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 ********************************************************
23 #include <ac/string.h>
25 #include "ldap_pvt_thread.h"
28 ldap_pvt_thread_rdwr_init( ldap_pvt_thread_rdwr_t *rw )
30 memset( rw, 0, sizeof(ldap_pvt_thread_rdwr_t) );
32 /* we should check return results */
33 ldap_pvt_thread_mutex_init( &rw->ltrw_mutex );
34 ldap_pvt_thread_cond_init( &rw->ltrw_read );
35 ldap_pvt_thread_cond_init( &rw->ltrw_write );
37 rw->ltrw_valid = LDAP_PVT_THREAD_RDWR_VALUE;
42 ldap_pvt_thread_rdwr_destroy( ldap_pvt_thread_rdwr_t *rw )
44 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALUE )
45 return LDAP_PVT_THREAD_EINVAL;
47 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
50 if( rw->ltrw_r_active > 0 || rw->ltrw_w_active > 1) {
51 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
52 return LDAP_PVT_THREAD_EBUSY;
55 /* waiting threads? */
56 if( rw->ltrw_r_wait > 0 || rw->ltrw_w_wait > 0) {
57 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
58 return LDAP_PVT_THREAD_EBUSY;
64 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
66 ldap_pvt_thread_mutex_destroy( &rw->ltrw_mutex );
67 ldap_pvt_thread_cond_destroy( &rw->ltrw_read );
68 ldap_pvt_thread_cond_destroy( &rw->ltrw_write );
73 int ldap_pvt_thread_rdwr_rlock( ldap_pvt_thread_rdwr_t *rw )
75 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALUE )
76 return LDAP_PVT_THREAD_EINVAL;
78 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
80 if( rw->ltrw_w_active > 1 ) {
81 /* writer is active */
86 ldap_pvt_thread_cond_wait(
87 &rw->ltrw_read, &rw->ltrw_mutex );
88 } while( rw->ltrw_w_active > 1 );
95 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
100 int ldap_pvt_thread_rdwr_rtrylock( ldap_pvt_thread_rdwr_t *rw )
102 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALUE )
103 return LDAP_PVT_THREAD_EINVAL;
105 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
107 if( rw->ltrw_w_active > 1) {
108 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
109 return LDAP_PVT_THREAD_EBUSY;
114 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
119 int ldap_pvt_thread_rdwr_runlock( ldap_pvt_thread_rdwr_t *rw )
121 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALUE )
122 return LDAP_PVT_THREAD_EINVAL;
124 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
128 if (rw->ltrw_r_active == 0 && rw->ltrw_w_wait > 0 ) {
129 ldap_pvt_thread_cond_signal( &rw->ltrw_write );
132 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
137 int ldap_pvt_thread_rdwr_wlock( ldap_pvt_thread_rdwr_t *rw )
139 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALUE )
140 return LDAP_PVT_THREAD_EINVAL;
142 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
144 if ( rw->ltrw_w_active > 0 || rw->ltrw_r_active > 0 ) {
148 ldap_pvt_thread_cond_wait(
149 &rw->ltrw_write, &rw->ltrw_mutex );
150 } while ( rw->ltrw_w_active > 0 || rw->ltrw_r_active > 0 );
157 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
162 int ldap_pvt_thread_rdwr_wtrylock( ldap_pvt_thread_rdwr_t *rw )
164 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALUE )
165 return LDAP_PVT_THREAD_EINVAL;
167 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
169 if ( rw->ltrw_w_active > 0 || rw->ltrw_r_active > 0 ) {
170 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
171 return LDAP_PVT_THREAD_EBUSY;
176 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
181 int ldap_pvt_thread_rdwr_wunlock( ldap_pvt_thread_rdwr_t *rw )
183 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALUE )
184 return LDAP_PVT_THREAD_EINVAL;
186 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
190 if (rw->ltrw_r_wait > 0) {
191 ldap_pvt_thread_cond_broadcast( &rw->ltrw_read );
193 } else if (rw->ltrw_w_wait > 0) {
194 ldap_pvt_thread_cond_signal( &rw->ltrw_write );
197 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
205 * return 0 if false, suitable for assert(ldap_pvt_thread_rdwr_Xchk(rdwr))
207 * Currently they don't check if the calling thread is the one
208 * that has the lock, just that there is a reader or writer.
210 * Basically sufficent for testing that places that should have
214 int ldap_pvt_thread_rdwr_readers(ldap_pvt_thread_rdwr_t *rw)
216 return( rw->ltrw_r_active );
219 int ldap_pvt_thread_rdwr_writers(ldap_pvt_thread_rdwr_t *rw)
221 return( rw->ltrw_w_active );
224 int ldap_pvt_thread_rdwr_active(ldap_pvt_thread_rdwr_t *rw)
226 return(ldap_pvt_thread_rdwr_readers(rw) +
227 ldap_pvt_thread_rdwr_writers(rw));
230 #endif /* LDAP_DEBUG */