2 /* This work is part of OpenLDAP Software <http://www.openldap.org/>.
4 * Copyright 1998-2006 The OpenLDAP Foundation.
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted only as authorized by the OpenLDAP
11 * A copy of this license is available in file LICENSE in the
12 * top-level directory of the distribution or, alternatively, at
13 * <http://www.OpenLDAP.org/license.html>.
15 /* This work was initially developed by Kurt D. Zeilenga for inclusion
16 * in OpenLDAP Software. Additional significant contributors include:
21 * This is an improved implementation of Reader/Writer locks does
22 * not protect writers from starvation. That is, if a writer is
23 * currently waiting on a reader, any new reader will get
24 * the lock before the writer.
26 * Does not support cancellation nor does any status checking.
28 /* Adapted from publically available examples for:
29 * "Programming with Posix Threads"
30 * by David R Butenhof, Addison-Wesley
31 * http://cseng.aw.com/bookpage.taf?ISBN=0-201-63392-2
36 #include <ac/stdlib.h>
39 #include <ac/string.h>
43 #include "ldap_pvt_thread.h" /* Get the thread interface */
44 #define LDAP_THREAD_RDWR_IMPLEMENTATION
45 #include "ldap_thr_debug.h" /* May rename the symbols defined below */
48 * implementations that provide their own compatible
49 * reader/writer locks define LDAP_THREAD_HAVE_RDWR
50 * in ldap_pvt_thread.h
52 #ifndef LDAP_THREAD_HAVE_RDWR
54 struct ldap_int_thread_rdwr_s {
55 ldap_pvt_thread_mutex_t ltrw_mutex;
56 ldap_pvt_thread_cond_t ltrw_read; /* wait for read */
57 ldap_pvt_thread_cond_t ltrw_write; /* wait for write */
59 #define LDAP_PVT_THREAD_RDWR_VALID 0x0bad
64 #ifdef LDAP_RDWR_DEBUG
65 /* keep track of who has these locks */
66 #define MAX_READERS 32
67 ldap_pvt_thread_t ltrw_readers[MAX_READERS];
68 ldap_pvt_thread_t ltrw_writer;
73 ldap_pvt_thread_rdwr_init( ldap_pvt_thread_rdwr_t *rwlock )
75 struct ldap_int_thread_rdwr_s *rw;
77 assert( rwlock != NULL );
79 rw = (struct ldap_int_thread_rdwr_s *) LDAP_CALLOC( 1,
80 sizeof( struct ldap_int_thread_rdwr_s ) );
82 /* we should check return results */
83 ldap_pvt_thread_mutex_init( &rw->ltrw_mutex );
84 ldap_pvt_thread_cond_init( &rw->ltrw_read );
85 ldap_pvt_thread_cond_init( &rw->ltrw_write );
87 rw->ltrw_valid = LDAP_PVT_THREAD_RDWR_VALID;
94 ldap_pvt_thread_rdwr_destroy( ldap_pvt_thread_rdwr_t *rwlock )
96 struct ldap_int_thread_rdwr_s *rw;
98 assert( rwlock != NULL );
101 assert( rw != NULL );
102 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
104 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALID )
105 return LDAP_PVT_THREAD_EINVAL;
107 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
109 assert( rw->ltrw_w_active >= 0 );
110 assert( rw->ltrw_w_wait >= 0 );
111 assert( rw->ltrw_r_active >= 0 );
112 assert( rw->ltrw_r_wait >= 0 );
114 /* active threads? */
115 if( rw->ltrw_r_active > 0 || rw->ltrw_w_active > 0) {
116 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
117 return LDAP_PVT_THREAD_EBUSY;
120 /* waiting threads? */
121 if( rw->ltrw_r_wait > 0 || rw->ltrw_w_wait > 0) {
122 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
123 return LDAP_PVT_THREAD_EBUSY;
128 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
130 ldap_pvt_thread_mutex_destroy( &rw->ltrw_mutex );
131 ldap_pvt_thread_cond_destroy( &rw->ltrw_read );
132 ldap_pvt_thread_cond_destroy( &rw->ltrw_write );
