feat(prefork): Enhance prefork management with WatchMaster, CommandProducer, and Windows support by ReneWerner87 · Pull Request #2180 · valyala/fasthttp

ReneWerner87 · 2026-04-12T18:24:32Z

We've been working on reducing code duplication between Fiber and fasthttp's prefork package. Right now Fiber maintains its own prefork implementation (~200 lines) that reimplements most of what fasthttp/prefork already does - process spawning, child management, the recovery loop - just to hook into a few lifecycle events (logging when a child spawns, showing a startup message after all workers are up, etc.).

This PR adds a small set of optional callbacks to the Prefork struct that make it possible for consumers like Fiber to plug into the prefork lifecycle without copying the whole thing:

OnChildSpawn(pid int) error - called when a new child is forked, so the caller can track PIDs or run hooks
OnMasterReady(childPIDs []int) error - called once after all children are up, useful for startup messages or metrics
OnChildRecover(pid int) error - called when a crashed child gets replaced, for logging/alerting
CommandProducer(files []*os.File) (*exec.Cmd, error) - allows overriding how child commands are created, which is useful for testing (injecting dummy commands instead of re-executing the binary)

All fields are optional and nil-safe - existing code doesn't need to change. The zero value works exactly as before.

Additionally:

listenAsChild() extracted to remove duplicated setup code across the three ListenAndServe* methods
watchMaster now handles Windows correctly (using FindProcess+Wait instead of Getppid polling, which doesn't detect parent exit on Windows)
Goroutine closures in the spawn/recovery loop pass cmd and pid as parameters instead of capturing the loop variable

You can see the practical usage in the Fiber PR that builds on this: gofiber/fiber#4210 - it replaces Fiber's entire prefork implementation with ~50 lines that configure these callbacks. The rest is handled by this package.

… management

…mands

…erveTLS

… callback comment

Integrate upstream's OnMasterDeath callback (replaces WatchMaster bool), os.Executable() for child command, and watchMaster as method on Prefork. Keep our OnChildSpawn, OnMasterReady, OnChildRecover callbacks and CommandProducer. Update tests accordingly. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

On Windows, os.Getppid() returns a static PID that doesn't change when the parent exits (no reparenting). Use FindProcess+Wait instead, which correctly detects parent exit. Also document why masterPID comparison works for Docker containers (master PID 1 case). Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

The three ListenAndServe* methods had identical child setup code (listen, set ln, watch master). Extract to listenAsChild() for cleaner code. Also add comment for the magic file descriptor number 3. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Keep upstream's (addr, certKey, certFile) signature to avoid breaking callers. Fix the doc comment to match the actual parameter order instead. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

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Pull request overview

Enhances prefork to reduce duplication in downstream consumers (e.g., Fiber) by exposing lifecycle hooks and customizable child command creation, while also improving child/master monitoring behavior on Windows.

Changes:

Added optional lifecycle callbacks (OnChildSpawn, OnMasterReady, OnChildRecover) and a CommandProducer hook for custom child command creation.
Refactored child listener setup into listenAsChild() to deduplicate logic across ListenAndServe* methods.
Updated master-watch logic to correctly detect master exit on Windows and fixed goroutine loop-variable capture in spawn/recovery.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 5 comments.

File	Description
`prefork/prefork.go`	Adds callbacks + `CommandProducer`, refactors child setup, improves Windows master monitoring, and adjusts spawn/recovery loop behavior.
`prefork/prefork_test.go`	Adds tests around logger/callback fields and `CommandProducer` usage.

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Lint fixes: - Remove unused Reuseport field write in test (govet/unusedwrite) - Replace fmt.Errorf with errors.New for static errors (perfsprint) Review feedback (Copilot): - Validate CommandProducer returns a started command (nil/Process check) - Clarify ListenAndServeTLS doc: parameter order and internal forwarding - Use hermetic test binary re-exec instead of external 'go' binary - Rename misleading test to reflect what it actually asserts Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ReneWerner87 · 2026-04-17T13:09:18Z

@erikdubbelboer WDYT?

ReneWerner87 · 2026-04-19T12:07:08Z

will check the hints and answer tomorrow, thx

ReneWerner87 · 2026-04-20T07:28:16Z

I will implement the changes suggested in the comments

- watchMaster: log errors from FindProcess/Wait instead of swallowing - watchMaster: don't call OnMasterDeath if FindProcess fails - OnChildRecover: change signature to func(pid int), drop unused error return - OnChildSpawn: add comment clarifying deferred cleanup handles the child - CommandProducer: improve docs describing contract and use cases Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ReneWerner87 · 2026-04-20T08:55:00Z

ready for a recheck @erikdubbelboer

- OnChildRecover: signature changed to func(oldPid, newPid int) so callers can track which process was replaced - OnChildSpawn: also called for recovered children (a recovered child is still a spawned child) - watchMaster: call OnMasterDeath when FindProcess fails (process is most likely gone) - CommandProducer: document that FASTHTTP_PREFORK_CHILD=1 must be set in the child env, and what the default does when nil Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ReneWerner87 · 2026-04-27T08:50:42Z

@erikdubbelboer something else or ready for merge ?

