Resources

Resource Management in Effect

Overview

Effect provides structured resource management that guarantees cleanup even when errors occur or the effect is interrupted. This is essential for:

• Database connections
• File handles
• Network sockets
• Locks and semaphores
• Any resource requiring cleanup

Core Concept: Scope

A Scope is a context that tracks resources and ensures their cleanup:

Effect<A, E, R | Scope>;
//              ^^^^^ Indicates resource needs cleanup

Basic Resource Acquisition

Effect.acquireRelease

The fundamental pattern for safe resource management:

import { Effect } from "effect";

const managedFile = Effect.acquireRelease(
  Effect.sync(() => fs.openSync("file.txt", "r")),
  (fd) => Effect.sync(() => fs.closeSync(fd)),
);

Using the Resource

const program = Effect.gen(function* () {
  const fd = yield* managedFile;
  const content = yield* Effect.sync(() => fs.readFileSync(fd, "utf-8"));
  return content;
});

// Run with automatic scope management
const result = yield * Effect.scoped(program);

Effect.scoped

Converts a scoped effect into a regular effect by managing the scope:

const runnable = Effect.scoped(program);

The scope closes when the scoped block completes, triggering all finalizers.

acquireUseRelease Pattern

For simpler cases, combine acquire/use/release in one call:

const readFile = (path: string) =>
  Effect.acquireUseRelease(
    Effect.sync(() => fs.openSync(path, "r")),
    (fd) => Effect.sync(() => fs.readFileSync(fd, "utf-8")),
    (fd) => Effect.sync(() => fs.closeSync(fd)),
  );

Finalizers

Effect.addFinalizer

Add cleanup logic to the current scope:

const program = Effect.gen(function* () {
  yield* Effect.addFinalizer(() => Effect.log("Cleanup running!"));

  // ... do work ...

  return result;
});

Effect.ensuring

Run cleanup after effect completes (success or failure):

const withCleanup = someEffect.pipe(Effect.ensuring(Effect.log("Always runs after effect")));

Effect.onExit

Run different cleanup based on exit status:

const withExitHandler = someEffect.pipe(
  Effect.onExit((exit) => (Exit.isSuccess(exit) ? Effect.log("Succeeded!") : Effect.log("Failed or interrupted"))),
);

Multiple Resources

Sequential Acquisition

const program = Effect.gen(function* () {
  const db = yield* acquireDbConnection;
  const cache = yield* acquireRedisConnection;
});

const result = yield * Effect.scoped(program);

Parallel Acquisition

const program = Effect.gen(function* () {
  const [db, cache] = yield* Effect.all([acquireDbConnection, acquireRedisConnection]);
});

Resource Patterns

Database Connection Pool

const DbPool = Effect.acquireRelease(
  Effect.promise(() =>
    createPool({
      host: "localhost",
      database: "mydb",
      max: 10,
    }),
  ),
  (pool) => Effect.promise(() => pool.end()),
);

const query = (sql: string) =>
  Effect.gen(function* () {
    const pool = yield* DbPool;
    return yield* Effect.tryPromise(() => pool.query(sql));
  });

File Handle

const withFile = <A>(path: string, use: (handle: FileHandle) => Effect.Effect<A>) =>
  Effect.acquireUseRelease(
    Effect.promise(() => fs.promises.open(path)),
    use,
    (handle) => Effect.promise(() => handle.close()),
  );

Lock/Mutex

const withLock = <A>(lock: Lock, effect: Effect.Effect<A>) =>
  Effect.acquireUseRelease(
    lock.acquire,
    () => effect,
    () => lock.release,
  );

Layered Resources

Use Layer.scoped for service-level resources:

const DatabaseLive = Layer.scoped(
  Database,
  Effect.gen(function* () {
    const pool = yield* Effect.acquireRelease(createPool(), (pool) => Effect.promise(() => pool.end()));

    return {
      query: (sql) => Effect.tryPromise(() => pool.query(sql)),
    };
  }),
);

Error Handling in Cleanup

Finalizers should not fail, but if they do:

const safeRelease = (resource: Resource) =>
  Effect.sync(() => resource.close()).pipe(Effect.catchAll((error) => Effect.logError("Cleanup failed", error)));

const managed = Effect.acquireRelease(acquire, safeRelease);

Interruption Safety

Resources are cleaned up even on interruption:

const program = Effect.gen(function* () {
  const resource = yield* acquireResource;

  yield* Effect.sleep("1 hour");
});

const result = yield * program.pipe(Effect.scoped, Effect.timeout("1 second"));

Best Practices

1. Use acquireRelease for paired operations - Guarantees cleanup
2. Keep finalizers simple and infallible - Log errors instead of throwing
3. Use Effect.scoped at appropriate boundaries - Not too wide, not too narrow
4. Clean up in reverse acquisition order - Effect handles this automatically
5. Use Layer.scoped for service-level resources - Lifecycle tied to layer

Additional Resources

For comprehensive resource management documentation, consult ${CLAUDE_PLUGIN_ROOT}/references/llms-full.txt.

Search for these sections:

• "Introduction" (Resource Management) for core concepts
• "Scope" for detailed scope mechanics
• "Managing Layers" for Layer.scoped patterns

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