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WalkthroughPlugin startup and shutdown now terminate plugin process groups, bound process reaping, remove sockets during cleanup, and report incomplete cleanup. Unix integration tests cover descendant cleanup, escaped descendants, startup failures, and healthy plugin startup. ChangesPlugin process cleanup
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Suggested reviewers: Priority: ➖ Normal Change: Bug fix · Severity of issue fixed: Medium Merge Risk: 🟡 Moderate · up to The plugin shutdown path can, in a narrow PID-reuse race, terminate an unrelated process group. Use stable process containment before merging. 🚥 Pre-merge checks | ✅ 5✅ Passed checks (5 passed)
✨ Finishing Touches🧪 Generate unit tests (beta)
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peteski22
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peteski22
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This branch was cut before #299 merged, so most of this diff is already on main: the process_*.go files, the startPlugin cleanup test, and most of the fixture. After a rebase, what remains is the stop() change, the new stop test, and the new fixture mode. Most comments are there. The two on startPlugin are about how it sets up the command that stop() depends on.
Two things should be fixed before merge. When the post-kill wait times out, stop() returns nil after giving up. And the new test passes with or without that bound. The rest are smaller and fit in this PR, apart from the process group ID note on killProcessGroup, which is a follow-up.
| @@ -256,13 +256,29 @@ func (p *runningPlugin) stop() error { | |||
| var processExitErr error | |||
| select { | |||
| case <-time.After(pluginForceKillTimeout): | |||
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Should fix in this PR: pluginForceKillTimeout now bounds three different waits: the grace period before the kill here, the reap wait at L276, and the reap wait in startPlugin's cleanup defer at L431. Its doc comment only describes the first. Raising it to give slow plugins more time would also lengthen both post-kill waits. Splitting it into two constants, such as pluginExitGraceTimeout and pluginReapTimeout, each documented for the wait it bounds, keeps those separate.
| if err := killProcessGroup(p.cmd); err != nil && !errors.Is(err, os.ErrProcessDone) { | ||
| // Only report if we couldn't kill a stuck process. | ||
| return fmt.Errorf("failed to force kill stuck plugin process: %w", err) |
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Should fix in this PR: this early return skips the unix socket removal below and abandons the Wait goroutine. A failed kill is the case where the plugin is most likely still running and still bound to that socket. Keep the error, but record it, let the rest of the cleanup run, and errors.Join it into the return. Moving the socket removal into a defer near the top of stop() works too.
| // cmd.Wait() also waits for the stdout/stderr copy goroutines (Stdout | ||
| // and Stderr are non-file hclog writers), so a descendant that | ||
| // inherited either fd can hold Wait open after the plugin process | ||
| // itself is dead. Bound this second wait too, or StopPlugins blocks | ||
| // daemon shutdown forever on exactly the case the force kill exists | ||
| // to handle. |
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Nit: the project comment rules ask comments not to reference callers or downstream behavior. The first sentence already explains why this wait needs a bound.
| // cmd.Wait() also waits for the stdout/stderr copy goroutines (Stdout | |
| // and Stderr are non-file hclog writers), so a descendant that | |
| // inherited either fd can hold Wait open after the plugin process | |
| // itself is dead. Bound this second wait too, or StopPlugins blocks | |
| // daemon shutdown forever on exactly the case the force kill exists | |
| // to handle. | |
| // cmd.Wait() also waits for the stdout/stderr copy goroutines (Stdout | |
| // and Stderr are non-file hclog writers), so a descendant that | |
| // inherited either fd can hold Wait open after the plugin process | |
| // itself is dead. Bound this second wait too. |
| // to handle. | ||
| select { | ||
| case processExitErr = <-done: | ||
| case <-time.After(pluginForceKillTimeout): |
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Blocking: when this times out, processExitErr is still nil, so stop() logs "plugin stopped successfully" and returns nil right after warning that the process wasn't reaped. The case this branch exists for gets reported as a clean stop, and the Wait goroutine, both stdout/stderr copy goroutines, and the pipe fds are left behind.
This should return an error. A sentinel keeps it checkable:
var errPluginCleanupIncomplete = errors.New("plugin process cleanup did not complete after force kill")Set a flag in this arm and return the sentinel after the socket cleanup. Keep it out of processExitErr: that path would log it as "exited with unexpected error", which describes a different failure.
