3 ** This is an improved implementation of Reader/Writer locks does
4 ** not protect writers from starvation. That is, if a writer is
5 ** currently waiting on a reader, any new reader will get
6 ** the lock before the writer.
8 ** Does not support cancellation nor does any status checking.
10 /* Adapted from publically available examples for:
11 * "Programming with Posix Threads"
12 * by David R Butenhof, Addison-Wesley
13 * http://cseng.aw.com/bookpage.taf?ISBN=0-201-63392-2
18 #include <ac/stdlib.h>
21 #include <ac/string.h>
23 #include "ldap_pvt_thread.h"
26 * implementations that provide their own compatible
27 * reader/writer locks define LDAP_THREAD_HAVE_RDWR
28 * in ldap_pvt_thread.h
30 #ifndef LDAP_THREAD_HAVE_RDWR
33 ldap_pvt_thread_rdwr_init( ldap_pvt_thread_rdwr_t *rw )
37 memset( rw, 0, sizeof(ldap_pvt_thread_rdwr_t) );
39 /* we should check return results */
40 ldap_pvt_thread_mutex_init( &rw->ltrw_mutex );
41 ldap_pvt_thread_cond_init( &rw->ltrw_read );
42 ldap_pvt_thread_cond_init( &rw->ltrw_write );
44 rw->ltrw_valid = LDAP_PVT_THREAD_RDWR_VALID;
49 ldap_pvt_thread_rdwr_destroy( ldap_pvt_thread_rdwr_t *rw )
52 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
54 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALID )
55 return LDAP_PVT_THREAD_EINVAL;
57 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
60 if( rw->ltrw_r_active > 0 || rw->ltrw_w_active > 0) {
61 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
62 return LDAP_PVT_THREAD_EBUSY;
65 /* waiting threads? */
66 if( rw->ltrw_r_wait > 0 || rw->ltrw_w_wait > 0) {
67 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
68 return LDAP_PVT_THREAD_EBUSY;
73 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
75 ldap_pvt_thread_mutex_destroy( &rw->ltrw_mutex );
76 ldap_pvt_thread_cond_destroy( &rw->ltrw_read );
77 ldap_pvt_thread_cond_destroy( &rw->ltrw_write );
82 int ldap_pvt_thread_rdwr_rlock( ldap_pvt_thread_rdwr_t *rw )
85 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
87 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALID )
88 return LDAP_PVT_THREAD_EINVAL;
90 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
92 if( rw->ltrw_w_active > 0 ) {
93 /* writer is active */
98 ldap_pvt_thread_cond_wait(
99 &rw->ltrw_read, &rw->ltrw_mutex );
100 } while( rw->ltrw_w_active > 0 );
107 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
112 int ldap_pvt_thread_rdwr_rtrylock( ldap_pvt_thread_rdwr_t *rw )
114 assert( rw != NULL );
115 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
117 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALID )
118 return LDAP_PVT_THREAD_EINVAL;
120 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
122 if( rw->ltrw_w_active > 0) {
123 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
124 return LDAP_PVT_THREAD_EBUSY;
129 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
134 int ldap_pvt_thread_rdwr_runlock( ldap_pvt_thread_rdwr_t *rw )
136 assert( rw != NULL );
137 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
139 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALID )
140 return LDAP_PVT_THREAD_EINVAL;
142 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
146 if (rw->ltrw_r_active == 0 && rw->ltrw_w_wait > 0 ) {
147 ldap_pvt_thread_cond_signal( &rw->ltrw_write );
150 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
155 int ldap_pvt_thread_rdwr_wlock( ldap_pvt_thread_rdwr_t *rw )
157 assert( rw != NULL );
158 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
160 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALID )
161 return LDAP_PVT_THREAD_EINVAL;
163 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
165 if ( rw->ltrw_w_active > 0 || rw->ltrw_r_active > 0 ) {
169 ldap_pvt_thread_cond_wait(
170 &rw->ltrw_write, &rw->ltrw_mutex );
171 } while ( rw->ltrw_w_active > 0 || rw->ltrw_r_active > 0 );
178 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
183 int ldap_pvt_thread_rdwr_wtrylock( ldap_pvt_thread_rdwr_t *rw )
185 assert( rw != NULL );
186 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
188 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALID )
189 return LDAP_PVT_THREAD_EINVAL;
191 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
193 if ( rw->ltrw_w_active > 0 || rw->ltrw_r_active > 0 ) {
194 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
195 return LDAP_PVT_THREAD_EBUSY;
200 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
205 int ldap_pvt_thread_rdwr_wunlock( ldap_pvt_thread_rdwr_t *rw )
207 assert( rw != NULL );
208 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
210 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALID )
211 return LDAP_PVT_THREAD_EINVAL;
213 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
217 if (rw->ltrw_r_wait > 0) {
218 ldap_pvt_thread_cond_broadcast( &rw->ltrw_read );
220 } else if (rw->ltrw_w_wait > 0) {
221 ldap_pvt_thread_cond_signal( &rw->ltrw_write );
224 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
229 #ifdef LDAP_RDWR_DEBUG
232 * return 0 if false, suitable for assert(ldap_pvt_thread_rdwr_Xchk(rdwr))
234 * Currently they don't check if the calling thread is the one
235 * that has the lock, just that there is a reader or writer.
237 * Basically sufficent for testing that places that should have
241 int ldap_pvt_thread_rdwr_readers(ldap_pvt_thread_rdwr_t *rw)
243 assert( rw != NULL );
244 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
246 return( rw->ltrw_r_active );
249 int ldap_pvt_thread_rdwr_writers(ldap_pvt_thread_rdwr_t *rw)
251 assert( rw != NULL );
252 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
254 return( rw->ltrw_w_active );
257 int ldap_pvt_thread_rdwr_active(ldap_pvt_thread_rdwr_t *rw)
259 assert( rw != NULL );
260 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
262 return(ldap_pvt_thread_rdwr_readers(rw) +
263 ldap_pvt_thread_rdwr_writers(rw));
266 #endif /* LDAP_DEBUG */
268 #endif /* LDAP_THREAD_HAVE_RDWR */