os/exec: add Cmd.RunContext and Cmd.WaitContext

Updates #14660

Change-Id: Ifa5c97ba327ad7ceea0a9a252e3dbd9d079dae54
Reviewed-on: https://go-review.googlesource.com/22529
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

4 files changed, 74 insertions, 3 deletions

diff --git a/src/cmd/dist/deps.go b/src/cmd/dist/deps.go
index 0838914b9c..e8dd6cf3d9 100644
--- a/src/cmd/dist/deps.go
+++ b/src/cmd/dist/deps.go
@@ -8,6 +8,7 @@ var builddeps = map[string][]string{
 	"compress/flate":                    {"bufio", "bytes", "errors", "fmt", "internal/race", "internal/syscall/windows", "internal/syscall/windows/registry", "internal/syscall/windows/sysdll", "io", "math", "os", "reflect", "runtime", "runtime/internal/atomic", "runtime/internal/sys", "sort", "strconv", "sync", "sync/atomic", "syscall", "time", "unicode", "unicode/utf16", "unicode/utf8"},
 	"compress/zlib":                     {"bufio", "bytes", "compress/flate", "errors", "fmt", "hash", "hash/adler32", "internal/race", "internal/syscall/windows", "internal/syscall/windows/registry", "internal/syscall/windows/sysdll", "io", "math", "os", "reflect", "runtime", "runtime/internal/atomic", "runtime/internal/sys", "sort", "strconv", "sync", "sync/atomic", "syscall", "time", "unicode", "unicode/utf16", "unicode/utf8"},
 	"container/heap":                    {"runtime", "runtime/internal/atomic", "runtime/internal/sys", "sort"},
+	"context":                           {"errors", "fmt", "internal/race", "internal/syscall/windows", "internal/syscall/windows/registry", "internal/syscall/windows/sysdll", "io", "math", "os", "reflect", "runtime", "runtime/internal/atomic", "runtime/internal/sys", "strconv", "sync", "sync/atomic", "syscall", "time", "unicode/utf16", "unicode/utf8"},
 	"crypto":                            {"errors", "hash", "internal/race", "io", "math", "runtime", "runtime/internal/atomic", "runtime/internal/sys", "strconv", "sync", "sync/atomic", "unicode/utf8"},
 	"crypto/sha1":                       {"crypto", "errors", "hash", "internal/race", "io", "math", "runtime", "runtime/internal/atomic", "runtime/internal/sys", "strconv", "sync", "sync/atomic", "unicode/utf8"},
 	"debug/dwarf":                       {"encoding/binary", "errors", "fmt", "internal/race", "internal/syscall/windows", "internal/syscall/windows/registry", "internal/syscall/windows/sysdll", "io", "math", "os", "path", "reflect", "runtime", "runtime/internal/atomic", "runtime/internal/sys", "sort", "strconv", "strings", "sync", "sync/atomic", "syscall", "time", "unicode", "unicode/utf16", "unicode/utf8"},
@@ -39,7 +40,7 @@ var builddeps = map[string][]string{
 	"math":                    {"runtime", "runtime/internal/atomic", "runtime/internal/sys"},
 	"net/url":                 {"bytes", "errors", "fmt", "internal/race", "internal/syscall/windows", "internal/syscall/windows/registry", "internal/syscall/windows/sysdll", "io", "math", "os", "reflect", "runtime", "runtime/internal/atomic", "runtime/internal/sys", "sort", "strconv", "strings", "sync", "sync/atomic", "syscall", "time", "unicode", "unicode/utf16", "unicode/utf8"},
 	"os":                      {"errors", "internal/race", "internal/syscall/windows", "internal/syscall/windows/registry", "internal/syscall/windows/sysdll", "io", "runtime", "runtime/internal/atomic", "runtime/internal/sys", "sync", "sync/atomic", "syscall", "time", "unicode/utf16", "unicode/utf8"},
-	"os/exec":                 {"bytes", "errors", "internal/race", "internal/syscall/windows", "internal/syscall/windows/registry", "internal/syscall/windows/sysdll", "io", "math", "os", "path/filepath", "runtime", "runtime/internal/atomic", "runtime/internal/sys", "sort", "strconv", "strings", "sync", "sync/atomic", "syscall", "time", "unicode", "unicode/utf16", "unicode/utf8"},
