knative.dev/pkg@v0.0.0-20260602142205-ac97e43f6622/signals/signal.go (about)

     1  /*
     2  Copyright 2018 The Knative Authors
     3  
     4  Licensed under the Apache License, Version 2.0 (the "License");
     5  you may not use this file except in compliance with the License.
     6  You may obtain a copy of the License at
     7  
     8      http://www.apache.org/licenses/LICENSE-2.0
     9  
    10  Unless required by applicable law or agreed to in writing, software
    11  distributed under the License is distributed on an "AS IS" BASIS,
    12  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    13  See the License for the specific language governing permissions and
    14  limitations under the License.
    15  */
    16  
    17  package signals
    18  
    19  import (
    20  	"context"
    21  	"os"
    22  	"os/signal"
    23  	"time"
    24  )
    25  
    26  var onlyOneSignalHandler = make(chan struct{})
    27  
    28  // SetupSignalHandler registered for SIGTERM and SIGINT. A stop channel is returned
    29  // which is closed on one of these signals. If a second signal is caught, the program
    30  // is terminated with exit code 1.
    31  func SetupSignalHandler() (stopCh <-chan struct{}) {
    32  	close(onlyOneSignalHandler) // panics when called twice
    33  
    34  	stop := make(chan struct{})
    35  	c := make(chan os.Signal, 2)
    36  	signal.Notify(c, shutdownSignals...)
    37  	go func() {
    38  		<-c
    39  		close(stop)
    40  		<-c
    41  		os.Exit(1) // second signal. Exit directly.
    42  	}()
    43  
    44  	return stop
    45  }
    46  
    47  // NewContext creates a new context with SetupSignalHandler()
    48  // as our Done() channel.
    49  func NewContext() context.Context {
    50  	return &signalContext{stopCh: SetupSignalHandler()}
    51  }
    52  
    53  type signalContext struct {
    54  	stopCh <-chan struct{}
    55  }
    56  
    57  // Deadline implements context.Context
    58  func (scc *signalContext) Deadline() (deadline time.Time, ok bool) {
    59  	return deadline, ok
    60  }
    61  
    62  // Done implements context.Context
    63  func (scc *signalContext) Done() <-chan struct{} {
    64  	return scc.stopCh
    65  }
    66  
    67  // Err implements context.Context. If the underlying stop channel is closed, Err
    68  // always returns context.Canceled, and nil otherwise.
    69  func (scc *signalContext) Err() error {
    70  	select {
    71  	case _, ok := <-scc.Done():
    72  		if !ok {
    73  			// TODO: revisit this behavior when Deadline() implementation is changed
    74  			return context.Canceled
    75  		}
    76  	default:
    77  	}
    78  	return nil
    79  }
    80  
    81  // Value implements context.Context
    82  func (scc *signalContext) Value(key interface{}) interface{} {
    83  	return nil
    84  }