The docstring on stop() (L229) still says it "waits for process exit", so that needs updating to match.
| "timeout", pluginForceKillTimeout, | ||
| ) | ||
| } | ||
| case processExitErr = <-done: |
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Should fix in this PR: killProcessGroup only runs on the timeout arm. If the plugin process exits within pluginForceKillTimeout, Wait returns here and the group is never signaled, so any descendant that isn't holding the inherited stdout/stderr outlives the daemon. That is the common case on shutdown (see L377).
The comments at L259-262, L379-380, and on setProcessGroup in process_unix.go all say descendants get cleaned up. They should say what the code guarantees: on the force-kill path, processes still in the plugin's process group are killed.
| @@ -360,6 +376,10 @@ func (m *Manager) startPlugin(ctx context.Context, name string, binaryPath strin | |||
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| cmd := exec.CommandContext(ctx, binaryPath, "--address", address, "--network", network) | |||
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Should fix in this PR: exec.CommandContext sets a default Cancel that kills only the plugin process. This ctx is a child of the daemon's shutdown context, and StartAndManage only runs its deferred stopPlugins() after runGroup.Wait() returns. So on a signal-driven shutdown the plugin process is already dead when stop() runs. The Stop RPC has nothing to talk to, and unless a descendant holds the pipes, Wait returns on the non-timeout arm at L282 and the group kill never happens. That ordering predates this PR, but without a fix the new group kill is rarely reached in production.
Setting Cancel before Start makes context cancellation use the same policy:
cmd.Cancel = func() error { return killProcessGroup(cmd) }killProcessGroup falls back to Process.Kill, and os/exec treats an os.ErrProcessDone from Cancel as a normal exit, so the existing exit handling still applies.
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| // Run the plugin in its own process group so cleanup can terminate any | ||
| // descendants it spawns, not just the direct child. | ||
| setProcessGroup(cmd) |
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Should fix in this PR: when the bounded waits in stop() and in the cleanup defer time out, the Wait goroutine and both pipe-copy goroutines stay blocked for as long as the descendant lives. Setting cmd.WaitDelay here releases them: once the process has exited, os/exec closes the pipes after the delay and Wait returns.
It works alongside the selects rather than replacing them. The WaitDelay timer only starts once the process has exited or the context is done, so it can't bound a kill that didn't take effect. And after a SIGKILL, Wait returns the signal's ExitError, not exec.ErrWaitDelay, so it won't tell you a descendant held the pipes.
Two details:
- Make
WaitDelaylonger than the post-kill bound instop(). If they're equal,Waitcan return theExitErrorjust as the timer fires, and the select can take that arm and report a clean stop. - Don't add
exec.ErrWaitDelaytoisExpectedShutdownError. It means pipe cleanup didn't finish.
| deadline := pluginGracefulStopTimeout + 2*pluginForceKillTimeout + 3*time.Second | ||
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| start := time.Now() | ||
| stopErr := plg.stop() | ||
| elapsed := time.Since(start) | ||
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| require.NoError(t, stopErr) | ||
| require.Less(t, elapsed, deadline, | ||
| "stop must not block indefinitely on a descendant holding the plugin's stdout/stderr open") |
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Blocking: this test can't fail for the regression it describes.
- The fixture's descendant stays in the plugin's process group, so
killProcessGroupkills both andWaitreturns long before the post-kill bound. With the innerselectinstop()replaced by a plainprocessExitErr = <-done, this test still passes, in about the same 3.2s. stop()runs on the test goroutine. If it never returned,elapsedwould never be computed, so the failure would be the package-timeoutpanic rather than this assertion.require.NoErrortreats giving up on the reap as success.BasePlugin.Stopreturns immediately, so thepluginGracefulStopTimeoutterm indeadlineis never spent.
