/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
│ vi: set et ft=c ts=2 sts=2 sw=2 fenc=utf-8 :vi │
╞══════════════════════════════════════════════════════════════════════════════╡
│ Copyright 2022 Justine Alexandra Roberts Tunney │
│ │
│ Permission to use, copy, modify, and/or distribute this software for │
│ any purpose with or without fee is hereby granted, provided that the │
│ above copyright notice and this permission notice appear in all copies. │
│ │
│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL │
│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED │
│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE │
│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL │
│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR │
│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER │
│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR │
│ PERFORMANCE OF THIS SOFTWARE. │
╚─────────────────────────────────────────────────────────────────────────────*/
#include "libc/assert.h"
#include "libc/calls/blockcancel.internal.h"
#include "libc/calls/calls.h"
#include "libc/calls/struct/stat.h"
#include "libc/calls/syscall-sysv.internal.h"
#include "libc/dce.h"
#include "libc/errno.h"
#include "libc/intrin/atomic.h"
#include "libc/intrin/strace.internal.h"
#include "libc/limits.h"
#include "libc/mem/mem.h"
#include "libc/runtime/runtime.h"
#include "libc/runtime/syslib.internal.h"
#include "libc/str/str.h"
#include "libc/sysv/consts/at.h"
#include "libc/sysv/consts/map.h"
#include "libc/sysv/consts/o.h"
#include "libc/sysv/consts/prot.h"
#include "libc/sysv/errfuns.h"
#include "libc/thread/semaphore.h"
#include "libc/thread/thread.h"
#include "libc/thread/tls.h"
static struct Semaphores {
pthread_once_t once;
pthread_mutex_t lock;
struct Semaphore {
struct Semaphore *next;
sem_t *sem;
char *path;
bool dead;
int refs;
} * list;
} g_semaphores;
static void sem_open_lock(void) {
pthread_mutex_lock(&g_semaphores.lock);
}
static void sem_open_unlock(void) {
pthread_mutex_unlock(&g_semaphores.lock);
}
static void sem_open_wipe(void) {
pthread_mutex_init(&g_semaphores.lock, 0);
}
static void sem_open_setup(void) {
sem_open_wipe();
pthread_atfork(sem_open_lock, sem_open_unlock, sem_open_wipe);
}
static void sem_open_init(void) {
pthread_once(&g_semaphores.once, sem_open_setup);
}
static sem_t *sem_open_impl(const char *path, int oflag, unsigned mode,
unsigned value) {
int fd;
sem_t *sem;
struct stat st;
oflag |= O_RDWR | O_CLOEXEC;
if ((fd = openat(AT_FDCWD, path, oflag, mode)) == -1) {
return SEM_FAILED;
}
npassert(!fstat(fd, &st));
if (st.st_size < 4096 && ftruncate(fd, 4096) == -1) {
npassert(!close(fd));
return SEM_FAILED;
}
sem = mmap(0, 4096, PROT_READ | PROT_WRITE, MAP_SHARED, fd, 0);
if (sem != MAP_FAILED) {
atomic_store_explicit(&sem->sem_value, value, memory_order_relaxed);
sem->sem_magic = SEM_MAGIC_NAMED;
sem->sem_dev = st.st_dev;
sem->sem_ino = st.st_ino;
sem->sem_pshared = true;
} else {
sem = SEM_FAILED;
}
npassert(!close(fd));
return sem;
}
static struct Semaphore *sem_open_find(const char *path) {
struct Semaphore *s;
for (s = g_semaphores.list; s; s = s->next) {
if (!strcmp(path, s->path)) {
return s;
}
}
return 0;
}
static struct Semaphore *sem_open_reopen(const char *path) {
int e = errno;
struct stat st;
struct Semaphore *s;
for (s = g_semaphores.list; s; s = s->next) {
if (!s->dead && //
!strcmp(path, s->path)) {
if (!fstatat(AT_FDCWD, path, &st, 0) && //
st.st_dev == s->sem->sem_dev && //
st.st_ino == s->sem->sem_ino) {
return s;
} else {
errno = e;
s->dead = true;
}
}
}
return 0;
}
static struct Semaphore *sem_open_get(const sem_t *sem,
struct Semaphore ***out_prev) {
struct Semaphore *s, **p;
for (p = &g_semaphores.list, s = *p; s; p = &s->next, s = s->next) {
if (s && sem == s->sem) {
*out_prev = p;
return s;
}
}
return 0;
}
/**
* Initializes and opens named semaphore.
*
* This function tracks open semaphore objects within a process. When a
* process calls sem_open() multiple times with the same name, then the
* same shared memory address will be returned, unless it was unlinked.
