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_unlock( &rw->ltrw_mutex );
65 ldap_pvt_thread_mutex_destroy( &rw->ltrw_mutex );
66 ldap_pvt_thread_cond_destroy( &rw->ltrw_read );
67 ldap_pvt_thread_cond_destroy( &rw->ltrw_write );
72 int ldap_pvt_thread_rdwr_rlock( ldap_pvt_thread_rdwr_t *rw )
74 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALUE )
75 return LDAP_PVT_THREAD_EINVAL;
77 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
79 if( rw->ltrw_w_active > 1 ) {
80 /* writer is active */
85 ldap_pvt_thread_cond_wait(
86 &rw->ltrw_read, &rw->ltrw_mutex );
87 } while( rw->ltrw_w_active > 1 );
94 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
99 int ldap_pvt_thread_rdwr_rtrylock( ldap_pvt_thread_rdwr_t *rw )
101 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALUE )
102 return LDAP_PVT_THREAD_EINVAL;
104 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
106 if( rw->ltrw_w_active > 1) {
107 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
108 return LDAP_PVT_THREAD_EBUSY;
113 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
118 int ldap_pvt_thread_rdwr_runlock( ldap_pvt_thread_rdwr_t *rw )
120 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALUE )
121 return LDAP_PVT_THREAD_EINVAL;
123 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
127 if (rw->ltrw_r_active == 0 && rw->ltrw_w_wait > 0 ) {
128 ldap_pvt_thread_cond_signal( &rw->ltrw_write );
131 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
136 int ldap_pvt_thread_rdwr_wlock( ldap_pvt_thread_rdwr_t *rw )
138 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALUE )
139 return LDAP_PVT_THREAD_EINVAL;
141 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
143 if ( rw->ltrw_w_active > 0 || rw->ltrw_r_active > 0 ) {
147 ldap_pvt_thread_cond_wait(
148 &rw->ltrw_write, &rw->ltrw_mutex );
149 } while ( rw->ltrw_w_active > 0 || rw->ltrw_r_active > 0 );
156 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
161 int ldap_pvt_thread_rdwr_wtrylock( ldap_pvt_thread_rdwr_t *rw )
163 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALUE )
164 return LDAP_PVT_THREAD_EINVAL;
166 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
168 if ( rw->ltrw_w_active > 0 || rw->ltrw_r_active > 0 ) {
169 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
170 return LDAP_PVT_THREAD_EBUSY;
175 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
180 int ldap_pvt_thread_rdwr_wunlock( ldap_pvt_thread_rdwr_t *rw )
182 if( rw->ltrw_valid != LDAP_PVT_THREAD_RDWR_VALUE )
183 return LDAP_PVT_THREAD_EINVAL;
185 ldap_pvt_thread_mutex_lock( &rw->ltrw_mutex );
189 if (rw->ltrw_r_wait > 0) {
190 ldap_pvt_thread_cond_broadcast( &rw->ltrw_read );
192 } else if (rw->ltrw_w_wait > 0) {
193 ldap_pvt_thread_cond_signal( &rw->ltrw_write );
196 ldap_pvt_thread_mutex_unlock( &rw->ltrw_mutex );
204 * return 0 if false, suitable for assert(ldap_pvt_thread_rdwr_Xchk(rdwr))
206 * Currently they don't check if the calling thread is the one
207 * that has the lock, just that there is a reader or writer.
209 * Basically sufficent for testing that places that should have
213 int ldap_pvt_thread_rdwr_readers(ldap_pvt_thread_rdwr_t *rw)
215 return( rw->ltrw_r_active );
218 int ldap_pvt_thread_rdwr_writers(ldap_pvt_thread_rdwr_t *rw)
220 return( rw->ltrw_w_active );
223 int ldap_pvt_thread_rdwr_active(ldap_pvt_thread_rdwr_t *rw)
225 return(ldap_pvt_thread_rdwr_readers(rw) +
226 ldap_pvt_thread_rdwr_writers(rw));
229 #endif /* LDAP_DEBUG */