- Move Wait() goroutine before OnChildSpawn so Kill()+Wait() works correctly if a callback fails and the deferred cleanup runs - Add Wait() call in deferred cleanup after Kill() to reap children - Same fix in recovery loop - Remove shallow callback tests that only tested Go compiler - Add Test_Prefork_Lifecycle: runs full prefork with CommandProducer, verifies callbacks fire in correct order with correct arguments Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ReneWerner87 · 2026-04-29T07:05:47Z

All feedback addressed:

Wait goroutine now starts before OnChildSpawn (both in spawn and recovery loop) to avoid zombies
Added Wait() in deferred cleanup after Kill()
Removed the shallow callback tests, replaced with Test_Prefork_Lifecycle that runs the full prefork loop and verifies callback order/arguments

Ready for another look @erikdubbelboer

Addresses outstanding review concerns and several adjacent issues surfaced during a follow-up review pass. Lifecycle / supervision - Track every per-child Wait goroutine via sync.WaitGroup and unblock pending sigCh sends through a context.Cancel so early-return paths (OnChildSpawn / OnMasterReady error, recovery doCommand error, ErrOverRecovery) can no longer leak goroutines or stall children. - Install signal.Notify(SIGTERM, SIGINT) in the master so deploy/ rolling-restart signals enter the shutdown path instead of killing the master without graceful teardown. - Replace the unconditional SIGKILL defer with a SIGTERM-then-SIGKILL sequence gated by a configurable ShutdownGracePeriod (defaults to 5s, Windows path stays SIGKILL since Signal(SIGTERM) is unsupported). API - OnChildRecover now returns error so callers can implement recovery policies (circuit-breaker etc.); panic in any hook is recovered and surfaced as the returned error, with diagnostic logging. - Add RecoverInterval (optional crash-loop backoff) and ShutdownGracePeriod fields with safe zero-value defaults. - Export ErrCommandProducerNilCmd and ErrCommandProducerNotStarted sentinel errors so callers can errors.Is them. - Rename oldPid/newPid to oldPID/newPID per Go initialism convention. - Logger interface now declares an explicit compile-time compatibility check with fasthttp.Logger. Resource hygiene - Master closes both the original tcpListener and the duped fd in p.files when prefork() returns; previously the duped fd leaked once per call. - doCommand wraps every error path with %w + fmt.Errorf so caller-side diagnostics keep stage context. - Strip pre-existing FASTHTTP_PREFORK_CHILD entries before appending so child env never carries duplicate keys. - Extract magic numbers as package constants (inheritedListenerFD, masterPollInterval, defaultShutdownGracePeriod, preforkChildEnvValue). - Rename the inherited listener fd via os.NewFile so net.FileListener errors are diagnosable. Tests - Migrate to t.Setenv (drop the global setUp/tearDown helpers) — fixes the env-mutation-vs-parallel race. - Replace rand.Intn port helper with `:0` + Listener.Addr() to remove port-collision flakes under -count and parallel runs. - Collapse the three near-identical Test_ListenAndServe* tests into a single table-driven subtest that actually asserts the args forwarded to ServeFunc/ServeTLSFunc/ServeTLSEmbedFunc. - Add coverage for the previously untested branches: CommandProducer returning err / nil cmd / unstarted cmd, initial OnChildSpawn error, OnMasterReady error, hook panic surfacing, RecoverInterval enforcement. - noopChildProducer helper kills + waits any spawned child binaries during cleanup so failed tests no longer leave subprocesses around.

erikdubbelboer · 2026-05-02T11:17:44Z

Thanks! I'll tag a new release next week.

erikdubbelboer · 2026-05-02T11:20:29Z

I now see that you pushed another commit right between me checking your previous commit and merging this. Github didn't show this 😠

ReneWerner87 · 2026-05-02T12:01:41Z

Oh, sorry, I didn't realize you were about to merge. Usually a little time passes before that happens.

Feel free to review the last commit again, and I'll fix whatever you notice.

erikdubbelboer · 2026-05-02T12:20:15Z

I have reverted that commit on master: e9208ec
Please make a new pull request for these changes.

ReneWerner87 · 2026-05-02T13:52:20Z

ok

ReneWerner87 and others added 8 commits January 28, 2026 08:50

feat(prefork): add WatchMaster and callback support for child process…

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… management

feat(prefork): add CommandProducer for customizable child process com…

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…mands

refactor(prefork): improve comments and parameter order in ListenAndS…

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…erveTLS

refactor(prefork): enhance logging message and clarify OnChildRecover…

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… callback comment

fix(prefork): restore upstream ListenAndServeTLS parameter order

c1055ce

Keep upstream's (addr, certKey, certFile) signature to avoid breaking callers. Fix the doc comment to match the actual parameter order instead. Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Copilot AI review requested due to automatic review settings April 12, 2026 18:24

ReneWerner87 mentioned this pull request Apr 12, 2026

🔥 feat(prefork): delegate implementation to fasthttp/prefork gofiber/fiber#4210

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ReneWerner87 and others added 2 commits April 25, 2026 12:36

Merge branch 'master' into prefork_optimization

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ReneWerner87 added 2 commits April 29, 2026 11:00

fix(prefork): ensure recovery default stays positive

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test(prefork): isolate lifecycle tests

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fix(prefork): tighten recovery callback flow

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erikdubbelboer merged commit 481e579 into valyala:master May 2, 2026
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ReneWerner87 mentioned this pull request May 2, 2026

feat(prefork): graceful shutdown, leak fixes, hook robustness (re-open of #2180 follow-up) #2199

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