os: use AddCleanup, not SetFinalizer, for Process

There is no reason to use a cleanup/finalizer for a Process that
doesn't use a handle, because Release doesn't change anything visible
about the process.

For #70907

Change-Id: I3b92809175523ceee2e07d601cc2a8e8b86321e0
Reviewed-on: https://go-review.googlesource.com/c/go/+/638579
Reviewed-by: Carlos Amedee <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Auto-Submit: Ian Lance Taylor <[email protected]>
Reviewed-by: Michael Knyszek <[email protected]>

Author: ianlancetaylor

src/os/exec.go

@@ -52,6 +52,9 @@ type Process struct {
 	// This is a pointer to a separate memory allocation
 	// so that we can use runtime.AddCleanup.
 	handle *processHandle
+
+	// cleanup is used to clean up the process handle.
+	cleanup runtime.Cleanup
 }
 
 // processHandle holds an operating system handle to a process.
@@ -111,7 +114,6 @@ func newPIDProcess(pid int) *Process {
 	p := &Process{
 		Pid: pid,
 	}
-	runtime.SetFinalizer(p, (*Process).Release)
 	return p
 }
 
@@ -128,7 +130,9 @@ func newHandleProcess(pid int, handle uintptr) *Process {
 		Pid:    pid,
 		handle: ph,
 	}
-	runtime.SetFinalizer(p, (*Process).Release)
+
+	p.cleanup = runtime.AddCleanup(p, (*processHandle).release, ph)
+
 	return p
 }
 
@@ -137,7 +141,6 @@ func newDoneProcess(pid int) *Process {
 		Pid: pid,
 	}
 	p.state.Store(uint32(statusDone)) // No persistent reference, as there is no handle.
-	runtime.SetFinalizer(p, (*Process).Release)
 	return p
 }
 
@@ -197,7 +200,12 @@ func (p *Process) handlePersistentRelease(reason processStatus) processStatus {
 		if !p.state.CompareAndSwap(state, uint32(reason)) {
 			continue
 		}
+
+		// No need for more cleanup.
+		p.cleanup.Stop()
+
 		p.handle.release()
+
 		return status
 	}
 }

src/os/exec_plan9.go

@@ -6,7 +6,6 @@ package os
 
 import (
 	"internal/itoa"
-	"runtime"
 	"syscall"
 	"time"
 )
@@ -95,8 +94,6 @@ func (p *Process) release() error {
 	// Just mark the PID unusable.
 	p.pidDeactivate(statusReleased)
 
-	// no need for a finalizer anymore
-	runtime.SetFinalizer(p, nil)
 	return nil
 }
 

src/os/exec_unix.go

@@ -8,7 +8,6 @@ package os
 
 import (
 	"errors"
-	"runtime"
 	"syscall"
 	"time"
 )
@@ -136,8 +135,7 @@ func (p *Process) release() error {
 		// Just mark the PID unusable.
 		p.pidDeactivate(statusReleased)
 	}
-	// no need for a finalizer anymore
-	runtime.SetFinalizer(p, nil)
+
 	return nil
 }
 

src/os/exec_windows.go

@@ -83,8 +83,6 @@ func (p *Process) release() error {
 		return syscall.EINVAL
 	}
 
-	// no need for a finalizer anymore
-	runtime.SetFinalizer(p, nil)
 	return nil
 }