Merge pull request #429 from go-kit/log-docs
Enhance package log docs.
Chris Hines authored 6 years ago
GitHub committed 6 years ago
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// handled atomically within the wrapped logger, but it typically serializes
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// both the formatting and output logic. Use a SyncLogger if the formatting
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// logger may perform multiple writes per log event.
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//
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// Error Handling
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//
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// This package relies on the practice of wrapping or decorating loggers with
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// other loggers to provide composable pieces of functionality. It also means
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// that Logger.Log must return an error because some
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// implementations—especially those that output log data to an io.Writer—may
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// encounter errors that cannot be handled locally. This in turn means that
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// Loggers that wrap other loggers should return errors from the wrapped
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// logger up the stack.
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//
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// Fortunately, the decorator pattern also provides a way to avoid the
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// necessity to check for errors every time an application calls Logger.Log.
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// An application required to panic whenever its Logger encounters
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// an error could initialize its logger as follows.
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//
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// fmtlogger := log.NewLogfmtLogger(log.NewSyncWriter(os.Stdout))
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// logger := log.LoggerFunc(func(keyvals ...interface{}) error {
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// if err := fmtlogger.Log(keyvals...); err != nil {
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// panic(err)
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// }
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// return nil
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// })
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package log
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package log_test
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import (
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"math/rand"
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"os"
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"sync"
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"time"
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"github.com/go-kit/kit/log"
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logger.Log("call", "third")
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// Output:
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// time=2015-02-03T10:00:01Z caller=example_test.go:91 call=first
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// time=2015-02-03T10:00:02Z caller=example_test.go:92 call=second
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// time=2015-02-03T10:00:03Z caller=example_test.go:96 call=third
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// time=2015-02-03T10:00:01Z caller=example_test.go:93 call=first
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// time=2015-02-03T10:00:02Z caller=example_test.go:94 call=second
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// time=2015-02-03T10:00:03Z caller=example_test.go:98 call=third
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}
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func Example_syncWriter() {
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w := log.NewSyncWriter(os.Stdout)
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logger := log.NewLogfmtLogger(w)
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type Task struct {
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ID int
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}
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var wg sync.WaitGroup
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RunTask := func(task Task, logger log.Logger) {
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logger.Log("taskID", task.ID, "event", "starting task")
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time.Sleep(time.Duration(rand.Intn(200)) * time.Millisecond)
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logger.Log("taskID", task.ID, "event", "task complete")
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wg.Done()
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}
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wg.Add(2)
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go RunTask(Task{ID: 1}, logger)
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go RunTask(Task{ID: 2}, logger)
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wg.Wait()
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// Unordered output:
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// taskID=1 event="starting task"
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// taskID=2 event="starting task"
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// taskID=1 event="task complete"
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// taskID=2 event="task complete"
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}
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