os: EINTR on Darwin when reading from os.Stdin

[tibbes]

What did you do?

I built this program on a Mac, and also cross-compiled it using GOOS=linux, then ran it on both platforms to see what happened when I hit Ctrl-Z and resumed the program using fg 1.

package main

import (
        "bufio"
        "fmt"
        "os"
)

func main() {
        scanner := bufio.NewScanner(os.Stdin)
        for scanner.Scan() {
        }
        fmt.Println(scanner.Err())
}

What did you see on Linux?

$ ./tmp
^Z
[1]+  Stopped                 ./tmp
$ fg 1
./tmp

What did you see on Darwin (macOS)?

$ ./tmp
^Z
[1]+  Stopped                 ./tmp
$ fg 1
./tmp
read /dev/stdin: interrupted system call
$

What would you expect?

I would expect the behaviour to be the same on both platforms. A search of other issues indicated that the following may be relevant:

• os: OpenFile may return EINTR on OS X #11180 / https://golang.org/cl/14484 (fixed the same problem, but just for open)
• runtime: signal handling: Go assumes SA_RESTART, but does not enforce it #20400 (which suggests handling EINTR everywhere in the standard library)

System details

go version go1.9.2 darwin/amd64
GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/julian/go"
GORACE=""
GOROOT="/usr/local/Cellar/go/1.9.2/libexec"
GOTOOLDIR="/usr/local/Cellar/go/1.9.2/libexec/pkg/tool/darwin_amd64"
GCCGO="gccgo"
CC="clang"
GOGCCFLAGS="-fPIC -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/x1/vfmlq7554nx8t6hzhl8804p40000gn/T/go-build975276148=/tmp/go-build -gno-record-gcc-switches -fno-common"
CXX="clang++"
CGO_ENABLED="1"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOROOT/bin/go version: go version go1.9.2 darwin/amd64
GOROOT/bin/go tool compile -V: compile version go1.9.2
uname -v: Darwin Kernel Version 17.2.0: Fri Sep 29 18:27:05 PDT 2017; root:xnu-4570.20.62~3/RELEASE_X86_64
ProductName:	Mac OS X
ProductVersion:	10.13.1
BuildVersion:	17B48
lldb --version: lldb-900.0.57
  Swift-4.0

[bradfitz]

I can reproduce on Go tip (after Go 1.9) and on a macOS version one before yours:

brad5k:~ $ ./in 
^Z
[1]+  Stopped                 ./in
brad5k:~ $ fg
./in
read /dev/stdin: interrupted system call
brad5k:~ $ sw_vers 
ProductName:	Mac OS X
ProductVersion:	10.12.6
BuildVersion:	16G1036

[ianlancetaylor]

That is rather annoying. We don't install a SIGTSTP signal, nor should we. So we just take the default action. It looks like on GNU/Linux the default action is to not interrupt a read, but on MacOS it is.

[ianlancetaylor]

The fix took 10 seconds, the test case took five hours.

[gopherbot]

Change https://golang.org/cl/79215 mentions this issue: internal/poll: loop on EINTR in Read on Darwin