Current File : /home/vacivi36/vittasync.vacivitta.com.br/vittasync/node/deps/uv/src/unix/async.c
/* Copyright Joyent, Inc. and other Node contributors. All rights reserved.
* Permission is hereby granted, free of charge, to any person obtaining a copy
* of this software and associated documentation files (the "Software"), to
* deal in the Software without restriction, including without limitation the
* rights to use, copy, modify, merge, publish, distribute, sublicense, and/or
* sell copies of the Software, and to permit persons to whom the Software is
* furnished to do so, subject to the following conditions:
*
* The above copyright notice and this permission notice shall be included in
* all copies or substantial portions of the Software.
*
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
* FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
* IN THE SOFTWARE.
*/
/* This file contains both the uv__async internal infrastructure and the
* user-facing uv_async_t functions.
*/
#include "uv.h"
#include "internal.h"
#include <errno.h>
#include <stdatomic.h>
#include <stdio.h> /* snprintf() */
#include <assert.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
#include <sched.h> /* sched_yield() */
#ifdef __linux__
#include <sys/eventfd.h>
#endif
static void uv__async_send(uv_loop_t* loop);
static int uv__async_start(uv_loop_t* loop);
static void uv__cpu_relax(void);
int uv_async_init(uv_loop_t* loop, uv_async_t* handle, uv_async_cb async_cb) {
int err;
err = uv__async_start(loop);
if (err)
return err;
uv__handle_init(loop, (uv_handle_t*)handle, UV_ASYNC);
handle->async_cb = async_cb;
handle->pending = 0;
handle->u.fd = 0; /* This will be used as a busy flag. */
uv__queue_insert_tail(&loop->async_handles, &handle->queue);
uv__handle_start(handle);
return 0;
}
int uv_async_send(uv_async_t* handle) {
_Atomic int* pending;
_Atomic int* busy;
pending = (_Atomic int*) &handle->pending;
busy = (_Atomic int*) &handle->u.fd;
/* Do a cheap read first. */
if (atomic_load_explicit(pending, memory_order_relaxed) != 0)
return 0;
/* Set the loop to busy. */
atomic_fetch_add(busy, 1);
/* Wake up the other thread's event loop. */
if (atomic_exchange(pending, 1) == 0)
uv__async_send(handle->loop);
/* Set the loop to not-busy. */
atomic_fetch_add(busy, -1);
return 0;
}
/* Wait for the busy flag to clear before closing.
* Only call this from the event loop thread. */
static void uv__async_spin(uv_async_t* handle) {
_Atomic int* pending;
_Atomic int* busy;
int i;
pending = (_Atomic int*) &handle->pending;
busy = (_Atomic int*) &handle->u.fd;
/* Set the pending flag first, so no new events will be added by other
* threads after this function returns. */
atomic_store(pending, 1);
for (;;) {
/* 997 is not completely chosen at random. It's a prime number, acyclic by
* nature, and should therefore hopefully dampen sympathetic resonance.
*/
for (i = 0; i < 997; i++) {
if (atomic_load(busy) == 0)
return;
/* Other thread is busy with this handle, spin until it's done. */
uv__cpu_relax();
}
/* Yield the CPU. We may have preempted the other thread while it's
* inside the critical section and if it's running on the same CPU
* as us, we'll just burn CPU cycles until the end of our time slice.
