feat(shared): add Effect-idiomatic file lock (EffectFlock) (#22681)

kitlangton · web-flow · commit a147ad68e6ae · 2026-04-16T00:55:14.000Z
diff --git a/packages/shared/src/util/effect-flock.ts b/packages/shared/src/util/effect-flock.ts
@@ -0,0 +1,278 @@
+import path from "path"
+import os from "os"
+import { randomUUID } from "crypto"
+import { Context, Effect, Function, Layer, Option, Schedule, Schema } from "effect"
+import type { FileSystem, Scope } from "effect"
+import type { PlatformError } from "effect/PlatformError"
+import { AppFileSystem } from "../filesystem"
+import { Global } from "../global"
+import { Hash } from "./hash"
+
+export namespace EffectFlock {
+  // ---------------------------------------------------------------------------
+  // Errors
+  // ---------------------------------------------------------------------------
+
+  export class LockTimeoutError extends Schema.TaggedErrorClass<LockTimeoutError>()("LockTimeoutError", {
+    key: Schema.String,
+  }) {}
+
+  export class LockCompromisedError extends Schema.TaggedErrorClass<LockCompromisedError>()("LockCompromisedError", {
+    detail: Schema.String,
+  }) {}
+
+  class ReleaseError extends Schema.TaggedErrorClass<ReleaseError>()("ReleaseError", {
+    detail: Schema.String,
+    cause: Schema.optional(Schema.Defect),
+  }) {
+    override get message() {
+      return this.detail
+    }
+  }
+
+  /** Internal: signals "lock is held, retry later". Never leaks to callers. */
+  class NotAcquired extends Schema.TaggedErrorClass<NotAcquired>()("NotAcquired", {}) {}
+
+  export type LockError = LockTimeoutError | LockCompromisedError
+
+  // ---------------------------------------------------------------------------
+  // Timing (baked in — no caller ever overrides these)
+  // ---------------------------------------------------------------------------
+
+  const STALE_MS = 60_000
+  const TIMEOUT_MS = 5 * 60_000
+  const BASE_DELAY_MS = 100
+  const MAX_DELAY_MS = 2_000
+  const HEARTBEAT_MS = Math.max(100, Math.floor(STALE_MS / 3))
+
+  const retrySchedule = Schedule.exponential(BASE_DELAY_MS, 1.7).pipe(
+    Schedule.either(Schedule.spaced(MAX_DELAY_MS)),
+    Schedule.jittered,
+    Schedule.while((meta) => meta.elapsed < TIMEOUT_MS),
+  )
+
+  // ---------------------------------------------------------------------------
+  // Lock metadata schema
+  // ---------------------------------------------------------------------------
+
+  const LockMetaJson = Schema.fromJsonString(
+    Schema.Struct({
+      token: Schema.String,
+      pid: Schema.Number,
+      hostname: Schema.String,
+      createdAt: Schema.String,
+    }),
+  )
+
+  const decodeMeta = Schema.decodeUnknownSync(LockMetaJson)
+  const encodeMeta = Schema.encodeSync(LockMetaJson)
+
+  // ---------------------------------------------------------------------------
+  // Service
+  // ---------------------------------------------------------------------------
+
+  export interface Interface {
+    readonly acquire: (key: string, dir?: string) => Effect.Effect<void, LockError, Scope.Scope>
+    readonly withLock: {
+      (key: string, dir?: string): <A, E, R>(body: Effect.Effect<A, E, R>) => Effect.Effect<A, E | LockError, R>
+      <A, E, R>(body: Effect.Effect<A, E, R>, key: string, dir?: string): Effect.Effect<A, E | LockError, R>
+    }
+  }
+
+  export class Service extends Context.Service<Service, Interface>()("EffectFlock") {}
+
+  // ---------------------------------------------------------------------------
+  // Layer
+  // ---------------------------------------------------------------------------
+
+  function wall() {
+    return performance.timeOrigin + performance.now()
+  }
+
+  const mtimeMs = (info: FileSystem.File.Info) => Option.getOrElse(info.mtime, () => new Date(0)).getTime()
+
+  const isPathGone = (e: PlatformError) => e.reason._tag === "NotFound" || e.reason._tag === "Unknown"
+
+  export const layer: Layer.Layer<Service, never, Global.Service | AppFileSystem.Service> = Layer.effect(
+    Service,
+    Effect.gen(function* () {
+      const global = yield* Global.Service
+      const fs = yield* AppFileSystem.Service
+      const lockRoot = path.join(global.state, "locks")
+      const hostname = os.hostname()
+      const ensuredDirs = new Set<string>()
+
+      // -- helpers (close over fs) --
+
