Fix delay with flicking through files or commits when git diff is very slow

pkg/commands/oscommands/os.go

@@ -1,7 +1,6 @@
 package oscommands
 
 import (
-	"fmt"
 	"io"
 	"os"
 	"os/exec"
@@ -329,15 +328,3 @@ func GetLazygitPath() string {
 	}
 	return `"` + filepath.ToSlash(ex) + `"`
 }
-
-func (c *OSCommand) UpdateWindowTitle() error {
-	if c.Platform.OS != "windows" {
-		return nil
-	}
-	path, getWdErr := os.Getwd()
-	if getWdErr != nil {
-		return getWdErr
-	}
-	argString := fmt.Sprint("title ", filepath.Base(path), " - Lazygit")
-	return c.Cmd.NewShell(argString, c.UserConfig().OS.ShellFunctionsFile).Run()
-}

pkg/commands/oscommands/os_default_platform.go

@@ -5,8 +5,10 @@ package oscommands
 
 import (
 	"os"
+	"os/exec"
 	"runtime"
 	"strings"
+	"syscall"
 )
 
 func GetPlatform() *Platform {
@@ -34,3 +36,15 @@ func getUserShell() string {
 
 	return "bash"
 }
+
+func (c *OSCommand) UpdateWindowTitle() error {
+	return nil
+}
+
+func TerminateProcessGracefully(cmd *exec.Cmd) error {
+	if cmd.Process == nil {
+		return nil
+	}
+
+	return cmd.Process.Signal(syscall.SIGTERM)
+}

pkg/commands/oscommands/os_windows.go

@@ -1,9 +1,30 @@
 package oscommands
 
+import (
+	"fmt"
+	"os"
+	"os/exec"
+	"path/filepath"
+)
+
 func GetPlatform() *Platform {
 	return &Platform{
 		OS:       "windows",
 		Shell:    "cmd",
 		ShellArg: "/c",
 	}
 }
+
+func (c *OSCommand) UpdateWindowTitle() error {
+	path, getWdErr := os.Getwd()
+	if getWdErr != nil {
+		return getWdErr
+	}
+	argString := fmt.Sprint("title ", filepath.Base(path), " - Lazygit")
+	return c.Cmd.NewShell(argString, c.UserConfig().OS.ShellFunctionsFile).Run()
+}
+
+func TerminateProcessGracefully(cmd *exec.Cmd) error {
+	// Signals other than SIGKILL are not supported on Windows
+	return nil
+}

pkg/tasks/tasks.go

@@ -9,6 +9,7 @@ import (
 	"time"
 
 	"github.com/jesseduffield/gocui"
+	"github.com/jesseduffield/lazygit/pkg/commands/oscommands"
 	"github.com/jesseduffield/lazygit/pkg/utils"
 	"github.com/sasha-s/go-deadlock"
 	"github.com/sirupsen/logrus"
@@ -165,6 +166,17 @@ func (self *ViewBufferManager) NewCmdTask(start func() (*exec.Cmd, io.Reader), p
 				// and the user is flicking through a bunch of items.
 				self.throttle = time.Since(startTime) < THROTTLE_TIME && timeToStart > COMMAND_START_THRESHOLD
 
+				// Kill the still-running command. The only reason to do this is to save CPU usage
+				// when flicking through several very long diffs when diff.algorithm = histogram is
+				// being used, in which case multiple git processes continue to calculate expensive
+				// diffs in the background even though they have been stopped already.
+				//
+				// Unfortunately this will do nothing on Windows, so Windows users will have to live
+				// with the higher CPU usage.
+				if err := oscommands.TerminateProcessGracefully(cmd); err != nil {
+					self.Log.Errorf("error when trying to terminate cmd task: %v; Command: %v %v", err, cmd.Path, cmd.Args)
+				}
+
 				// close the task's stdout pipe (or the pty if we're using one) to make the command terminate
 				onDone()
 			}
@@ -291,11 +303,15 @@ func (self *ViewBufferManager) NewCmdTask(start func() (*exec.Cmd, io.Reader), p
 
 			refreshViewIfStale()
 
-			if err := cmd.Wait(); err != nil {
-				select {
-				case <-opts.Stop:
-					// it's fine if we've killed this program ourselves
-				default:
+			select {
+			case <-opts.Stop:
+				// If we stopped the task, don't block waiting for it; this could cause a delay if
+				// the process takes a while until it actually terminates. We still want to call
+				// Wait to reclaim any resources, but do it on a background goroutine, and ignore
+				// any errors.
+				go func() { _ = cmd.Wait() }()
+			default:
+				if err := cmd.Wait(); err != nil {
 					self.Log.Errorf("Unexpected error when running cmd task: %v; Failed command: %v %v", err, cmd.Path, cmd.Args)
 				}
 			}