fix(process): reap entire process group on cmd.Cancel (#39143)

Signed-off-by: Royce Remer <royceremer@gmail.com>
Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

modules/process/command_unix.go

@@ -0,0 +1,32 @@
+// Copyright 2026 The Gitea Authors. All rights reserved.
+// SPDX-License-Identifier: MIT
+
+//go:build unix
+
+package process
+
+import (
+	"os/exec"
+	"syscall"
+
+	"gitea.dev/modules/util"
+)
+
+func setSysProcAttribute(cmd *exec.Cmd) {
+	// When Gitea runs SubProcessA -> SubProcessB and SubProcessA gets killed by context cancel,
+	// use process group to make sure the sub processes can be killed and reaped instead of leaving defunct(zombie) processes.
+	cmd.SysProcAttr = &syscall.SysProcAttr{Setpgid: true}
+}
+
+func (c *Cmd) onCancel() error {
+	if c.onCancelUserFunc != nil {
+		if err := c.onCancelUserFunc(); err != nil {
+			return err
+		}
+	}
+	sig := util.Iif(c.termGraceful, syscall.SIGTERM, syscall.SIGKILL)
+	// kill the whole process group
+	// ATTENTION: do not access PID after Wait or in other goroutine, it will just cause PID reuse data-race.
+	// There is no easy solution to implement "first SIGTERM then SIGKILL" in a safe way, only one signal can be sent to the process group.
+	return syscall.Kill(-c.Process.Pid, sig)
+}