
53** <li> SQLITE_MUTEX_STATIC_MEM
54** <li> SQLITE_MUTEX_STATIC_MEM2
55** <li> SQLITE_MUTEX_STATIC_PRNG
56** <li> SQLITE_MUTEX_STATIC_LRU
57** </ul>
58**
59** The first two constants cause sqlite3_mutex_alloc() to create
60** a new mutex. The new mutex is recursive when SQLITE_MUTEX_RECURSIVE
61** is used but not necessarily so when SQLITE_MUTEX_FAST is used.
62** The mutex implementation does not need to make a distinction
63** between SQLITE_MUTEX_RECURSIVE and SQLITE_MUTEX_FAST if it does
64** not want to. But SQLite will only request a recursive mutex in
65** cases where it really needs one. If a faster non-recursive mutex
66** implementation is available on the host platform, the mutex subsystem
67** might return such a mutex in response to SQLITE_MUTEX_FAST.
68**
69** The other allowed parameters to sqlite3_mutex_alloc() each return
70** a pointer to a static preexisting mutex. Three static mutexes are
71** used by the current version of SQLite. Future versions of SQLite
72** may add additional static mutexes. Static mutexes are for internal
73** use by SQLite only. Applications that use SQLite mutexes should
74** use only the dynamic mutexes returned by SQLITE_MUTEX_FAST or
75** SQLITE_MUTEX_RECURSIVE.
76**
77** Note that if one of the dynamic mutex parameters (SQLITE_MUTEX_FAST
78** or SQLITE_MUTEX_RECURSIVE) is used then sqlite3_mutex_alloc()
79** returns a different mutex on every call. But for the static
80** mutex types, the same mutex is returned on every call that has
81** the same type number.
82*/
83sqlite3_mutex *sqlite3_mutex_alloc(int iType){
84 static sqlite3_mutex staticMutexes[] = {
85 { PTHREAD_MUTEX_INITIALIZER, },
86 { PTHREAD_MUTEX_INITIALIZER, },
87 { PTHREAD_MUTEX_INITIALIZER, },
88 { PTHREAD_MUTEX_INITIALIZER, },
89 { PTHREAD_MUTEX_INITIALIZER, },
90 };
91 sqlite3_mutex *p;
92 switch( iType ){
93 case SQLITE_MUTEX_RECURSIVE: {
94 p = sqlite3MallocZero( sizeof(*p) );
95 if( p ){
96 pthread_mutexattr_t recursiveAttr;
97 pthread_mutexattr_init(&recursiveAttr);
98 pthread_mutexattr_settype(&recursiveAttr, PTHREAD_MUTEX_RECURSIVE);
99 pthread_mutex_init(&p->mutex, &recursiveAttr);
100 pthread_mutexattr_destroy(&recursiveAttr);
101 p->id = iType;
102 }
103 break;
104 }
105 case SQLITE_MUTEX_FAST: {
106 p = sqlite3MallocZero( sizeof(*p) );
107 if( p ){
108 p->id = iType;
109 pthread_mutex_init(&p->mutex, 0);
110 }
111 break;
112 }
113 default: {
114 assert( iType-2 >= 0 );
115 assert( iType-2 < sizeof(staticMutexes)/sizeof(staticMutexes[0]) );
116 p = &staticMutexes[iType-2];
117 p->id = iType;
118 break;
119 }
120 }
121 return p;
122}
123
124
125/*
126** This routine deallocates a previously
127** allocated mutex. SQLite is careful to deallocate every
128** mutex that it allocates.
129*/
130void sqlite3_mutex_free(sqlite3_mutex *p){
131 assert( p );
132 assert( p->nRef==0 );
133 assert( p->id==SQLITE_MUTEX_FAST || p->id==SQLITE_MUTEX_RECURSIVE );
134 pthread_mutex_destroy(&p->mutex);
135 sqlite3_free(p);
136}
137
138/*
139** The sqlite3_mutex_enter() and sqlite3_mutex_try() routines attempt
140** to enter a mutex. If another thread is already within the mutex,
141** sqlite3_mutex_enter() will block and sqlite3_mutex_try() will return
142** SQLITE_BUSY. The sqlite3_mutex_try() interface returns SQLITE_OK
143** upon successful entry. Mutexes created using SQLITE_MUTEX_RECURSIVE can
144** be entered multiple times by the same thread. In such cases the,
145** mutex must be exited an equal number of times before another thread
146** can enter. If the same thread tries to enter any other kind of mutex
147** more than once, the behavior is undefined.
148*/
149void sqlite3_mutex_enter(sqlite3_mutex *p){
150 assert( p );
151 assert( p->id==SQLITE_MUTEX_RECURSIVE || sqlite3_mutex_notheld(p) );
152 pthread_mutex_lock(&p->mutex);
153 p->owner = pthread_self();
154 p->nRef++;
155#ifdef SQLITE_DEBUG
156 if( p->trace ){
157 printf("enter mutex %p (%d) with nRef=%d\n", p, p->trace, p->nRef);
158 }
159#endif
160}
161int sqlite3_mutex_try(sqlite3_mutex *p){
162 int rc;
163 assert( p );
164 assert( p->id==SQLITE_MUTEX_RECURSIVE || sqlite3_mutex_notheld(p) );
165 if( pthread_mutex_trylock(&p->mutex)==0 ){
166 p->owner = pthread_self();
167 p->nRef++;
168 rc = SQLITE_OK;
169#ifdef SQLITE_DEBUG
170 if( p->trace ){
171 printf("enter mutex %p (%d) with nRef=%d\n", p, p->trace, p->nRef);
172 }
173#endif
174 }else{
175 rc = SQLITE_BUSY;
176 }
177 return rc;
178}
179
180/*
181** The sqlite3_mutex_leave() routine exits a mutex that was
182** previously entered by the same thread. The behavior
183** is undefined if the mutex is not currently entered or
184** is not currently allocated. SQLite will never do either.
185*/
186void sqlite3_mutex_leave(sqlite3_mutex *p){
187 assert( p );
188 assert( sqlite3_mutex_held(p) );
189 p->nRef--;
190 assert( p->nRef==0 || p->id==SQLITE_MUTEX_RECURSIVE );
191#ifdef SQLITE_DEBUG
192 if( p->trace ){
193 printf("leave mutex %p (%d) with nRef=%d\n", p, p->trace, p->nRef);
194 }
195#endif
196 pthread_mutex_unlock(&p->mutex);
197}
198
199/*
200** The sqlite3_mutex_held() and sqlite3_mutex_notheld() routine are
201** intended for use only inside assert() statements. On some platforms,
202** there might be race conditions that can cause these routines to
203** deliver incorrect results. In particular, if pthread_equal() is
204** not an atomic operation, then these routines might delivery
205** incorrect results. On most platforms, pthread_equal() is a
206** comparison of two integers and is therefore atomic. But we are
207** told that HPUX is not such a platform. If so, then these routines
208** will not always work correctly on HPUX.
209**
210** On those platforms where pthread_equal() is not atomic, SQLite
211** should be compiled without -DSQLITE_DEBUG and with -DNDEBUG to
212** make sure no assert() statements are evaluated and hence these
213** routines are never called.
214*/
215#ifndef NDEBUG
216int sqlite3_mutex_held(sqlite3_mutex *p){
217 return p==0 || (p->nRef!=0 && pthread_equal(p->owner, pthread_self()));
218}
219int sqlite3_mutex_notheld(sqlite3_mutex *p){
220 return p==0 || p->nRef==0 || pthread_equal(p->owner, pthread_self())==0;
221}
222#endif
223#endif /* SQLITE_MUTEX_PTHREAD */
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