It's still a useful test for the group kill, so it's worth keeping. For the bounded wait, add a fixture mode whose descendant calls Setsid, so it leaves the group but keeps stdout/stderr open. SysProcAttr.Setsid is Unix-only, so that needs a build-tagged file in the fixture. Then bound the call in the test:
done := make(chan error, 1)
go func() { done <- plg.stop() }()
select {
case err := <-done:
require.ErrorIs(t, err, errPluginCleanupIncomplete)
case <-time.After(2*pluginForceKillTimeout + 2*time.Second):
t.Fatal("stop did not return: the post-kill wait is unbounded")
}The pkill -f cleanup that newFixturePlugin registers matches on the binary path, so it will still kill a descendant that has left the group.
| // killProcessGroup sends SIGKILL to the process group led by cmd's process, | ||
| // falling back to killing just the process if the group signal fails (e.g. | ||
| // setProcessGroup was never applied, or the group is already gone). | ||
| func killProcessGroup(cmd *exec.Cmd) error { | ||
| if cmd.Process == nil { | ||
| return nil | ||
| } | ||
| if err := syscall.Kill(-cmd.Process.Pid, syscall.SIGKILL); err == nil { |
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Follow-up: this signals a process group ID, not a handle to the plugin's group.
- Once the leader has been reaped and the group is empty, that ID can be reused.
stop()can get here after the reap: for example, the plugin exits on its own but a descendant outside the group still holds the pipes, soWaithasn't returned when the timer fires. Checkingdonefirst would narrow that window but not close it. - A descendant that calls
setsidorsetpgidleaves the group and isn't touched.
A line in this doc comment covering both is enough for this PR. Real containment needs an OS-level handle, like pidfds or cgroups on Linux and Job Objects on Windows, and belongs in its own issue.
| // Command fixtureplugin is a test-only plugin binary used by | ||
| // internal/plugin's manager tests to exercise startPlugin's post-spawn | ||
| // failure paths against a real process and a real gRPC socket. |
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Nit: this still says the binary exists to exercise startPlugin's post-spawn failure paths. modeHealthyWithDescendant is there for stop(), so the summary should cover both.
Fixes mozilla-ai#310. stop() force-killed with p.cmd.Process.Kill(), which signals only the direct child, then waited on `processExitErr = <-done` with no timeout. Two consequences, both on the graceful shutdown path that StopPlugins takes. Descendants leak. Plugins are started with setProcessGroup, and startPlugin's cleanup defer already uses killProcessGroup, but only when startup fails. A plugin that starts successfully and later spawns descendants left all of them running when the daemon shut down normally. stop() now calls killProcessGroup(p.cmd), so the whole group goes. stop() could hang forever. cmd.Wait() also waits on the stdout/stderr copy goroutines (both are non-file hclog writers), so a descendant that inherited either fd holds Wait open after the plugin process is already dead, and the unbounded `<-done` never returns. That is precisely the case the force kill exists to handle, so the wait after it now gets the same select + pluginForceKillTimeout bound startPlugin uses, and logs when it expires. Test: TestManager_stop_KillsDescendantsAndReturnsWithinDeadline, in a new manager_stop_cleanup_unix_test.go alongside the existing startPlugin cleanup tests and sharing their helpers. It starts a plugin in the new healthy-with-descendant fixture mode, which forks the blocking descendant and then serves normally, so the plugin reaches the running state and is only torn down later by stop(). Against unpatched sources it does not merely fail, it hangs, which is the bug: panic: test timed out after 45s FAIL github.com/mozilla-ai/mcpd/internal/plugin 45.019s With the fix, PASS in 2.58s. One caveat on running it: a hung pre-fix run is killed before its cleanups, so it leaves a stale socket behind. generateAddress names sockets plugin-<basename>-<id>.sock under os.TempDir() with a per-Manager counter, so the next run picks the same name and fails with "plugin didn't start in time" instead of anything useful. Clear /tmp/plugin-fixture-*.sock between a failing run and the next. go build ./... and go vet ./internal/plugin clean. go test ./internal/plugin -count=1: ok, 2.658s, all 6 integration tests pass.
Address peteski22's review on mozilla-ai#320: - stop() now returns errPluginCleanupIncomplete when the post-kill reap times out, instead of falling through to "stopped successfully" with processExitErr still nil - rewrite the stop cleanup test so it actually exercises that path: a new healthy-with-escaped-descendant fixture mode setsids its descendant out of the plugin's process group, so killProcessGroup can't reach it and the reap always times out; the test bounds stop() on its own goroutine and asserts the sentinel, and fails (proven) without the fix - split pluginForceKillTimeout into pluginExitGraceTimeout and pluginReapTimeout, each documented for the one wait it now bounds - also signal the process group on the common (no-timeout) exit path, not just after a force kill, so descendants don't survive a graceful stop - record a failed force-kill instead of returning early, so socket cleanup and the reap wait still run; errors.Join it into the result - set cmd.Cancel before Start so context cancellation kills the process group too, and set cmd.WaitDelay so a stuck descendant can't hold the Wait/copy goroutines open forever - correct the stop()/startPlugin/setProcessGroup comments to describe what the code actually guarantees, and note the process-group-ID reuse and setsid/setpgid gaps on killProcessGroup as a follow-up
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Inline comments:
In `@internal/plugin/manager.go`:
- Around line 309-311: Update stop()’s killProcessGroup handling to assign any
error other than os.ErrProcessDone to killErr, while retaining the existing
warning log. Ensure the later return paths propagate killErr so stop() reports
failed process-group cleanup instead of returning nil.
