2 /* This work is part of OpenLDAP Software <http://www.openldap.org/>.
4 * Copyright 1998-2005 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"
46 * implementations that provide their own compatible
47 * reader/writer locks define LDAP_THREAD_HAVE_RDWR
48 * in ldap_pvt_thread.h
50 #ifndef LDAP_THREAD_HAVE_RDWR
52 struct ldap_int_thread_rdwr_s {
53 ldap_pvt_thread_mutex_t ltrw_mutex;
54 ldap_pvt_thread_cond_t ltrw_read; /* wait for read */
55 ldap_pvt_thread_cond_t ltrw_write; /* wait for write */
57 #define LDAP_PVT_THREAD_RDWR_VALID 0x0bad
62 #ifdef LDAP_RDWR_DEBUG
63 /* keep track of who has these locks */
64 #define MAX_READERS 32
65 ldap_pvt_thread_t ltrw_readers[MAX_READERS];
66 ldap_pvt_thread_t ltrw_writer;
71 ldap_pvt_thread_rdwr_init( ldap_pvt_thread_rdwr_t *rwlock )
73 struct ldap_int_thread_rdwr_s *rw;
75 assert( rwlock != NULL );
77 rw = (struct ldap_int_thread_rdwr_s *) LDAP_CALLOC( 1,
78 sizeof( struct ldap_int_thread_rdwr_s ) );
80 /* we should check return results */
81 ldap_pvt_thread_mutex_init( &rw->ltrw_mutex );
82 ldap_pvt_thread_cond_init( &rw->ltrw_read );
83 ldap_pvt_thread_cond_init( &rw->ltrw_write );
85 rw->ltrw_valid = LDAP_PVT_THREAD_RDWR_VALID;
92 ldap_pvt_thread_rdwr_destroy( ldap_pvt_thread_rdwr_t *rwlock )
94 struct ldap_int_thread_rdwr_s *rw;
96 assert( rwlock != NULL );
100 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
102 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALID )
103 return LDAP_PVT_THREAD_EINVAL;
105 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
107 assert( rw->ltrw_w_active >= 0 );
108 assert( rw->ltrw_w_wait >= 0 );
109 assert( rw->ltrw_r_active >= 0 );
110 assert( rw->ltrw_r_wait >= 0 );
112 /* active threads? */
113 if( rw->ltrw_r_active > 0 || rw->ltrw_w_active > 0) {
114 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
115 return LDAP_PVT_THREAD_EBUSY;
118 /* waiting threads? */
119 if( rw->ltrw_r_wait > 0 || rw->ltrw_w_wait > 0) {
120 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
121 return LDAP_PVT_THREAD_EBUSY;
126 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
128 ldap_pvt_thread_mutex_destroy( &rw->ltrw_mutex );
129 ldap_pvt_thread_cond_destroy( &rw->ltrw_read );
130 ldap_pvt_thread_cond_destroy( &rw->ltrw_write );
137 int ldap_pvt_thread_rdwr_rlock( ldap_pvt_thread_rdwr_t *rwlock )
139 struct ldap_int_thread_rdwr_s *rw;
141 assert( rwlock != NULL );
144 assert( rw != NULL );
145 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
147 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALID )
148 return LDAP_PVT_THREAD_EINVAL;
150 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
152 assert( rw->ltrw_w_active >= 0 );
153 assert( rw->ltrw_w_wait >= 0 );
154 assert( rw->ltrw_r_active >= 0 );
155 assert( rw->ltrw_r_wait >= 0 );
157 if( rw->ltrw_w_active > 0 ) {
158 /* writer is active */
163 ldap_pvt_thread_cond_wait(
164 &rw->ltrw_read, &rw->ltrw_mutex );
165 } while( rw->ltrw_w_active > 0 );
168 assert( rw->ltrw_r_wait >= 0 );
171 #ifdef LDAP_RDWR_DEBUG
172 rw->ltrw_readers[rw->ltrw_r_active] = ldap_pvt_thread_self();
177 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
182 int ldap_pvt_thread_rdwr_rtrylock( ldap_pvt_thread_rdwr_t *rwlock )
184 struct ldap_int_thread_rdwr_s *rw;
186 assert( rwlock != NULL );
189 assert( rw != NULL );
190 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
192 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALID )
193 return LDAP_PVT_THREAD_EINVAL;
195 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
197 assert( rw->ltrw_w_active >= 0 );
198 assert( rw->ltrw_w_wait >= 0 );
199 assert( rw->ltrw_r_active >= 0 );
200 assert( rw->ltrw_r_wait >= 0 );
202 if( rw->ltrw_w_active > 0) {
203 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
204 return LDAP_PVT_THREAD_EBUSY;
207 #ifdef LDAP_RDWR_DEBUG
208 rw->ltrw_readers[rw->ltrw_r_active] = ldap_pvt_thread_self();
212 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
217 int ldap_pvt_thread_rdwr_runlock( ldap_pvt_thread_rdwr_t *rwlock )
219 struct ldap_int_thread_rdwr_s *rw;
221 assert( rwlock != NULL );
224 assert( rw != NULL );
225 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
227 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALID )
228 return LDAP_PVT_THREAD_EINVAL;
230 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
232 #ifdef LDAP_RDWR_DEBUG
233 /* Remove us from the list of readers */
235 ldap_pvt_thread_t self = ldap_pvt_thread_self();
237 for (i=0; i<rw->ltrw_r_active;i++)
239 if (rw->ltrw_readers[i] == self) {