+      const safeStat = (file: string) =>
+        fs.stat(file).pipe(
+          Effect.catchIf(isPathGone, () => Effect.void),
+          Effect.orDie,
+        )
+
+      const forceRemove = (target: string) => fs.remove(target, { recursive: true }).pipe(Effect.ignore)
+
+      /** Atomic mkdir — returns true if created, false if already exists, dies on other errors. */
+      const atomicMkdir = (dir: string) =>
+        fs.makeDirectory(dir, { mode: 0o700 }).pipe(
+          Effect.as(true),
+          Effect.catchIf(
+            (e) => e.reason._tag === "AlreadyExists",
+            () => Effect.succeed(false),
+          ),
+          Effect.orDie,
+        )
+
+      /** Write with exclusive create — compromised error if file already exists. */
+      const exclusiveWrite = (filePath: string, content: string, lockDir: string, detail: string) =>
+        fs.writeFileString(filePath, content, { flag: "wx" }).pipe(
+          Effect.catch(() =>
+            Effect.gen(function* () {
+              yield* forceRemove(lockDir)
+              return yield* new LockCompromisedError({ detail })
+            }),
+          ),
+        )
+
+      const cleanStaleBreaker = Effect.fnUntraced(function* (breakerPath: string) {
+        const bs = yield* safeStat(breakerPath)
+        if (bs && wall() - mtimeMs(bs) > STALE_MS) yield* forceRemove(breakerPath)
+        return false
+      })
+
+      const ensureDir = Effect.fnUntraced(function* (dir: string) {
+        if (ensuredDirs.has(dir)) return
+        yield* fs.makeDirectory(dir, { recursive: true }).pipe(Effect.orDie)
+        ensuredDirs.add(dir)
+      })
+
+      const isStale = Effect.fnUntraced(function* (lockDir: string, heartbeatPath: string, metaPath: string) {
+        const now = wall()
+
+        const hb = yield* safeStat(heartbeatPath)
+        if (hb) return now - mtimeMs(hb) > STALE_MS
+
+        const meta = yield* safeStat(metaPath)
+        if (meta) return now - mtimeMs(meta) > STALE_MS
+
+        const dir = yield* safeStat(lockDir)
+        if (!dir) return false
+
+        return now - mtimeMs(dir) > STALE_MS
+      })
+
+      // -- single lock attempt --
+
+      type Handle = { token: string; metaPath: string; heartbeatPath: string; lockDir: string }
+
+      const tryAcquireLockDir = Effect.fn("EffectFlock.tryAcquire")(function* (lockDir: string) {
+        const token = randomUUID()
+        const metaPath = path.join(lockDir, "meta.json")
+        const heartbeatPath = path.join(lockDir, "heartbeat")
+
+        // Atomic mkdir — the POSIX lock primitive
+        const created = yield* atomicMkdir(lockDir)
+
+        if (!created) {
+          if (!(yield* isStale(lockDir, heartbeatPath, metaPath))) return yield* new NotAcquired()
+
+          // Stale — race for breaker ownership
+          const breakerPath = lockDir + ".breaker"
+
+          const claimed = yield* fs.makeDirectory(breakerPath, { mode: 0o700 }).pipe(
+            Effect.as(true),
+            Effect.catchIf(
+              (e) => e.reason._tag === "AlreadyExists",
+              () => cleanStaleBreaker(breakerPath),
+            ),
+            Effect.catchIf(isPathGone, () => Effect.succeed(false)),
+            Effect.orDie,
+          )
+
+          if (!claimed) return yield* new NotAcquired()
+
+          // We own the breaker — double-check staleness, nuke, recreate
+          const recreated = yield* Effect.gen(function* () {
+            if (!(yield* isStale(lockDir, heartbeatPath, metaPath))) return false
+            yield* forceRemove(lockDir)
+            return yield* atomicMkdir(lockDir)
+          }).pipe(Effect.ensuring(forceRemove(breakerPath)))
+
+          if (!recreated) return yield* new NotAcquired()
+        }
+
+        // We own the lock dir — write heartbeat + meta with exclusive create
+        yield* exclusiveWrite(heartbeatPath, "", lockDir, "heartbeat already existed")
+
+        const metaJson = encodeMeta({ token, pid: process.pid, hostname, createdAt: new Date().toISOString() })
+        yield* exclusiveWrite(metaPath, metaJson, lockDir, "meta.json already existed")
+
+        return { token, metaPath, heartbeatPath, lockDir } satisfies Handle
+      })
+
+      // -- retry wrapper (preserves Handle type) --
+
+      const acquireHandle = (lockfile: string, key: string): Effect.Effect<Handle, LockError> =>
