From: Ian Lance Taylor Date: Tue, 27 Jan 2026 04:03:30 +0000 (-0800) Subject: os/exec: document blocking Stdin/Stdout/Stderr X-Git-Url: http://www.git.cypherpunks.su/?a=commitdiff_plain;h=251f3aa6ee6fc3925fe8e64cd4b403bfa73b93ab;p=gostls13.git os/exec: document blocking Stdin/Stdout/Stderr WaitDelay only handles writes to Stdin and reads from Stdout/Stderr. If Stdin is set to a blocking Reader, or Stdout/Stderr are set to a blocking Writer, Wait can hang indefinitely. I don't see any way to fix this with the current API, as there is no general way that the os/exec package can interrupt the blocking Read or Write. This CL documents the limitation and points people toward the workaround of using StdinPipe/StdoutPipe/StderrPipe and arranging for their own way to interrupt the blocking Read or Write. Fixes #77227 Change-Id: I3150ae7af89dccf8d859b41eb43eaf0bbbb55fee Reviewed-on: https://go-review.googlesource.com/c/go/+/739422 Reviewed-by: Dmitri Shuralyov Auto-Submit: Ian Lance Taylor Reviewed-by: Sean Liao LUCI-TryBot-Result: Go LUCI Reviewed-by: Carlos Amedee --- diff --git a/src/os/exec/exec.go b/src/os/exec/exec.go index aa7a6be7f0..e5bf97a188 100644 --- a/src/os/exec/exec.go +++ b/src/os/exec/exec.go @@ -203,6 +203,11 @@ type Cmd struct { // stops copying, either because it has reached the end of Stdin // (EOF or a read error), or because writing to the pipe returned an error, // or because a nonzero WaitDelay was set and expired. + // + // Regardless of WaitDelay, Wait can block until a Read from + // Stdin completes. If you need to use a blocking io.Reader, + // use the StdinPipe method to get a pipe, copy from the Reader + // to the pipe, and arrange to close the Reader after Wait returns. Stdin io.Reader // Stdout and Stderr specify the process's standard output and error. @@ -219,6 +224,12 @@ type Cmd struct { // goroutine reaches EOF or encounters an error or a nonzero WaitDelay // expires. // + // Regardless of WaitDelay, Wait can block until a Write to + // Stdout or Stderr completes. If you need to use a blocking io.Writer, + // use the StdoutPipe or StderrPipe method to get a pipe, + // copy from the pipe to the Writer, and arrange to close the + // Writer after Wait returns. + // // If Stdout and Stderr are the same writer, and have a type that can // be compared with ==, at most one goroutine at a time will call Write. Stdout io.Writer