+	"os/exec":                 {"bytes", "context", "errors", "fmt", "internal/race", "internal/syscall/windows", "internal/syscall/windows/registry", "internal/syscall/windows/sysdll", "io", "math", "os", "path/filepath", "reflect", "runtime", "runtime/internal/atomic", "runtime/internal/sys", "sort", "strconv", "strings", "sync", "sync/atomic", "syscall", "time", "unicode", "unicode/utf16", "unicode/utf8"},
 	"os/signal":               {"errors", "internal/race", "internal/syscall/windows", "internal/syscall/windows/registry", "internal/syscall/windows/sysdll", "io", "os", "runtime", "runtime/internal/atomic", "runtime/internal/sys", "sync", "sync/atomic", "syscall", "time", "unicode/utf16", "unicode/utf8"},
 	"path":                    {"errors", "internal/race", "io", "runtime", "runtime/internal/atomic", "runtime/internal/sys", "strings", "sync", "sync/atomic", "unicode", "unicode/utf8"},
 	"path/filepath":           {"errors", "internal/race", "internal/syscall/windows", "internal/syscall/windows/registry", "internal/syscall/windows/sysdll", "io", "os", "runtime", "runtime/internal/atomic", "runtime/internal/sys", "sort", "strings", "sync", "sync/atomic", "syscall", "time", "unicode", "unicode/utf16", "unicode/utf8"},
@@ -61,5 +62,5 @@ var builddeps = map[string][]string{
 	"unicode":                 {"runtime", "runtime/internal/atomic", "runtime/internal/sys"},
 	"unicode/utf16":           {"runtime", "runtime/internal/atomic", "runtime/internal/sys"},
 	"unicode/utf8":            {"runtime", "runtime/internal/atomic", "runtime/internal/sys"},
-	"cmd/go":                  {"bufio", "bytes", "compress/flate", "compress/zlib", "container/heap", "crypto", "crypto/sha1", "debug/dwarf", "debug/elf", "debug/macho", "encoding", "encoding/base64", "encoding/binary", "encoding/json", "errors", "flag", "fmt", "go/ast", "go/build", "go/doc", "go/parser", "go/scanner", "go/token", "hash", "hash/adler32", "internal/race", "internal/singleflight", "internal/syscall/windows", "internal/syscall/windows/registry", "internal/syscall/windows/sysdll", "io", "io/ioutil", "log", "math", "net/url", "os", "os/exec", "os/signal", "path", "path/filepath", "reflect", "regexp", "regexp/syntax", "runtime", "runtime/internal/atomic", "runtime/internal/sys", "sort", "strconv", "strings", "sync", "sync/atomic", "syscall", "text/template", "text/template/parse", "time", "unicode", "unicode/utf16", "unicode/utf8"},
+	"cmd/go":                  {"bufio", "bytes", "compress/flate", "compress/zlib", "container/heap", "context", "crypto", "crypto/sha1", "debug/dwarf", "debug/elf", "debug/macho", "encoding", "encoding/base64", "encoding/binary", "encoding/json", "errors", "flag", "fmt", "go/ast", "go/build", "go/doc", "go/parser", "go/scanner", "go/token", "hash", "hash/adler32", "internal/race", "internal/singleflight", "internal/syscall/windows", "internal/syscall/windows/registry", "internal/syscall/windows/sysdll", "io", "io/ioutil", "log", "math", "net/url", "os", "os/exec", "os/signal", "path", "path/filepath", "reflect", "regexp", "regexp/syntax", "runtime", "runtime/internal/atomic", "runtime/internal/sys", "sort", "strconv", "strings", "sync", "sync/atomic", "syscall", "text/template", "text/template/parse", "time", "unicode", "unicode/utf16", "unicode/utf8"},
 }
diff --git a/src/go/build/deps_test.go b/src/go/build/deps_test.go
index 2db5ba67d1..a87de577b5 100644
--- a/src/go/build/deps_test.go
+++ b/src/go/build/deps_test.go
@@ -140,7 +140,7 @@ var pkgDeps = map[string][]string{
 	"os":            {"L1", "os", "syscall", "time", "internal/syscall/windows"},
 	"path/filepath": {"L2", "os", "syscall"},
 	"io/ioutil":     {"L2", "os", "path/filepath", "time"},
-	"os/exec":       {"L2", "os", "path/filepath", "syscall"},
+	"os/exec":       {"L2", "os", "context", "path/filepath", "syscall"},
 	"os/signal":     {"L2", "os", "syscall"},
 
