2 ** This is an improved implementation of Reader/Writer locks does
3 ** not protect writers from starvation. That is, if a writer is
4 ** currently waiting on a reader, any new reader will get
5 ** the lock before the writer.
7 ** Does not support cancellation nor does any status checking.
10 /********************************************************
12 * "Programming with Posix Threads"
15 ********************************************************
20 #include <ac/stdlib.h>
23 #include <ac/string.h>
25 #include "ldap_pvt_thread.h"
28 ldap_pvt_thread_rdwr_init( ldap_pvt_thread_rdwr_t *rw )
32 memset( rw, 0, sizeof(ldap_pvt_thread_rdwr_t) );
34 /* we should check return results */
35 ldap_pvt_thread_mutex_init( &rw->ltrw_mutex );
36 ldap_pvt_thread_cond_init( &rw->ltrw_read );
37 ldap_pvt_thread_cond_init( &rw->ltrw_write );
39 rw->ltrw_valid = LDAP_PVT_THREAD_RDWR_VALID;
44 ldap_pvt_thread_rdwr_destroy( ldap_pvt_thread_rdwr_t *rw )
47 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
49 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALID )
50 return LDAP_PVT_THREAD_EINVAL;
52 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
55 if( rw->ltrw_r_active > 0 || rw->ltrw_w_active > 1) {
56 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
57 return LDAP_PVT_THREAD_EBUSY;
60 /* waiting threads? */
61 if( rw->ltrw_r_wait > 0 || rw->ltrw_w_wait > 0) {
62 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
63 return LDAP_PVT_THREAD_EBUSY;
68 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
70 ldap_pvt_thread_mutex_destroy( &rw->ltrw_mutex );
71 ldap_pvt_thread_cond_destroy( &rw->ltrw_read );
72 ldap_pvt_thread_cond_destroy( &rw->ltrw_write );
77 int ldap_pvt_thread_rdwr_rlock( ldap_pvt_thread_rdwr_t *rw )
80 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
82 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALID )
83 return LDAP_PVT_THREAD_EINVAL;
85 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
87 if( rw->ltrw_w_active > 1 ) {
88 /* writer is active */
93 ldap_pvt_thread_cond_wait(
94 &rw->ltrw_read, &rw->ltrw_mutex );
95 } while( rw->ltrw_w_active > 1 );
102 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
107 int ldap_pvt_thread_rdwr_rtrylock( ldap_pvt_thread_rdwr_t *rw )
109 assert( rw != NULL );
110 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
112 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALID )
113 return LDAP_PVT_THREAD_EINVAL;
115 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
117 if( rw->ltrw_w_active > 1) {
118 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
119 return LDAP_PVT_THREAD_EBUSY;
124 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
129 int ldap_pvt_thread_rdwr_runlock( ldap_pvt_thread_rdwr_t *rw )
131 assert( rw != NULL );
132 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
134 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALID )
135 return LDAP_PVT_THREAD_EINVAL;
137 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
141 if (rw->ltrw_r_active == 0 && rw->ltrw_w_wait > 0 ) {
142 ldap_pvt_thread_cond_signal( &rw->ltrw_write );
145 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
150 int ldap_pvt_thread_rdwr_wlock( ldap_pvt_thread_rdwr_t *rw )
152 assert( rw != NULL );
153 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
155 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALID )
156 return LDAP_PVT_THREAD_EINVAL;
158 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
160 if ( rw->ltrw_w_active > 0 || rw->ltrw_r_active > 0 ) {
164 ldap_pvt_thread_cond_wait(
165 &rw->ltrw_write, &rw->ltrw_mutex );
166 } while ( rw->ltrw_w_active > 0 || rw->ltrw_r_active > 0 );
173 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
178 int ldap_pvt_thread_rdwr_wtrylock( ldap_pvt_thread_rdwr_t *rw )
180 assert( rw != NULL );
181 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
183 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALID )
184 return LDAP_PVT_THREAD_EINVAL;
186 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
188 if ( rw->ltrw_w_active > 0 || rw->ltrw_r_active > 0 ) {
189 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
190 return LDAP_PVT_THREAD_EBUSY;
195 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
200 int ldap_pvt_thread_rdwr_wunlock( ldap_pvt_thread_rdwr_t *rw )
202 assert( rw != NULL );
203 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
205 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALID )
206 return LDAP_PVT_THREAD_EINVAL;
208 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
212 if (rw->ltrw_r_wait > 0) {
213 ldap_pvt_thread_cond_broadcast( &rw->ltrw_read );
215 } else if (rw->ltrw_w_wait > 0) {
216 ldap_pvt_thread_cond_signal( &rw->ltrw_write );
219 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
227 * return 0 if false, suitable for assert(ldap_pvt_thread_rdwr_Xchk(rdwr))
229 * Currently they don't check if the calling thread is the one
230 * that has the lock, just that there is a reader or writer.
232 * Basically sufficent for testing that places that should have
236 int ldap_pvt_thread_rdwr_readers(ldap_pvt_thread_rdwr_t *rw)
238 assert( rw != NULL );
239 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
241 return( rw->ltrw_r_active );
244 int ldap_pvt_thread_rdwr_writers(ldap_pvt_thread_rdwr_t *rw)
246 assert( rw != NULL );
247 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
249 return( rw->ltrw_w_active );
252 int ldap_pvt_thread_rdwr_active(ldap_pvt_thread_rdwr_t *rw)
254 assert( rw != NULL );
255 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
257 return(ldap_pvt_thread_rdwr_readers(rw) +
258 ldap_pvt_thread_rdwr_writers(rw));
261 #endif /* LDAP_DEBUG */