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internal/plugin/manager.gointernal/plugin/manager_startplugin_cleanup_unix_test.gointernal/plugin/manager_stop_cleanup_unix_test.gointernal/plugin/process_unix.gointernal/plugin/testdata/fixtureplugin/main.gointernal/plugin/testdata/fixtureplugin/spawn_other.gointernal/plugin/testdata/fixtureplugin/spawn_unix.go
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Inline comments:
In `@internal/plugin/manager.go`:
- Line 311: Update the post-cmd.Wait() cleanup path around killProcessGroup to
avoid signalling the recycled process-group ID derived from p.cmd.Process.Pid.
Use a stable OS-level group handle, such as the platform-equivalent mechanism
documented by process_unix.go, for cleanup after the plugin leader is reaped;
preserve the existing killErr handling while ensuring unrelated process groups
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Description
runningPlugin.stop()force-killed withp.cmd.Process.Kill(), which signals only the direct child, then waited onprocessExitErr = <-donewith no timeout. Two consequences, both on the graceful shutdown pathStopPluginstakes.Descendants leak. Plugins are started with
setProcessGroup, andstartPlugin's cleanup defer already useskillProcessGroup, but only on the startup-failure path. A plugin that starts successfully and later spawns descendants left all of them running when the daemon shut down normally.stop()now callskillProcessGroup(p.cmd).stop()could hang forever.cmd.Wait()also waits on the stdout/stderr copy goroutines (both are non-file hclog writers), so a descendant that inherited either fd holdsWaitopen after the plugin process is already dead, and the unbounded<-donenever returns. That is precisely the case the force kill exists to handle, so the wait after it now takes the sameselect+pluginForceKillTimeoutboundstartPluginuses, and logs when it expires.This stacks on #299.
killProcessGroupandsetProcessGroupare added there and do not exist onmainyet, so this branch is cut from #299 and should merge after it. The first commit here is #299's; only88e22b8is new.The test, and why it is a real one
TestManager_stop_KillsDescendantsAndReturnsWithinDeadlinelives in a newmanager_stop_cleanup_unix_test.gonext to the existingstartPlugincleanup tests and shares their helpers. It starts a plugin in a newhealthy-with-descendantfixture mode, which forks the blocking descendant and then serves normally, so the plugin reaches the running state and is only torn down later bystop().Against unpatched sources it does not merely fail, it hangs, which is the bug:
With the fix,
PASSin 2.58s.One caveat if you run it: a hung pre-fix run is killed before its cleanups, so it leaves a stale socket behind.
generateAddressnames socketsplugin-<basename>-<id>.sockunderos.TempDir()with a per-Manager counter, so the next run picks the same name and fails withplugin didn't start in timerather than anything informative. Clear/tmp/plugin-fixture-*.sockbetween a failing run and the next. Moving that address undert.TempDir()would remove the sharp edge, but it is out of scope here.PR Type
Relevant issues
Fixes #310
Checklist
make lint,make test).On checks:
go build ./...,go vet ./internal/plugin,gofmt -landgofumpt -lon the three changed files are all clean, andgo test ./internal/plugin -count=1passes (2.658s, all 6 integration tests).make lint's NOTICE step passes, but itsgolangci-lint runstep cannot complete on this machine: golangci-lint 2.10.1 is built with go1.26 and my toolchain is go1.27.1, so it panics withfile requires newer Go version go1.27 (application built with go1.26)before linting anything. That is a local toolchain mismatch rather than anything about this change, and CI's own lint job is the real signal.AI Usage
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Any additional AI details you'd like to share:
Same as #299.
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Summary by CodeRabbit
Bug Fixes
Tests