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structured logging: replacing Fatal/Exit/etc. without loss of flushing
When structured logging called for functions like Fatal and Exit to be avoided in favor of klog.ErrorS + os.Exit, it was overlooked that this replacement skips flushing. We could ask developers to use klog.ErrorS + klog.Flush + os.Exit, but that is still not quite the same because klog.Flush could get stuck or take too long. Therefore klog now supports flushing + exiting with a dedicated function that can be combined with some other, arbitrary logging function.
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// Go support for leveled logs, analogous to https://code.google.com/p/google-glog/ | ||
// | ||
// Copyright 2013 Google Inc. All Rights Reserved. | ||
// | ||
// Licensed under the Apache License, Version 2.0 (the "License"); | ||
// you may not use this file except in compliance with the License. | ||
// You may obtain a copy of the License at | ||
// | ||
// http://www.apache.org/licenses/LICENSE-2.0 | ||
// | ||
// Unless required by applicable law or agreed to in writing, software | ||
// distributed under the License is distributed on an "AS IS" BASIS, | ||
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
// See the License for the specific language governing permissions and | ||
// limitations under the License. | ||
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package klog | ||
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import ( | ||
"fmt" | ||
"os" | ||
"time" | ||
) | ||
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var ( | ||
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// ExitFlushTimeout is the timeout that klog has traditionally used during | ||
// calls like Fatal or Exit when flushing log data right before exiting. | ||
// Applications that replace those calls and do not have some specific | ||
// requirements like "exit immediately" can use this value as parameter | ||
// for FlushAndExit. | ||
ExitFlushTimeout = 10 * time.Second | ||
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// OsExit is the function called by FlushAndExit to terminate the program. | ||
OsExit = os.Exit | ||
) | ||
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// FlushAndExit flushes log data for a certain amount of time and then calls | ||
// os.Exit. Combined with some logging call it provides a replacement for | ||
// traditional calls like Fatal or Exit. | ||
func FlushAndExit(flushTimeout time.Duration, exitCode int) { | ||
timeoutFlush(flushTimeout) | ||
OsExit(exitCode) | ||
} | ||
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// timeoutFlush calls Flush and returns when it completes or after timeout | ||
// elapses, whichever happens first. This is needed because the hooks invoked | ||
// by Flush may deadlock when klog.Fatal is called from a hook that holds | ||
// a lock. Flushing also might take too long. | ||
func timeoutFlush(timeout time.Duration) { | ||
done := make(chan bool, 1) | ||
go func() { | ||
Flush() // calls logging.lockAndFlushAll() | ||
done <- true | ||
}() | ||
select { | ||
case <-done: | ||
case <-time.After(timeout): | ||
fmt.Fprintln(os.Stderr, "klog: Flush took longer than", timeout) | ||
} | ||
} |
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// Copyright 2020 The Kubernetes Authors. | ||
// | ||
// Licensed under the Apache License, Version 2.0 (the "License"); | ||
// you may not use this file except in compliance with the License. | ||
// You may obtain a copy of the License at | ||
// | ||
// http://www.apache.org/licenses/LICENSE-2.0 | ||
// | ||
// Unless required by applicable law or agreed to in writing, software | ||
// distributed under the License is distributed on an "AS IS" BASIS, | ||
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. | ||
// See the License for the specific language governing permissions and | ||
// limitations under the License. | ||
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package klog_test | ||
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import ( | ||
"flag" | ||
"fmt" | ||
"os" | ||
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"k8s.io/klog/v2" | ||
) | ||
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func ExampleFlushAndExit() { | ||
// Set up klog so that we can test it below. | ||
var fs flag.FlagSet | ||
klog.InitFlags(&fs) | ||
fs.Set("skip_headers", "true") | ||
defer flag.Set("skip_headers", "false") | ||
klog.SetOutput(os.Stdout) | ||
defer klog.SetOutput(nil) | ||
klog.OsExit = func(exitCode int) { | ||
fmt.Printf("os.Exit(%d)\n", exitCode) | ||
} | ||
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// If we were to return or exit without flushing, this message would | ||
// get lost because it is buffered in memory by klog when writing to | ||
// files. Output to stderr is not buffered. | ||
klog.InfoS("exiting...") | ||
exitCode := 10 | ||
klog.FlushAndExit(klog.ExitFlushTimeout, exitCode) | ||
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// Output: | ||
// "exiting..." | ||
// os.Exit(10) | ||
} |
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