 	// OS enables basic operating system functionality,
diff --git a/src/os/exec/exec.go b/src/os/exec/exec.go
index 340ebd498b..76fcba90bf 100644
--- a/src/os/exec/exec.go
+++ b/src/os/exec/exec.go
@@ -13,6 +13,7 @@ package exec
 
 import (
 	"bytes"
+	"context"
 	"errors"
 	"io"
 	"os"
@@ -262,6 +263,15 @@ func (c *Cmd) Run() error {
 	return c.Wait()
 }
 
+// RunContext is like Run, but kills the process (by calling os.Process.Kill)
+// if ctx is done before the process ends on its own.
+func (c *Cmd) RunContext(ctx context.Context) error {
+	if err := c.Start(); err != nil {
+		return err
+	}
+	return c.WaitContext(ctx)
+}
+
 // lookExtensions finds windows executable by its dir and path.
 // It uses LookPath to try appropriate extensions.
 // lookExtensions does not search PATH, instead it converts `prog` into `.\prog`.
@@ -386,6 +396,12 @@ func (e *ExitError) Error() string {
 //
 // Wait releases any resources associated with the Cmd.
 func (c *Cmd) Wait() error {
+	return c.WaitContext(nil)
+}
+
+// WaitContext is like Wait, but kills the process (by calling os.Process.Kill)
+// if ctx is done before the process ends on its own.
+func (c *Cmd) WaitContext(ctx context.Context) error {
 	if c.Process == nil {
 		return errors.New("exec: not started")
 	}
@@ -393,7 +409,22 @@ func (c *Cmd) Wait() error {
 		return errors.New("exec: Wait was already called")
 	}
 	c.finished = true
+
+	var waitDone chan struct{}
+	if ctx != nil {
+		waitDone := make(chan struct{})
+		go func() {
+			select {
+			case <-ctx.Done():
+				c.Process.Kill()
+			case <-waitDone:
+			}
+		}()
+	}
 	state, err := c.Process.Wait()
+	if waitDone != nil {
+		close(waitDone)
+	}
 	c.ProcessState = state
 
 	var copyError error
diff --git a/src/os/exec/exec_test.go b/src/os/exec/exec_test.go
index ed2721bb5e..1151ca7d0f 100644
--- a/src/os/exec/exec_test.go
+++ b/src/os/exec/exec_test.go
@@ -10,6 +10,7 @@ package exec_test
 import (
 	"bufio"
 	"bytes"
+	"context"
 	"fmt"
 	"internal/testenv"
 	"io"
@@ -835,3 +836,41 @@ func TestOutputStderrCapture(t *testing.T) {
 		t.Errorf("ExitError.Stderr = %q; want %q", got, want)
 	}
 }
+
+func TestContext(t *testing.T) {
+	c := helperCommand(t, "pipetest")
+	stdin, err := c.StdinPipe()
+	if err != nil {
+		t.Fatal(err)
+	}
+	stdout, err := c.StdoutPipe()
+	if err != nil {
+		t.Fatal(err)
+	}
+	ctx, cancel := context.WithCancel(context.Background())
+	if err := c.Start(); err != nil {
+		t.Fatal(err)
+	}
+
+	if _, err := stdin.Write([]byte("O:hi\n")); err != nil {
+		t.Fatal(err)
+	}
+	buf := make([]byte, 5)
+	n, err := io.ReadFull(stdout, buf)
+	if n != len(buf) || err != nil || string(buf) != "O:hi\n" {
+		t.Fatalf("ReadFull = %d, %v, %q", n, err, buf[:n])
+	}
+	waitErr := make(chan error, 1)
+	go func() {
+		waitErr <- c.WaitContext(ctx)
+	}()
+	cancel()
+	select {
+	case err := <-waitErr:
+		if err == nil {
+			t.Fatal("expected Wait failure")
+		}
+	case <-time.After(3 * time.Second):
+		t.Fatal("timeout waiting for child process death")
+	}
+}