diff options
Diffstat (limited to 'sysdeps/pthread/sem_routines.c')
| -rw-r--r-- | sysdeps/pthread/sem_routines.c | 187 |
1 files changed, 187 insertions, 0 deletions
diff --git a/sysdeps/pthread/sem_routines.c b/sysdeps/pthread/sem_routines.c new file mode 100644 index 0000000..78d9364 --- /dev/null +++ b/sysdeps/pthread/sem_routines.c @@ -0,0 +1,187 @@ +/* Helper code for POSIX semaphore implementation. + Copyright (C) 2021 Free Software Foundation, Inc. + This file is part of the GNU C Library. + + The GNU C Library is free software; you can redistribute it and/or + modify it under the terms of the GNU Lesser General Public + License as published by the Free Software Foundation; either + version 2.1 of the License, or (at your option) any later version. + + The GNU C Library is distributed in the hope that it will be useful, + but WITHOUT ANY WARRANTY; without even the implied warranty of + MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU + Lesser General Public License for more details. + + You should have received a copy of the GNU Lesser General Public + License along with the GNU C Library; if not, see + <https://www.gnu.org/licenses/>. */ + +#include <search.h> +#include <semaphoreP.h> +#include <sys/mman.h> +#include <sem_routines.h> + +/* Keeping track of currently used mappings. */ +struct inuse_sem +{ + dev_t dev; + ino_t ino; + int refcnt; + sem_t *sem; + char name[]; +}; + +/* Comparison function for search of existing mapping. */ +static int +sem_search (const void *a, const void *b) +{ + const struct inuse_sem *as = (const struct inuse_sem *) a; + const struct inuse_sem *bs = (const struct inuse_sem *) b; + + if (as->ino != bs->ino) + /* Cannot return the difference the type is larger than int. */ + return as->ino < bs->ino ? -1 : (as->ino == bs->ino ? 0 : 1); + + if (as->dev != bs->dev) + /* Cannot return the difference the type is larger than int. */ + return as->dev < bs->dev ? -1 : (as->dev == bs->dev ? 0 : 1); + + return strcmp (as->name, bs->name); +} + +/* The search tree for existing mappings. */ +static void *sem_mappings; + +/* Lock to protect the search tree. */ +static int sem_mappings_lock = LLL_LOCK_INITIALIZER; + + +/* Search for existing mapping and if possible add the one provided. */ +sem_t * +__sem_check_add_mapping (const char *name, int fd, sem_t *existing) +{ + size_t namelen = strlen (name); + sem_t *result = SEM_FAILED; + + /* Get the information about the file. */ + struct stat64 st; + if (__fstat64 (fd, &st) == 0) + { + /* Get the lock. */ + lll_lock (sem_mappings_lock, LLL_PRIVATE); + + /* Search for an existing mapping given the information we have. */ + struct inuse_sem *fake; + fake = (struct inuse_sem *) alloca (sizeof (*fake) + namelen); + memcpy (fake->name, name, namelen); + fake->dev = st.st_dev; + fake->ino = st.st_ino; + + struct inuse_sem **foundp = __tfind (fake, &sem_mappings, sem_search); + if (foundp != NULL) + { + /* There is already a mapping. Use it. */ + result = (*foundp)->sem; + ++(*foundp)->refcnt; + } + else + { + /* We haven't found a mapping. Install ione. */ + struct inuse_sem *newp; + + newp = (struct inuse_sem *) malloc (sizeof (*newp) + namelen); + if (newp != NULL) + { + /* If the caller hasn't provided any map it now. */ + if (existing == SEM_FAILED) + existing = (sem_t *) mmap (NULL, sizeof (sem_t), + PROT_READ | PROT_WRITE, MAP_SHARED, + fd, 0); + + newp->dev = st.st_dev; + newp->ino = st.st_ino; + newp->refcnt = 1; + newp->sem = existing; + memcpy (newp->name, name, namelen); + + /* Insert the new value. */ + if (existing != MAP_FAILED + && __tsearch (newp, &sem_mappings, sem_search) != NULL) + /* Successful. */ + result = existing; + else + /* Something went wrong while inserting the new + value. We fail completely. */ + free (newp); + } + } + + /* Release the lock. */ + lll_unlock (sem_mappings_lock, LLL_PRIVATE); + } + + if (result != existing && existing != SEM_FAILED && existing != MAP_FAILED) + { + /* Do not disturb errno. */ + int save = errno; + munmap (existing, sizeof (sem_t)); + errno = save; + } + + return result; +} + +struct walk_closure +{ + sem_t *the_sem; + struct inuse_sem *rec; +}; + +static void +walker (const void *inodep, VISIT which, void *closure0) +{ + struct walk_closure *closure = closure0; + struct inuse_sem *nodep = *(struct inuse_sem **) inodep; + + if (nodep->sem == closure->the_sem) + closure->rec = nodep; +} + +bool +__sem_remove_mapping (sem_t *sem) +{ + bool ret = true; + + /* Get the lock. */ + lll_lock (sem_mappings_lock, LLL_PRIVATE); + + /* Locate the entry for the mapping the caller provided. */ + struct inuse_sem *rec; + { + struct walk_closure closure = { .the_sem = sem, .rec = NULL }; + __twalk_r (sem_mappings, walker, &closure); + rec = closure.rec; + } + if (rec != NULL) + { + /* Check the reference counter. If it is going to be zero, free + all the resources. */ + if (--rec->refcnt == 0) + { + /* Remove the record from the tree. */ + __tdelete (rec, &sem_mappings, sem_search); + + if (munmap (rec->sem, sizeof (sem_t)) == -1) + ret = false; + + free (rec); + } + } + else + ret = false; + + /* Release the lock. */ + lll_unlock (sem_mappings_lock, LLL_PRIVATE); + + return ret; +} |