cmd/go: disable SSH connection pooling to avoid git hang

Fixes #13453.
Fixes #16104.

Change-Id: I4e94f606df786af8143f8649c9afde570f346301
Reviewed-on: https://go-review.googlesource.com/31353
Reviewed-by: Quentin Smith <quentin@golang.org>

diff --git a/src/cmd/go/get.go b/src/cmd/go/get.go
index 01b4e015d2929523a277bee177b0335d729c4d52..4f7562b43db21900effbd73c09e8e91c989eb4f6 100644 (file)
--- a/src/cmd/go/get.go
+++ b/src/cmd/go/get.go
@@ -98,6 +98,23 @@ func runGet(cmd *Command, args []string) {
                os.Setenv("GIT_TERMINAL_PROMPT", "0")
        }
 
+       // Disable any ssh connection pooling by Git.
+       // If a Git subprocess forks a child into the background to cache a new connection,
+       // that child keeps stdout/stderr open. After the Git subprocess exits,
+       // os /exec expects to be able to read from the stdout/stderr pipe
+       // until EOF to get all the data that the Git subprocess wrote before exiting.
+       // The EOF doesn't come until the child exits too, because the child
+       // is holding the write end of the pipe.
+       // This is unfortunate, but it has come up at least twice
+       // (see golang.org/issue/13453 and golang.org/issue/16104)
+       // and confuses users when it does.
+       // If the user has explicitly set GIT_SSH or GIT_SSH_COMMAND,
+       // assume they know what they are doing and don't step on it.
+       // But default to turning off ControlMaster.
+       if os.Getenv("GIT_SSH") == "" && os.Getenv("GIT_SSH_COMMAND") == "" {
+               os.Setenv("GIT_SSH_COMMAND", "ssh -o ControlMaster=no")
+       }
+
        // Phase 1.  Download/update.
        var stk importStack
        mode := 0