*
* @param name is arbitrary string that begins with a slash character
* @param oflag can have any of:
* - `O_CREAT` to create the named semaphore if it doesn't exist,
* in which case two additional arguments must be supplied
* - `O_EXCL` to raise `EEXIST` if semaphore already exists
* @param mode is octal mode bits, required if `oflag & O_CREAT`
* @param value is initial of semaphore, required if `oflag & O_CREAT`
* @return semaphore object which needs sem_close(), or SEM_FAILED w/ errno
* @raise ENOSPC if file system is full when `name` would be `O_CREAT`ed
* @raise EINVAL if `oflag` has bits other than `O_CREAT | O_EXCL`
* @raise EINVAL if `value` is negative or exceeds `SEM_VALUE_MAX`
* @raise EEXIST if `O_CREAT|O_EXCL` is used and semaphore exists
* @raise EACCES if we didn't have permission to create semaphore
* @raise EACCES if recreating open semaphore pending an unlink
* @raise EMFILE if process `RLIMIT_NOFILE` has been reached
* @raise ENFILE if system-wide file limit has been reached
* @raise ENOMEM if we require more vespene gas
* @raise EINTR if signal handler was called
*/
sem_t *sem_open(const char *name, int oflag, ...) {
sem_t *sem;
va_list va;
char path[78];
struct Semaphore *s;
unsigned mode = 0, value = 0;
va_start(va, oflag);
mode = va_arg(va, unsigned);
value = va_arg(va, unsigned);
va_end(va);
#if 0
if (IsXnuSilicon()) {
long kernel;
if (!(sem = calloc(1, sizeof(sem_t)))) return SEM_FAILED;
sem->sem_magic = SEM_MAGIC_KERNEL;
kernel = _sysret(__syslib->__sem_open(name, oflag, mode, value));
if (kernel == -1) {
free(sem);
return SEM_FAILED;
}
sem->sem_magic = SEM_MAGIC_KERNEL;
sem->sem_kernel = (int *)kernel;
}
#endif
if (oflag & ~(O_CREAT | O_EXCL)) {
einval();
return SEM_FAILED;
}
if (oflag & O_CREAT) {
if (value > SEM_VALUE_MAX) {
einval();
return SEM_FAILED;
}
}
shm_path_np(name, path);
BLOCK_CANCELATION;
sem_open_init();
sem_open_lock();
if ((s = sem_open_reopen(path))) {
if (s->sem->sem_lazydelete) {
if (oflag & O_CREAT) {
eacces();
} else {
enoent();
}
sem = SEM_FAILED;
} else if (~oflag & O_EXCL) {
sem = s->sem;
atomic_fetch_add_explicit(&sem->sem_prefs, 1, memory_order_acq_rel);
++s->refs;
} else {
eexist();
sem = SEM_FAILED;
}
} else if ((s = calloc(1, sizeof(struct Semaphore)))) {
if ((s->path = strdup(path))) {
if ((sem = sem_open_impl(path, oflag, mode, value)) != SEM_FAILED) {
atomic_fetch_add_explicit(&sem->sem_prefs, 1, memory_order_acq_rel);
s->next = g_semaphores.list;
s->sem = sem;
s->refs = 1;
g_semaphores.list = s;
} else {
free(s->path);
free(s);
}
} else {
free(s);
sem = SEM_FAILED;
}
} else {
sem = SEM_FAILED;
}
sem_open_unlock();
ALLOW_CANCELATION;
return sem;
}
/**
* Closes named semaphore.
*
* Calling sem_close() on a semaphore not created by sem_open() has
* undefined behavior. Using `sem` after calling sem_close() from either
* the current process or forked processes sharing the same address is
* also undefined behavior. If any threads in this process or forked
* children are currently blocked on `sem` then calling sem_close() has
* undefined behavior.
*
* @param sem was created with sem_open()
* @return 0 on success, or -1 w/ errno
*/
int sem_close(sem_t *sem) {
int prefs;
bool unmap, delete;
struct Semaphore *s, **p;
#if 0
if (IsXnuSilicon()) {
npassert(sem->sem_magic == SEM_MAGIC_KERNEL);
return _sysret(__syslib->__sem_close(sem->sem_kernel));
}
#endif
npassert(sem->sem_magic == SEM_MAGIC_NAMED);
sem_open_init();
sem_open_lock();
npassert((s = sem_open_get(sem, &p)));
prefs = atomic_fetch_add_explicit(&sem->sem_prefs, -1, memory_order_acq_rel);
npassert(s->refs > 0);
if ((unmap = !--s->refs)) {
npassert(prefs > 0);
delete = sem->sem_lazydelete && prefs == 1;
*p = s->next;
} else {
npassert(prefs > 1);
delete = false;
}
sem_open_unlock();
if (unmap) {
npassert(!munmap(sem, 4096));
}
if (delete) {
unlink(s->path);
}
if (unmap) {
free(s->path);
free(s);
}
return 0;
}
/**
* Removes named semaphore.
*
* This causes the file resource to be deleted. If processes have this
* semaphore currently opened, then on platforms like Windows deletion
* may be postponed until the last process calls sem_close().
*
* @param name can be absolute path or should be component w/o slashes
* @return 0 on success, or -1 w/ errno
* @raise ACCESS if Windows is being fussy about deleting open files
* @raise EPERM if pledge() is in play w/o `cpath` promise
* @raise ENOENT if named semaphore doesn't exist
* @raise EACCES if permission is denied
* @raise ENAMETOOLONG if too long
*/
int sem_unlink(const char *name) {
char path[78];
int rc, e = errno;
struct Semaphore *s;
#if 0
if (IsXnuSilicon()) {
return _sysret(__syslib->__sem_unlink(name));
}
#endif
shm_path_np(name, path);
if ((rc = unlink(path)) == -1 && IsWindows() && errno == EACCES) {
sem_open_init();
sem_open_lock();
if ((s = sem_open_find(path))) {
s->sem->sem_lazydelete = true;
errno = e;
rc = 0;
}
sem_open_unlock();
}
return rc;
}