package signal
Types of signals
The signals SIGKILL and SIGSTOP may not be caught by a program, and therefore cannot be affected by this package. //signal包捕捉不到这两个信号
Synchronous signals are signals triggered by errors in program execution: SIGBUS, SIGFPE, and SIGSEGV. These are only considered synchronous when caused by program execution, not when sent using os.Process.Kill or the kill program or some similar mechanism. In general, except as discussed below, Go programs will convert a synchronous signal into a run-time panic.
The remaining signals are asynchronous signals. They are not triggered by program errors, but are instead sent from the kernel or from some other program.
Of the asynchronous signals, the SIGHUP signal is sent when a program loses its controlling terminal. The SIGINT signal is sent when the user at the controlling terminal presses the interrupt character, which by default is ^C (Control-C). The SIGQUIT signal is sent when the user at the controlling terminal presses the quit character, which by default is ^ (Control-Backslash). In general you can cause a program to simply exit by pressing ^C, and you can cause it to exit with a stack dump(输出栈信息) by pressing ^.
Default behavior of signals in Go programs
By default, a synchronous signal is converted into a run-time panic. A SIGHUP, SIGINT, or SIGTERM signal causes the program to exit. A SIGQUIT, SIGILL, SIGTRAP, SIGABRT, SIGSTKFLT, SIGEMT, or SIGSYS signal causes the program to exit with a stack dump. A SIGTSTP, SIGTTIN, or SIGTTOU signal gets the system default behavior (these signals are used by the shell for job control). The SIGPROF signal is handled directly by the Go runtime to implement runtime.CPUProfile. Other signals will be caught but no action will be taken.
If the Go program is started with either SIGHUP or SIGINT ignored (signal handler set to SIG_IGN), they will remain ignored.
If the Go program is started with a non-empty signal mask, that will generally be honored. However, some signals are explicitly unblocked: the synchronous signals, SIGILL, SIGTRAP, SIGSTKFLT, SIGCHLD, SIGPROF, and, on GNU/Linux, signals 32 (SIGCANCEL) and 33 (SIGSETXID) (SIGCANCEL and SIGSETXID are used internally by glibc). Subprocesses started by os.Exec, or by the os/exec package, will inherit the modified signal mask.
Changing the behavior of signals in Go programs
The functions in this package allow a program to change the way Go programs handle signals.
Notify disables the default behavior for a given set of asynchronous signals and instead delivers them over one or more registered channels. Specifically, it applies to the signals SIGHUP, SIGINT, SIGQUIT, SIGABRT, and SIGTERM. It also applies to the job control signals SIGTSTP, SIGTTIN, and SIGTTOU, in which case the system default behavior does not occur. It also applies to some signals that otherwise cause no action: SIGUSR1, SIGUSR2, SIGPIPE, SIGALRM, SIGCHLD, SIGCONT, SIGURG, SIGXCPU, SIGXFSZ, SIGVTALRM, SIGWINCH, SIGIO, SIGPWR, SIGSYS, SIGINFO, SIGTHR, SIGWAITING, SIGLWP, SIGFREEZE, SIGTHAW, SIGLOST, SIGXRES, SIGJVM1, SIGJVM2, and any real time signals used on the system. Note that not all of these signals are available on all systems.
If the program was started with SIGHUP or SIGINT ignored, and Notify is called for either signal, a signal handler will be installed for that signal and it will no longer be ignored. If, later, Reset or Ignore is called for that signal, or Stop is called on all channels passed to Notify for that signal, the signal will once again be ignored. Reset will restore the system default behavior for the signal, while Ignore will cause the system to ignore the signal entirely.
If the program is started with a non-empty signal mask, some signals will be explicitly unblocked as described above. If Notify is called for a blocked signal, it will be unblocked. If, later, Reset is called for that signal, or Stop is called on all channels passed to Notify for that signal, the signal will once again be blocked.
func Ignore
Ignore causes the provided signals to be ignored. If they are received by the program, nothing will happen. Ignore undoes the effect of any prior calls to Notify for the provided signals. If no signals are provided, all incoming signals will be ignored.
func Notify
Notify causes package signal to relay incoming signals to c. If no signals are provided, all incoming signals will be relayed to c. Otherwise, just the provided signals will.
Package signal will not block sending to c: the caller must ensure that c has sufficient buffer space to keep up with the expected signal rate. For a channel used for notification of just one signal value, a buffer of size 1 is sufficient.
It is allowed to call Notify multiple times with the same channel: each call expands the set of signals sent to that channel. The only way to remove signals from the set is to call Stop.
It is allowed to call Notify multiple times with different channels and the same signals: each channel receives copies of incoming signals independently.
Code:play
// Set up channel on which to send signal notifications.
// We must use a buffered channel or risk missing the signal
// if we're not ready to receive when the signal is sent.
c := make(chan os.Signal, 1)
signal.Notify(c, os.Interrupt)
// Block until a signal is received.
s := <-c
fmt.Println("Got signal:", s)
func Reset
Reset undoes the effect of any prior calls to Notify for the provided signals. If no signals are provided, all signal handlers will be reset.
func Stop
Stop causes package signal to stop relaying incoming signals to c. It undoes the effect of all prior calls to Notify using c. When Stop returns, it is guaranteed that c will receive no more signals.
package main
import (
"fmt"
"os"
"os/signal"
"syscall"
"time"
)
func main() {
signalChan := make(chan os.Signal)
// 监听指定信号
signal.Notify(
signalChan,
syscall.SIGHUP,
syscall.SIGUSR2,
syscall.SIGKILL,
)
// 输出当前进程的pid
fmt.Println("pid is: ", os.Getpid())
go func() {
for {
time.Sleep(time.Second * 1)
signalChan <- nil
}
}()
// 处理信号
for {
sig := <-signalChan
fmt.Println("get signal: ", sig)
}
}