main: synchronize writes to VT100-faker on Windows
We use a third-party library "colorable" to translate VT100 color sequences into Windows console attribute-setting calls when Terraform is running on Windows. colorable is not concurrency-safe for multiple writes to the same console, because it writes to the console one character at a time and so two concurrent writers get their characters interleaved, creating unreadable garble. Here we wrap around it a synchronization mechanism to ensure that there can be only one Write call outstanding across both stderr and stdout, mimicking the usual behavior we expect (when stderr/stdout are a normal file handle) of each Write being completed atomically.
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9
main.go
9
main.go
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@ -258,6 +258,15 @@ func copyOutput(r io.Reader, doneCh chan<- struct{}) {
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if runtime.GOOS == "windows" {
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if runtime.GOOS == "windows" {
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stdout = colorable.NewColorableStdout()
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stdout = colorable.NewColorableStdout()
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stderr = colorable.NewColorableStderr()
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stderr = colorable.NewColorableStderr()
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// colorable is not concurrency-safe when stdout and stderr are the
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// same console, so we need to add some synchronization to ensure that
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// we can't be concurrently writing to both stderr and stdout at
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// once, or else we get intermingled writes that create gibberish
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// in the console.
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wrapped := synchronizedWriters(stdout, stderr)
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stdout = wrapped[0]
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stderr = wrapped[1]
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}
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}
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var wg sync.WaitGroup
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var wg sync.WaitGroup
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@ -0,0 +1,31 @@
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package main
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import (
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"io"
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"sync"
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)
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type synchronizedWriter struct {
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io.Writer
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mutex *sync.Mutex
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}
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// synchronizedWriters takes a set of writers and returns wrappers that ensure
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// that only one write can be outstanding at a time across the whole set.
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func synchronizedWriters(targets ...io.Writer) []io.Writer {
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mutex := &sync.Mutex{}
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ret := make([]io.Writer, len(targets))
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for i, target := range targets {
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ret[i] = &synchronizedWriter{
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Writer: target,
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mutex: mutex,
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}
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}
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return ret
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}
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func (w *synchronizedWriter) Write(p []byte) (int, error) {
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w.mutex.Lock()
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defer w.mutex.Unlock()
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return w.Writer.Write(p)
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}
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