*/
sched_yield();
}
}
void uv__async_close(uv_async_t* handle) {
uv__async_spin(handle);
uv__queue_remove(&handle->queue);
uv__handle_stop(handle);
}
static void uv__async_io(uv_loop_t* loop, uv__io_t* w, unsigned int events) {
char buf[1024];
ssize_t r;
struct uv__queue queue;
struct uv__queue* q;
uv_async_t* h;
_Atomic int *pending;
assert(w == &loop->async_io_watcher);
for (;;) {
r = read(w->fd, buf, sizeof(buf));
if (r == sizeof(buf))
continue;
if (r != -1)
break;
if (errno == EAGAIN || errno == EWOULDBLOCK)
break;
if (errno == EINTR)
continue;
abort();
}
uv__queue_move(&loop->async_handles, &queue);
while (!uv__queue_empty(&queue)) {
q = uv__queue_head(&queue);
h = uv__queue_data(q, uv_async_t, queue);
uv__queue_remove(q);
uv__queue_insert_tail(&loop->async_handles, q);
/* Atomically fetch and clear pending flag */
pending = (_Atomic int*) &h->pending;
if (atomic_exchange(pending, 0) == 0)
continue;
if (h->async_cb == NULL)
continue;
h->async_cb(h);
}
}
static void uv__async_send(uv_loop_t* loop) {
const void* buf;
ssize_t len;
int fd;
int r;
buf = "";
len = 1;
fd = loop->async_wfd;
#if defined(__linux__)
if (fd == -1) {
static const uint64_t val = 1;
buf = &val;
len = sizeof(val);
fd = loop->async_io_watcher.fd; /* eventfd */
}
#endif
do
r = write(fd, buf, len);
while (r == -1 && errno == EINTR);
if (r == len)
return;
if (r == -1)
if (errno == EAGAIN || errno == EWOULDBLOCK)
return;
abort();
}
static int uv__async_start(uv_loop_t* loop) {
int pipefd[2];
int err;
if (loop->async_io_watcher.fd != -1)
return 0;
#ifdef __linux__
err = eventfd(0, EFD_CLOEXEC | EFD_NONBLOCK);
if (err < 0)
return UV__ERR(errno);
pipefd[0] = err;
pipefd[1] = -1;
#else
err = uv__make_pipe(pipefd, UV_NONBLOCK_PIPE);
if (err < 0)
return err;
#endif
uv__io_init(&loop->async_io_watcher, uv__async_io, pipefd[0]);
uv__io_start(loop, &loop->async_io_watcher, POLLIN);
loop->async_wfd = pipefd[1];
return 0;
}
void uv__async_stop(uv_loop_t* loop) {
struct uv__queue queue;
struct uv__queue* q;
uv_async_t* h;
if (loop->async_io_watcher.fd == -1)
return;
/* Make sure no other thread is accessing the async handle fd after the loop
* cleanup.
*/
uv__queue_move(&loop->async_handles, &queue);
while (!uv__queue_empty(&queue)) {
q = uv__queue_head(&queue);
h = uv__queue_data(q, uv_async_t, queue);
uv__queue_remove(q);
uv__queue_insert_tail(&loop->async_handles, q);
uv__async_spin(h);
}
if (loop->async_wfd != -1) {
if (loop->async_wfd != loop->async_io_watcher.fd)
uv__close(loop->async_wfd);
loop->async_wfd = -1;
}
uv__io_stop(loop, &loop->async_io_watcher, POLLIN);
uv__close(loop->async_io_watcher.fd);
loop->async_io_watcher.fd = -1;
}
int uv__async_fork(uv_loop_t* loop) {
struct uv__queue queue;
struct uv__queue* q;
uv_async_t* h;
if (loop->async_io_watcher.fd == -1) /* never started */
return 0;
uv__queue_move(&loop->async_handles, &queue);
while (!uv__queue_empty(&queue)) {
q = uv__queue_head(&queue);
h = uv__queue_data(q, uv_async_t, queue);
uv__queue_remove(q);
uv__queue_insert_tail(&loop->async_handles, q);
/* The state of any thread that set pending is now likely corrupt in this
* child because the user called fork, so just clear these flags and move
* on. Calling most libc functions after `fork` is declared to be undefined
* behavior anyways, unless async-signal-safe, for multithreaded programs
* like libuv, and nothing interesting in pthreads is async-signal-safe.
*/
h->pending = 0;
/* This is the busy flag, and we just abruptly lost all other threads. */
h->u.fd = 0;
}
/* Recreate these, since they still exist, but belong to the wrong pid now. */
if (loop->async_wfd != -1) {
if (loop->async_wfd != loop->async_io_watcher.fd)
uv__close(loop->async_wfd);
loop->async_wfd = -1;
}
uv__io_stop(loop, &loop->async_io_watcher, POLLIN);
uv__close(loop->async_io_watcher.fd);
loop->async_io_watcher.fd = -1;
return uv__async_start(loop);
}
static void uv__cpu_relax(void) {
#if defined(__i386__) || defined(__x86_64__)
__asm__ __volatile__ ("rep; nop" ::: "memory"); /* a.k.a. PAUSE */
#elif (defined(__arm__) && __ARM_ARCH >= 7) || defined(__aarch64__)
__asm__ __volatile__ ("yield" ::: "memory");
#elif (defined(__ppc__) || defined(__ppc64__)) && defined(__APPLE__)
__asm volatile ("" : : : "memory");
#elif !defined(__APPLE__) && (defined(__powerpc64__) || defined(__ppc64__) || defined(__PPC64__))
__asm__ __volatile__ ("or 1,1,1; or 2,2,2" ::: "memory");
#endif
}
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