139 int ldap_pvt_thread_rdwr_rlock( ldap_pvt_thread_rdwr_t *rwlock )
141 struct ldap_int_thread_rdwr_s *rw;
143 assert( rwlock != NULL );
146 assert( rw != NULL );
147 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
149 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALID )
150 return LDAP_PVT_THREAD_EINVAL;
152 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
154 assert( rw->ltrw_w_active >= 0 );
155 assert( rw->ltrw_w_wait >= 0 );
156 assert( rw->ltrw_r_active >= 0 );
157 assert( rw->ltrw_r_wait >= 0 );
159 if( rw->ltrw_w_active > 0 ) {
160 /* writer is active */
165 ldap_pvt_thread_cond_wait(
166 &rw->ltrw_read, &rw->ltrw_mutex );
167 } while( rw->ltrw_w_active > 0 );
170 assert( rw->ltrw_r_wait >= 0 );
173 #ifdef LDAP_RDWR_DEBUG
174 rw->ltrw_readers[rw->ltrw_r_active] = ldap_pvt_thread_self();
179 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
184 int ldap_pvt_thread_rdwr_rtrylock( ldap_pvt_thread_rdwr_t *rwlock )
186 struct ldap_int_thread_rdwr_s *rw;
188 assert( rwlock != NULL );
191 assert( rw != NULL );
192 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
194 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALID )
195 return LDAP_PVT_THREAD_EINVAL;
197 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
199 assert( rw->ltrw_w_active >= 0 );
200 assert( rw->ltrw_w_wait >= 0 );
201 assert( rw->ltrw_r_active >= 0 );
202 assert( rw->ltrw_r_wait >= 0 );
204 if( rw->ltrw_w_active > 0) {
205 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
206 return LDAP_PVT_THREAD_EBUSY;
209 #ifdef LDAP_RDWR_DEBUG
210 rw->ltrw_readers[rw->ltrw_r_active] = ldap_pvt_thread_self();
214 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
219 int ldap_pvt_thread_rdwr_runlock( ldap_pvt_thread_rdwr_t *rwlock )
221 struct ldap_int_thread_rdwr_s *rw;
223 assert( rwlock != NULL );
226 assert( rw != NULL );
227 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
229 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALID )
230 return LDAP_PVT_THREAD_EINVAL;
232 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
234 #ifdef LDAP_RDWR_DEBUG
235 /* Remove us from the list of readers */
237 ldap_pvt_thread_t self = ldap_pvt_thread_self();
239 for (i=0; i<rw->ltrw_r_active;i++)
241 if (rw->ltrw_readers[i] == self) {
242 for (j=i; j<rw->ltrw_r_active-1; j++)
243 rw->ltrw_readers[j] = rw->ltrw_readers[j+1];
244 rw->ltrw_readers[j] = 0;
252 assert( rw->ltrw_w_active >= 0 );
253 assert( rw->ltrw_w_wait >= 0 );
254 assert( rw->ltrw_r_active >= 0 );
255 assert( rw->ltrw_r_wait >= 0 );
257 if (rw->ltrw_r_active == 0 && rw->ltrw_w_wait > 0 ) {
258 ldap_pvt_thread_cond_signal( &rw->ltrw_write );
261 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
266 int ldap_pvt_thread_rdwr_wlock( ldap_pvt_thread_rdwr_t *rwlock )
268 struct ldap_int_thread_rdwr_s *rw;
270 assert( rwlock != NULL );
273 assert( rw != NULL );
274 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
276 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALID )
277 return LDAP_PVT_THREAD_EINVAL;
279 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
281 assert( rw->ltrw_w_active >= 0 );
282 assert( rw->ltrw_w_wait >= 0 );
283 assert( rw->ltrw_r_active >= 0 );
284 assert( rw->ltrw_r_wait >= 0 );
286 if ( rw->ltrw_w_active > 0 || rw->ltrw_r_active > 0 ) {
290 ldap_pvt_thread_cond_wait(
291 &rw->ltrw_write, &rw->ltrw_mutex );
292 } while ( rw->ltrw_w_active > 0 || rw->ltrw_r_active > 0 );