+        tryAcquireLockDir(lockfile).pipe(
+          Effect.retry({
+            while: (err) => err._tag === "NotAcquired",
+            schedule: retrySchedule,
+          }),
+          Effect.catchTag("NotAcquired", () => Effect.fail(new LockTimeoutError({ key }))),
+        )
+
+      // -- release --
+
+      const release = (handle: Handle) =>
+        Effect.gen(function* () {
+          const raw = yield* fs.readFileString(handle.metaPath).pipe(
+            Effect.catch((err) => {
+              if (isPathGone(err)) return Effect.die(new ReleaseError({ detail: "metadata missing" }))
+              return Effect.die(err)
+            }),
+          )
+
+          const parsed = yield* Effect.try({
+            try: () => decodeMeta(raw),
+            catch: (cause) => new ReleaseError({ detail: "metadata invalid", cause }),
+          }).pipe(Effect.orDie)
+
+          if (parsed.token !== handle.token) return yield* Effect.die(new ReleaseError({ detail: "token mismatch" }))
+
+          yield* forceRemove(handle.lockDir)
+        })
+
+      // -- build service --
+
+      const acquire = Effect.fn("EffectFlock.acquire")(function* (key: string, dir?: string) {
+        const lockDir = dir ?? lockRoot
+        yield* ensureDir(lockDir)
+
+        const lockfile = path.join(lockDir, Hash.fast(key) + ".lock")
+
+        // acquireRelease: acquire is uninterruptible, release is guaranteed
+        const handle = yield* Effect.acquireRelease(acquireHandle(lockfile, key), (handle) => release(handle))
+
+        // Heartbeat fiber — scoped, so it's interrupted before release runs
+        yield* fs
+          .utimes(handle.heartbeatPath, new Date(), new Date())
+          .pipe(Effect.ignore, Effect.repeat(Schedule.spaced(HEARTBEAT_MS)), Effect.forkScoped)
+      })
+
+      const withLock: Interface["withLock"] = Function.dual(
+        (args) => Effect.isEffect(args[0]),
+        <A, E, R>(body: Effect.Effect<A, E, R>, key: string, dir?: string): Effect.Effect<A, E | LockError, R> =>
+          Effect.scoped(
+            Effect.gen(function* () {
+              yield* acquire(key, dir)
+              return yield* body
+            }),
+          ),
+      )
+
+      return Service.of({ acquire, withLock })
+    }),
+  )
+
+  export const live = layer.pipe(Layer.provide(AppFileSystem.defaultLayer))
+}
diff --git a/packages/shared/test/fixture/effect-flock-worker.ts b/packages/shared/test/fixture/effect-flock-worker.ts
@@ -0,0 +1,64 @@
+import fs from "fs/promises"
+import path from "path"
+import os from "os"
+import { Effect, Layer } from "effect"
+import { AppFileSystem } from "@opencode-ai/shared/filesystem"
+import { EffectFlock } from "@opencode-ai/shared/util/effect-flock"
+import { Global } from "@opencode-ai/shared/global"
+
+type Msg = {
+  key: string
+  dir: string
+  holdMs?: number
+  ready?: string
+  active?: string
+  done?: string
+}
+
+function sleep(ms: number) {
+  return new Promise<void>((resolve) => setTimeout(resolve, ms))
+}
+
+const msg: Msg = JSON.parse(process.argv[2]!)
+
+const testGlobal = Layer.succeed(
+  Global.Service,
+  Global.Service.of({
+    home: os.homedir(),
+    data: os.tmpdir(),
+    cache: os.tmpdir(),
+    config: os.tmpdir(),
+    state: os.tmpdir(),
+    bin: os.tmpdir(),
+    log: os.tmpdir(),
+  }),
+)
+
+const testLayer = EffectFlock.layer.pipe(Layer.provide(testGlobal), Layer.provide(AppFileSystem.defaultLayer))
+
+async function job() {
+  if (msg.ready) await fs.writeFile(msg.ready, String(process.pid))
+  if (msg.active) await fs.writeFile(msg.active, String(process.pid), { flag: "wx" })
+
+  try {
+    if (msg.holdMs && msg.holdMs > 0) await sleep(msg.holdMs)
+    if (msg.done) await fs.appendFile(msg.done, "1\n")
+  } finally {
+    if (msg.active) await fs.rm(msg.active, { force: true })
+  }
+}
+
+await Effect.runPromise(
+  Effect.gen(function* () {
+    const flock = yield* EffectFlock.Service
+    yield* flock.withLock(
+      Effect.promise(() => job()),
+      msg.key,
+      msg.dir,
+    )
+  }).pipe(Effect.provide(testLayer)),
+).catch((err) => {
+  const text = err instanceof Error ? (err.stack ?? err.message) : String(err)
+  process.stderr.write(text)
+  process.exit(1)
+})
diff --git a/packages/shared/test/util/effect-flock.test.ts b/packages/shared/test/util/effect-flock.test.ts
