15 #include "fork_impl.h"
17 #define malloc __libc_malloc
18 #define calloc __libc_calloc
27 static volatile int lock[1];
28 volatile int *const __sem_open_lockptr = lock;
30 #define FLAGS (O_RDWR|O_NOFOLLOW|O_CLOEXEC|O_NONBLOCK)
32 sem_t *sem_open(const char *name, int flags, ...)
37 int fd, i, e, slot, first=1, cnt, cs;
43 char buf[NAME_MAX+10];
45 if (!(name = __shm_mapname(name, buf)))
49 /* Allocate table if we don't have one yet */
50 if (!semtab && !(semtab = calloc(sizeof *semtab, SEM_NSEMS_MAX))) {
55 /* Reserve a slot in case this semaphore is not mapped yet;
56 * this is necessary because there is no way to handle
57 * failures after creation of the file. */
59 for (cnt=i=0; i<SEM_NSEMS_MAX; i++) {
60 cnt += semtab[i].refcnt;
61 if (!semtab[i].sem && slot < 0) slot = i;
63 /* Avoid possibility of overflow later */
64 if (cnt == INT_MAX || slot < 0) {
69 /* Dummy pointer to make a reservation */
70 semtab[slot].sem = (sem_t *)-1;
73 flags &= (O_CREAT|O_EXCL);
75 pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &cs);
77 /* Early failure check for exclusive open; otherwise the case
78 * where the semaphore already exists is expensive. */
79 if (flags == (O_CREAT|O_EXCL) && access(name, F_OK) == 0) {
85 /* If exclusive mode is not requested, try opening an
86 * existing file first and fall back to creation. */
87 if (flags != (O_CREAT|O_EXCL)) {
88 fd = open(name, FLAGS);
90 if (fstat(fd, &st) < 0 ||
91 (map = mmap(0, sizeof(sem_t), PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0)) == MAP_FAILED) {
101 if (!(flags & O_CREAT))
106 mode = va_arg(ap, mode_t) & 0666;
107 value = va_arg(ap, unsigned);
109 if (value > SEM_VALUE_MAX) {
113 sem_init(&newsem, 1, value);
115 /* Create a temp file with the new semaphore contents
116 * and attempt to atomically link it as the new name */
117 clock_gettime(CLOCK_REALTIME, &ts);
118 snprintf(tmp, sizeof(tmp), "/dev/shm/tmp-%d", (int)ts.tv_nsec);
119 fd = open(tmp, O_CREAT|O_EXCL|FLAGS, mode);
121 if (errno == EEXIST) continue;
124 if (write(fd, &newsem, sizeof newsem) != sizeof newsem || fstat(fd, &st) < 0 ||
125 (map = mmap(0, sizeof(sem_t), PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0)) == MAP_FAILED) {
131 e = link(tmp, name) ? errno : 0;
134 munmap(map, sizeof(sem_t));
135 /* Failure is only fatal when doing an exclusive open;
136 * otherwise, next iteration will try to open the
138 if (e != EEXIST || flags == (O_CREAT|O_EXCL))
142 /* See if the newly mapped semaphore is already mapped. If
143 * so, unmap the new mapping and use the existing one. Otherwise,
144 * add it to the table of mapped semaphores. */
146 for (i=0; i<SEM_NSEMS_MAX && semtab[i].ino != st.st_ino; i++);
147 if (i<SEM_NSEMS_MAX) {
148 munmap(map, sizeof(sem_t));
149 semtab[slot].sem = 0;
153 semtab[slot].refcnt++;
154 semtab[slot].sem = map;
155 semtab[slot].ino = st.st_ino;
157 pthread_setcancelstate(cs, 0);
161 pthread_setcancelstate(cs, 0);
163 semtab[slot].sem = 0;
168 int sem_close(sem_t *sem)
172 for (i=0; i<SEM_NSEMS_MAX && semtab[i].sem != sem; i++);
173 if (--semtab[i].refcnt) {
180 munmap(sem, sizeof *sem);