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 return LDAP_NO_MEMORY;
84 /* we should check return results */
85 ldap_pvt_thread_mutex_init( &rw->ltrw_mutex );
86 ldap_pvt_thread_cond_init( &rw->ltrw_read );
87 ldap_pvt_thread_cond_init( &rw->ltrw_write );
89 rw->ltrw_valid = LDAP_PVT_THREAD_RDWR_VALID;
96 ldap_pvt_thread_rdwr_destroy( ldap_pvt_thread_rdwr_t *rwlock )
98 struct ldap_int_thread_rdwr_s *rw;
100 assert( rwlock != NULL );
103 assert( rw != NULL );
104 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
106 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALID )
107 return LDAP_PVT_THREAD_EINVAL;
109 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
111 assert( rw->ltrw_w_active >= 0 );
112 assert( rw->ltrw_w_wait >= 0 );
113 assert( rw->ltrw_r_active >= 0 );
114 assert( rw->ltrw_r_wait >= 0 );
116 /* active threads? */
117 if( rw->ltrw_r_active > 0 || rw->ltrw_w_active > 0) {
118 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
119 return LDAP_PVT_THREAD_EBUSY;
122 /* waiting threads? */
123 if( rw->ltrw_r_wait > 0 || rw->ltrw_w_wait > 0) {
124 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
125 return LDAP_PVT_THREAD_EBUSY;
130 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
132 ldap_pvt_thread_mutex_destroy( &rw->ltrw_mutex );
133 ldap_pvt_thread_cond_destroy( &rw->ltrw_read );
134 ldap_pvt_thread_cond_destroy( &rw->ltrw_write );
141 int ldap_pvt_thread_rdwr_rlock( ldap_pvt_thread_rdwr_t *rwlock )
143 struct ldap_int_thread_rdwr_s *rw;
145 assert( rwlock != NULL );
148 assert( rw != NULL );
149 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
151 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALID )
152 return LDAP_PVT_THREAD_EINVAL;
154 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
156 assert( rw->ltrw_w_active >= 0 );
157 assert( rw->ltrw_w_wait >= 0 );
158 assert( rw->ltrw_r_active >= 0 );
159 assert( rw->ltrw_r_wait >= 0 );
161 if( rw->ltrw_w_active > 0 ) {
162 /* writer is active */
167 ldap_pvt_thread_cond_wait(
168 &rw->ltrw_read, &rw->ltrw_mutex );
169 } while( rw->ltrw_w_active > 0 );
172 assert( rw->ltrw_r_wait >= 0 );
175 #ifdef LDAP_RDWR_DEBUG
176 rw->ltrw_readers[rw->ltrw_r_active] = ldap_pvt_thread_self();
181 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
186 int ldap_pvt_thread_rdwr_rtrylock( ldap_pvt_thread_rdwr_t *rwlock )
188 struct ldap_int_thread_rdwr_s *rw;
190 assert( rwlock != NULL );
193 assert( rw != NULL );
194 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
196 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALID )
197 return LDAP_PVT_THREAD_EINVAL;
199 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
201 assert( rw->ltrw_w_active >= 0 );
202 assert( rw->ltrw_w_wait >= 0 );
203 assert( rw->ltrw_r_active >= 0 );
204 assert( rw->ltrw_r_wait >= 0 );
206 if( rw->ltrw_w_active > 0) {
207 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
208 return LDAP_PVT_THREAD_EBUSY;
211 #ifdef LDAP_RDWR_DEBUG
212 rw->ltrw_readers[rw->ltrw_r_active] = ldap_pvt_thread_self();
216 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
221 int ldap_pvt_thread_rdwr_runlock( ldap_pvt_thread_rdwr_t *rwlock )
223 struct ldap_int_thread_rdwr_s *rw;
225 assert( rwlock != NULL );
228 assert( rw != NULL );
229 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
231 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALID )
232 return LDAP_PVT_THREAD_EINVAL;
234 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
236 #ifdef LDAP_RDWR_DEBUG
237 /* Remove us from the list of readers */
239 ldap_pvt_thread_t self = ldap_pvt_thread_self();
241 for (i=0; i<rw->ltrw_r_active;i++)
243 if (rw->ltrw_readers[i] == self) {
244 for (j=i; j<rw->ltrw_r_active-1; j++)
245 rw->ltrw_readers[j] = rw->ltrw_readers[j+1];
246 rw->ltrw_readers[j] = 0;
254 assert( rw->ltrw_w_active >= 0 );
255 assert( rw->ltrw_w_wait >= 0 );
256 assert( rw->ltrw_r_active >= 0 );
257 assert( rw->ltrw_r_wait >= 0 );
259 if (rw->ltrw_r_active == 0 && rw->ltrw_w_wait > 0 ) {
260 ldap_pvt_thread_cond_signal( &rw->ltrw_write );