295 assert( rw->ltrw_w_wait >= 0 );
298 #ifdef LDAP_RDWR_DEBUG
299 rw->ltrw_writer = ldap_pvt_thread_self();
303 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
308 int ldap_pvt_thread_rdwr_wtrylock( ldap_pvt_thread_rdwr_t *rwlock )
310 struct ldap_int_thread_rdwr_s *rw;
312 assert( rwlock != NULL );
315 assert( rw != NULL );
316 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
318 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALID )
319 return LDAP_PVT_THREAD_EINVAL;
321 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
323 assert( rw->ltrw_w_active >= 0 );
324 assert( rw->ltrw_w_wait >= 0 );
325 assert( rw->ltrw_r_active >= 0 );
326 assert( rw->ltrw_r_wait >= 0 );
328 if ( rw->ltrw_w_active > 0 || rw->ltrw_r_active > 0 ) {
329 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
330 return LDAP_PVT_THREAD_EBUSY;
333 #ifdef LDAP_RDWR_DEBUG
334 rw->ltrw_writer = ldap_pvt_thread_self();
338 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
343 int ldap_pvt_thread_rdwr_wunlock( ldap_pvt_thread_rdwr_t *rwlock )
345 struct ldap_int_thread_rdwr_s *rw;
347 assert( rwlock != NULL );
350 assert( rw != NULL );
351 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
353 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALID )
354 return LDAP_PVT_THREAD_EINVAL;
356 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
360 assert( rw->ltrw_w_active >= 0 );
361 assert( rw->ltrw_w_wait >= 0 );
362 assert( rw->ltrw_r_active >= 0 );
363 assert( rw->ltrw_r_wait >= 0 );
365 if (rw->ltrw_r_wait > 0) {
366 ldap_pvt_thread_cond_broadcast( &rw->ltrw_read );
368 } else if (rw->ltrw_w_wait > 0) {
369 ldap_pvt_thread_cond_signal( &rw->ltrw_write );
372 #ifdef LDAP_RDWR_DEBUG
375 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
380 #ifdef LDAP_RDWR_DEBUG
383 * return 0 if false, suitable for assert(ldap_pvt_thread_rdwr_Xchk(rdwr))
385 * Currently they don't check if the calling thread is the one
386 * that has the lock, just that there is a reader or writer.
388 * Basically sufficent for testing that places that should have
392 int ldap_pvt_thread_rdwr_readers(ldap_pvt_thread_rdwr_t *rwlock)
394 struct ldap_int_thread_rdwr_s *rw;
396 assert( rwlock != NULL );
399 assert( rw != NULL );
400 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
401 assert( rw->ltrw_w_active >= 0 );
402 assert( rw->ltrw_w_wait >= 0 );
403 assert( rw->ltrw_r_active >= 0 );
404 assert( rw->ltrw_r_wait >= 0 );
406 return( rw->ltrw_r_active );
409 int ldap_pvt_thread_rdwr_writers(ldap_pvt_thread_rdwr_t *rwlock)
411 struct ldap_int_thread_rdwr_s *rw;
413 assert( rwlock != NULL );
416 assert( rw != NULL );
417 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
418 assert( rw->ltrw_w_active >= 0 );
419 assert( rw->ltrw_w_wait >= 0 );
420 assert( rw->ltrw_r_active >= 0 );
421 assert( rw->ltrw_r_wait >= 0 );
423 return( rw->ltrw_w_active );
426 int ldap_pvt_thread_rdwr_active(ldap_pvt_thread_rdwr_t *rwlock)
428 struct ldap_int_thread_rdwr_s *rw;
430 assert( rwlock != NULL );
433 assert( rw != NULL );
434 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
435 assert( rw->ltrw_w_active >= 0 );
436 assert( rw->ltrw_w_wait >= 0 );
437 assert( rw->ltrw_r_active >= 0 );
438 assert( rw->ltrw_r_wait >= 0 );
440 return(ldap_pvt_thread_rdwr_readers(rwlock) +
441 ldap_pvt_thread_rdwr_writers(rwlock));
444 #endif /* LDAP_RDWR_DEBUG */
446 #endif /* LDAP_THREAD_HAVE_RDWR */