240 for (j=i; j<rw->ltrw_r_active-1; j++)
241 rw->ltrw_readers[j] = rw->ltrw_readers[j+1];
242 rw->ltrw_readers[j] = 0;
250 assert( rw->ltrw_w_active >= 0 );
251 assert( rw->ltrw_w_wait >= 0 );
252 assert( rw->ltrw_r_active >= 0 );
253 assert( rw->ltrw_r_wait >= 0 );
255 if (rw->ltrw_r_active == 0 && rw->ltrw_w_wait > 0 ) {
256 ldap_pvt_thread_cond_signal( &rw->ltrw_write );
259 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
264 int ldap_pvt_thread_rdwr_wlock( ldap_pvt_thread_rdwr_t *rwlock )
266 struct ldap_int_thread_rdwr_s *rw;
268 assert( rwlock != NULL );
271 assert( rw != NULL );
272 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
274 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALID )
275 return LDAP_PVT_THREAD_EINVAL;
277 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
279 assert( rw->ltrw_w_active >= 0 );
280 assert( rw->ltrw_w_wait >= 0 );
281 assert( rw->ltrw_r_active >= 0 );
282 assert( rw->ltrw_r_wait >= 0 );
284 if ( rw->ltrw_w_active > 0 || rw->ltrw_r_active > 0 ) {
288 ldap_pvt_thread_cond_wait(
289 &rw->ltrw_write, &rw->ltrw_mutex );
290 } while ( rw->ltrw_w_active > 0 || rw->ltrw_r_active > 0 );
293 assert( rw->ltrw_w_wait >= 0 );
296 #ifdef LDAP_RDWR_DEBUG
297 rw->ltrw_writer = ldap_pvt_thread_self();
301 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
306 int ldap_pvt_thread_rdwr_wtrylock( ldap_pvt_thread_rdwr_t *rwlock )
308 struct ldap_int_thread_rdwr_s *rw;
310 assert( rwlock != NULL );
313 assert( rw != NULL );
314 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
316 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALID )
317 return LDAP_PVT_THREAD_EINVAL;
319 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
321 assert( rw->ltrw_w_active >= 0 );
322 assert( rw->ltrw_w_wait >= 0 );
323 assert( rw->ltrw_r_active >= 0 );
324 assert( rw->ltrw_r_wait >= 0 );
326 if ( rw->ltrw_w_active > 0 || rw->ltrw_r_active > 0 ) {
327 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
328 return LDAP_PVT_THREAD_EBUSY;
331 #ifdef LDAP_RDWR_DEBUG
332 rw->ltrw_writer = ldap_pvt_thread_self();
336 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
341 int ldap_pvt_thread_rdwr_wunlock( ldap_pvt_thread_rdwr_t *rwlock )
343 struct ldap_int_thread_rdwr_s *rw;
345 assert( rwlock != NULL );
348 assert( rw != NULL );
349 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
351 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALID )
352 return LDAP_PVT_THREAD_EINVAL;
354 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
358 assert( rw->ltrw_w_active >= 0 );
359 assert( rw->ltrw_w_wait >= 0 );
360 assert( rw->ltrw_r_active >= 0 );
361 assert( rw->ltrw_r_wait >= 0 );
363 if (rw->ltrw_r_wait > 0) {
364 ldap_pvt_thread_cond_broadcast( &rw->ltrw_read );
366 } else if (rw->ltrw_w_wait > 0) {
367 ldap_pvt_thread_cond_signal( &rw->ltrw_write );
370 #ifdef LDAP_RDWR_DEBUG
373 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
378 #ifdef LDAP_RDWR_DEBUG
381 * return 0 if false, suitable for assert(ldap_pvt_thread_rdwr_Xchk(rdwr))
383 * Currently they don't check if the calling thread is the one
384 * that has the lock, just that there is a reader or writer.
386 * Basically sufficent for testing that places that should have
390 int ldap_pvt_thread_rdwr_readers(ldap_pvt_thread_rdwr_t *rwlock)
392 struct ldap_int_thread_rdwr_s *rw;
394 assert( rwlock != NULL );
397 assert( rw != NULL );
398 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
399 assert( rw->ltrw_w_active >= 0 );
400 assert( rw->ltrw_w_wait >= 0 );
401 assert( rw->ltrw_r_active >= 0 );
402 assert( rw->ltrw_r_wait >= 0 );
404 return( rw->ltrw_r_active );
407 int ldap_pvt_thread_rdwr_writers(ldap_pvt_thread_rdwr_t *rwlock)
409 struct ldap_int_thread_rdwr_s *rw;
411 assert( rwlock != NULL );
414 assert( rw != NULL );
415 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
416 assert( rw->ltrw_w_active >= 0 );
417 assert( rw->ltrw_w_wait >= 0 );
418 assert( rw->ltrw_r_active >= 0 );
419 assert( rw->ltrw_r_wait >= 0 );
421 return( rw->ltrw_w_active );
424 int ldap_pvt_thread_rdwr_active(ldap_pvt_thread_rdwr_t *rwlock)
426 struct ldap_int_thread_rdwr_s *rw;
428 assert( rwlock != NULL );
431 assert( rw != NULL );
432 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
433 assert( rw->ltrw_w_active >= 0 );
434 assert( rw->ltrw_w_wait >= 0 );
435 assert( rw->ltrw_r_active >= 0 );
436 assert( rw->ltrw_r_wait >= 0 );
438 return(ldap_pvt_thread_rdwr_readers(rwlock) +
439 ldap_pvt_thread_rdwr_writers(rwlock));
442 #endif /* LDAP_DEBUG */
444 #endif /* LDAP_THREAD_HAVE_RDWR */