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>
25 #include "ldap_pvt_thread.h"
28 * implementations that provide their own compatible
29 * reader/writer locks define LDAP_THREAD_HAVE_RDWR
30 * in ldap_pvt_thread.h
32 #ifndef LDAP_THREAD_HAVE_RDWR
34 struct ldap_int_thread_rdwr_s {
35 ldap_pvt_thread_mutex_t ltrw_mutex;
36 ldap_pvt_thread_cond_t ltrw_read; /* wait for read */
37 ldap_pvt_thread_cond_t ltrw_write; /* wait for write */
39 #define LDAP_PVT_THREAD_RDWR_VALID 0x0bad
47 ldap_pvt_thread_rdwr_init( ldap_pvt_thread_rdwr_t *rwlock )
49 struct ldap_int_thread_rdwr_s *rw;
51 assert( rwlock != NULL );
53 rw = (struct ldap_int_thread_rdwr_s *) LDAP_CALLOC( 1,
54 sizeof( struct ldap_int_thread_rdwr_s ) );
56 /* we should check return results */
57 ldap_pvt_thread_mutex_init( &rw->ltrw_mutex );
58 ldap_pvt_thread_cond_init( &rw->ltrw_read );
59 ldap_pvt_thread_cond_init( &rw->ltrw_write );
61 rw->ltrw_valid = LDAP_PVT_THREAD_RDWR_VALID;
68 ldap_pvt_thread_rdwr_destroy( ldap_pvt_thread_rdwr_t *rwlock )
70 struct ldap_int_thread_rdwr_s *rw;
72 assert( rwlock != NULL );
76 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
78 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALID )
79 return LDAP_PVT_THREAD_EINVAL;
81 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
84 if( rw->ltrw_r_active > 0 || rw->ltrw_w_active > 0) {
85 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
86 return LDAP_PVT_THREAD_EBUSY;
89 /* waiting threads? */
90 if( rw->ltrw_r_wait > 0 || rw->ltrw_w_wait > 0) {
91 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
92 return LDAP_PVT_THREAD_EBUSY;
97 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
99 ldap_pvt_thread_mutex_destroy( &rw->ltrw_mutex );
100 ldap_pvt_thread_cond_destroy( &rw->ltrw_read );
101 ldap_pvt_thread_cond_destroy( &rw->ltrw_write );
108 int ldap_pvt_thread_rdwr_rlock( ldap_pvt_thread_rdwr_t *rwlock )
110 struct ldap_int_thread_rdwr_s *rw;
112 assert( rwlock != NULL );
115 assert( rw != NULL );
116 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
118 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALID )
119 return LDAP_PVT_THREAD_EINVAL;
121 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
123 if( rw->ltrw_w_active > 0 ) {
124 /* writer is active */
129 ldap_pvt_thread_cond_wait(
130 &rw->ltrw_read, &rw->ltrw_mutex );
131 } while( rw->ltrw_w_active > 0 );
138 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
143 int ldap_pvt_thread_rdwr_rtrylock( ldap_pvt_thread_rdwr_t *rwlock )
145 struct ldap_int_thread_rdwr_s *rw;
147 assert( rwlock != NULL );
150 assert( rw != NULL );
151 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
153 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALID )
154 return LDAP_PVT_THREAD_EINVAL;
156 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
158 if( rw->ltrw_w_active > 0) {
159 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
160 return LDAP_PVT_THREAD_EBUSY;
165 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
170 int ldap_pvt_thread_rdwr_runlock( ldap_pvt_thread_rdwr_t *rwlock )
172 struct ldap_int_thread_rdwr_s *rw;
174 assert( rwlock != NULL );
177 assert( rw != NULL );
178 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
180 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALID )
181 return LDAP_PVT_THREAD_EINVAL;
183 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
187 if (rw->ltrw_r_active == 0 && rw->ltrw_w_wait > 0 ) {
188 ldap_pvt_thread_cond_signal( &rw->ltrw_write );
191 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
196 int ldap_pvt_thread_rdwr_wlock( ldap_pvt_thread_rdwr_t *rwlock )
198 struct ldap_int_thread_rdwr_s *rw;
200 assert( rwlock != NULL );
203 assert( rw != NULL );
204 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
206 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALID )
207 return LDAP_PVT_THREAD_EINVAL;
209 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
211 if ( rw->ltrw_w_active > 0 || rw->ltrw_r_active > 0 ) {
215 ldap_pvt_thread_cond_wait(
216 &rw->ltrw_write, &rw->ltrw_mutex );
217 } while ( rw->ltrw_w_active > 0 || rw->ltrw_r_active > 0 );
224 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
229 int ldap_pvt_thread_rdwr_wtrylock( ldap_pvt_thread_rdwr_t *rwlock )
231 struct ldap_int_thread_rdwr_s *rw;
233 assert( rwlock != NULL );
236 assert( rw != NULL );
237 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
239 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALID )
240 return LDAP_PVT_THREAD_EINVAL;
242 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
244 if ( rw->ltrw_w_active > 0 || rw->ltrw_r_active > 0 ) {
245 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
246 return LDAP_PVT_THREAD_EBUSY;
251 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
256 int ldap_pvt_thread_rdwr_wunlock( ldap_pvt_thread_rdwr_t *rwlock )
258 struct ldap_int_thread_rdwr_s *rw;
260 assert( rwlock != NULL );
263 assert( rw != NULL );
264 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
266 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALID )
267 return LDAP_PVT_THREAD_EINVAL;
269 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
273 if (rw->ltrw_r_wait > 0) {
274 ldap_pvt_thread_cond_broadcast( &rw->ltrw_read );
276 } else if (rw->ltrw_w_wait > 0) {
277 ldap_pvt_thread_cond_signal( &rw->ltrw_write );
280 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
285 #ifdef LDAP_RDWR_DEBUG
288 * return 0 if false, suitable for assert(ldap_pvt_thread_rdwr_Xchk(rdwr))
290 * Currently they don't check if the calling thread is the one
291 * that has the lock, just that there is a reader or writer.
293 * Basically sufficent for testing that places that should have
297 int ldap_pvt_thread_rdwr_readers(ldap_pvt_thread_rdwr_t *rwlock)
299 struct ldap_int_thread_rdwr_s *rw;
301 assert( rwlock != NULL );
304 assert( rw != NULL );
305 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
307 return( rw->ltrw_r_active );
310 int ldap_pvt_thread_rdwr_writers(ldap_pvt_thread_rdwr_t *rwlock)
312 struct ldap_int_thread_rdwr_s *rw;
314 assert( rwlock != NULL );
317 assert( rw != NULL );
318 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
320 return( rw->ltrw_w_active );
323 int ldap_pvt_thread_rdwr_active(ldap_pvt_thread_rdwr_t *rwlock)
325 struct ldap_int_thread_rdwr_s *rw;
327 assert( rwlock != NULL );
330 assert( rw != NULL );
331 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
333 return(ldap_pvt_thread_rdwr_readers(rw) +
334 ldap_pvt_thread_rdwr_writers(rw));
337 #endif /* LDAP_DEBUG */
339 #endif /* LDAP_THREAD_HAVE_RDWR */