add Effect.Semaphore.resize (#5295)

Author: tim-smart

.changeset/icy-walls-make.md

@@ -0,0 +1,5 @@
+---
+"effect": minor
+---
+
+add Effect.Semaphore.resize

packages/effect/src/Effect.ts

@@ -11770,6 +11770,11 @@ export interface Permit {
  * @since 2.0.0
  */
 export interface Semaphore {
+  /**
+   * Adjusts the number of permits available in the semaphore.
+   */
+  resize(permits: number): Effect<void>
+
   /**
    * Runs an effect with the given number of permits and releases the permits
    * when the effect completes.

packages/effect/src/internal/effect/circular.ts

@@ -37,7 +37,7 @@ class Semaphore {
   public waiters = new Set<() => void>()
   public taken = 0
 
-  constructor(readonly permits: number) {}
+  constructor(public permits: number) {}
 
   get free() {
     return this.permits - this.taken
@@ -63,21 +63,35 @@ class Semaphore {
       return resume(core.succeed(n))
     })
 
-  readonly updateTaken = (f: (n: number) => number): Effect.Effect<number> =>
-    core.withFiberRuntime((fiber) => {
-      this.taken = f(this.taken)
-      if (this.waiters.size > 0) {
-        fiber.getFiberRef(currentScheduler).scheduleTask(() => {
-          const iter = this.waiters.values()
-          let item = iter.next()
-          while (item.done === false && this.free > 0) {
-            item.value()
-            item = iter.next()
-          }
-        }, fiber.getFiberRef(core.currentSchedulingPriority))
-      }
-      return core.succeed(this.free)
-    })
+  updateTakenUnsafe(fiber: Fiber.RuntimeFiber<any, any>, f: (n: number) => number): Effect.Effect<number> {
+    this.taken = f(this.taken)
+    if (this.waiters.size > 0) {
+      fiber.getFiberRef(currentScheduler).scheduleTask(() => {
+        const iter = this.waiters.values()
+        let item = iter.next()
+        while (item.done === false && this.free > 0) {
+          item.value()
+          item = iter.next()
+        }
+      }, fiber.getFiberRef(core.currentSchedulingPriority))
+    }
+    return core.succeed(this.free)
+  }
+
+  updateTaken(f: (n: number) => number): Effect.Effect<number> {
+    return core.withFiberRuntime((fiber) => this.updateTakenUnsafe(fiber, f))
+  }
+
+  readonly resize = (permits: number) =>
+    core.asVoid(
+      core.withFiberRuntime((fiber) => {
+        this.permits = permits
+        if (this.free < 0) {
+          return core.void
+        }
+        return this.updateTakenUnsafe(fiber, (taken) => taken)
+      })
+    )
 
   readonly release = (n: number): Effect.Effect<number> => this.updateTaken((taken) => taken - n)
 
@@ -104,7 +118,7 @@ class Semaphore {
 }
 
 /** @internal */
-export const unsafeMakeSemaphore = (permits: number): Semaphore => new Semaphore(permits)
+export const unsafeMakeSemaphore = (permits: number): Effect.Semaphore => new Semaphore(permits)
 
 /** @internal */
 export const makeSemaphore = (permits: number) => core.sync(() => unsafeMakeSemaphore(permits))

packages/effect/test/Effect/semaphore.test.ts

@@ -1,4 +1,4 @@
-import { describe, it } from "@effect/vitest"
+import { assert, describe, it } from "@effect/vitest"
 import { strictEqual } from "@effect/vitest/utils"
 import * as D from "effect/Duration"
 import * as Effect from "effect/Effect"
@@ -35,9 +35,25 @@ describe("Effect", () => {
 
   it.effect("releaseAll", () =>
     Effect.gen(function*() {
-      const sem = yield* (Effect.makeSemaphore(4))
-      yield* (sem.take(4))
-      yield* (sem.releaseAll)
-      yield* (sem.take(1))
+      const sem = yield* Effect.makeSemaphore(4)
+      yield* sem.take(4)
+      yield* sem.releaseAll
+      yield* sem.take(1)
+    }))
+
+  it.effect("resize", () =>
+    Effect.gen(function*() {
+      const sem = yield* Effect.makeSemaphore(4)
+      yield* sem.take(4)
+      yield* sem.resize(2)
+      const fiber = yield* Effect.fork(sem.take(1))
+      yield* TestClock.adjust(1)
+      assert.isNull(fiber.unsafePoll())
+      yield* sem.release(2)
+      yield* TestClock.adjust(1)
+      assert.isNull(fiber.unsafePoll())
+      yield* sem.release(1)
+      yield* TestClock.adjust(1)
+      assert.isTrue(fiber.unsafePoll() !== null)
     }))
 })