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;
63 ldap_pvt_thread_mutex_destroy( &rw->ltrw_mutex );
64 ldap_pvt_thread_cond_destroy( &rw->ltrw_read );
65 ldap_pvt_thread_cond_destroy( &rw->ltrw_write );
70 int ldap_pvt_thread_rdwr_rlock( ldap_pvt_thread_rdwr_t *rw )
72 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALUE )
73 return LDAP_PVT_THREAD_EINVAL;
75 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
77 if( rw->ltrw_w_active > 1 ) {
78 /* writer is active */
83 ldap_pvt_thread_cond_wait(
84 &rw->ltrw_read, &rw->ltrw_mutex );
85 } while( rw->ltrw_w_active > 1 );
92 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
97 int ldap_pvt_thread_rdwr_rtrylock( ldap_pvt_thread_rdwr_t *rw )
99 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALUE )
100 return LDAP_PVT_THREAD_EINVAL;
102 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
104 if( rw->ltrw_w_active > 1) {
105 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
106 return LDAP_PVT_THREAD_EBUSY;
111 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
116 int ldap_pvt_thread_rdwr_runlock( ldap_pvt_thread_rdwr_t *rw )
118 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALUE )
119 return LDAP_PVT_THREAD_EINVAL;
121 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
125 if (rw->ltrw_r_active == 0 && rw->ltrw_w_wait > 0 ) {
126 ldap_pvt_thread_cond_signal( &rw->ltrw_write );
129 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
134 int ldap_pvt_thread_rdwr_wlock( ldap_pvt_thread_rdwr_t *rw )
136 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALUE )
137 return LDAP_PVT_THREAD_EINVAL;
139 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
141 if ( rw->ltrw_w_active > 0 || rw->ltrw_r_active > 0 ) {
145 ldap_pvt_thread_cond_wait(
146 &rw->ltrw_write, &rw->ltrw_mutex );
147 } while ( rw->ltrw_w_active > 0 || rw->ltrw_r_active > 0 );
154 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
159 int ldap_pvt_thread_rdwr_wtrylock( ldap_pvt_thread_rdwr_t *rw )
161 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALUE )
162 return LDAP_PVT_THREAD_EINVAL;
164 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
166 if ( rw->ltrw_w_active > 0 || rw->ltrw_r_active > 0 ) {
167 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
168 return LDAP_PVT_THREAD_EBUSY;
173 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
178 int ldap_pvt_thread_rdwr_wunlock( ldap_pvt_thread_rdwr_t *rw )
180 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALUE )
181 return LDAP_PVT_THREAD_EINVAL;
183 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
187 if (rw->ltrw_r_wait > 0) {
188 ldap_pvt_thread_cond_broadcast( &rw->ltrw_read );
190 } else if (rw->ltrw_w_wait > 0) {
191 ldap_pvt_thread_cond_signal( &rw->ltrw_write );
194 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
202 * return 0 if false, suitable for assert(ldap_pvt_thread_rdwr_Xchk(rdwr))
204 * Currently they don't check if the calling thread is the one
205 * that has the lock, just that there is a reader or writer.
207 * Basically sufficent for testing that places that should have
211 int ldap_pvt_thread_rdwr_readers(ldap_pvt_thread_rdwr_t *rw)
213 return( rw->ltrw_r_active );
216 int ldap_pvt_thread_rdwr_writers(ldap_pvt_thread_rdwr_t *rw)
218 return( rw->ltrw_w_active );
221 int ldap_pvt_thread_rdwr_active(ldap_pvt_thread_rdwr_t *rw)
223 return(ldap_pvt_thread_rdwr_readers(rw) +
224 ldap_pvt_thread_rdwr_writers(rw));
227 #endif /* LDAP_DEBUG */