263 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
268 int ldap_pvt_thread_rdwr_wlock( ldap_pvt_thread_rdwr_t *rwlock )
270 struct ldap_int_thread_rdwr_s *rw;
272 assert( rwlock != NULL );
275 assert( rw != NULL );
276 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
278 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALID )
279 return LDAP_PVT_THREAD_EINVAL;
281 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
283 assert( rw->ltrw_w_active >= 0 );
284 assert( rw->ltrw_w_wait >= 0 );
285 assert( rw->ltrw_r_active >= 0 );
286 assert( rw->ltrw_r_wait >= 0 );
288 if ( rw->ltrw_w_active > 0 || rw->ltrw_r_active > 0 ) {
292 ldap_pvt_thread_cond_wait(
293 &rw->ltrw_write, &rw->ltrw_mutex );
294 } while ( rw->ltrw_w_active > 0 || rw->ltrw_r_active > 0 );
297 assert( rw->ltrw_w_wait >= 0 );
300 #ifdef LDAP_RDWR_DEBUG
301 rw->ltrw_writer = ldap_pvt_thread_self();
305 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
310 int ldap_pvt_thread_rdwr_wtrylock( 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 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALID )
321 return LDAP_PVT_THREAD_EINVAL;
323 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
325 assert( rw->ltrw_w_active >= 0 );
326 assert( rw->ltrw_w_wait >= 0 );
327 assert( rw->ltrw_r_active >= 0 );
328 assert( rw->ltrw_r_wait >= 0 );
330 if ( rw->ltrw_w_active > 0 || rw->ltrw_r_active > 0 ) {
331 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
332 return LDAP_PVT_THREAD_EBUSY;
335 #ifdef LDAP_RDWR_DEBUG
336 rw->ltrw_writer = ldap_pvt_thread_self();
340 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
345 int ldap_pvt_thread_rdwr_wunlock( ldap_pvt_thread_rdwr_t *rwlock )
347 struct ldap_int_thread_rdwr_s *rw;
349 assert( rwlock != NULL );
352 assert( rw != NULL );
353 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
355 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALID )
356 return LDAP_PVT_THREAD_EINVAL;
358 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
362 assert( rw->ltrw_w_active >= 0 );
363 assert( rw->ltrw_w_wait >= 0 );
364 assert( rw->ltrw_r_active >= 0 );
365 assert( rw->ltrw_r_wait >= 0 );
367 if (rw->ltrw_r_wait > 0) {
368 ldap_pvt_thread_cond_broadcast( &rw->ltrw_read );
370 } else if (rw->ltrw_w_wait > 0) {
371 ldap_pvt_thread_cond_signal( &rw->ltrw_write );
374 #ifdef LDAP_RDWR_DEBUG
377 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
382 #ifdef LDAP_RDWR_DEBUG
385 * return 0 if false, suitable for assert(ldap_pvt_thread_rdwr_Xchk(rdwr))
387 * Currently they don't check if the calling thread is the one
388 * that has the lock, just that there is a reader or writer.
390 * Basically sufficent for testing that places that should have
394 int ldap_pvt_thread_rdwr_readers(ldap_pvt_thread_rdwr_t *rwlock)
396 struct ldap_int_thread_rdwr_s *rw;
398 assert( rwlock != NULL );
401 assert( rw != NULL );
402 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
403 assert( rw->ltrw_w_active >= 0 );
404 assert( rw->ltrw_w_wait >= 0 );
405 assert( rw->ltrw_r_active >= 0 );
406 assert( rw->ltrw_r_wait >= 0 );
408 return( rw->ltrw_r_active );
411 int ldap_pvt_thread_rdwr_writers(ldap_pvt_thread_rdwr_t *rwlock)
413 struct ldap_int_thread_rdwr_s *rw;
415 assert( rwlock != NULL );
418 assert( rw != NULL );
419 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
420 assert( rw->ltrw_w_active >= 0 );
421 assert( rw->ltrw_w_wait >= 0 );
422 assert( rw->ltrw_r_active >= 0 );
423 assert( rw->ltrw_r_wait >= 0 );
425 return( rw->ltrw_w_active );
428 int ldap_pvt_thread_rdwr_active(ldap_pvt_thread_rdwr_t *rwlock)
430 struct ldap_int_thread_rdwr_s *rw;
432 assert( rwlock != NULL );
435 assert( rw != NULL );
436 assert( rw->ltrw_valid == LDAP_PVT_THREAD_RDWR_VALID );
437 assert( rw->ltrw_w_active >= 0 );
438 assert( rw->ltrw_w_wait >= 0 );
439 assert( rw->ltrw_r_active >= 0 );
440 assert( rw->ltrw_r_wait >= 0 );
442 return(ldap_pvt_thread_rdwr_readers(rwlock) +
443 ldap_pvt_thread_rdwr_writers(rwlock));
446 #endif /* LDAP_RDWR_DEBUG */
448 #endif /* LDAP_THREAD_HAVE_RDWR */