fix: dispose stale tasks (#2)

src/async-seq.ts

@@ -98,18 +98,24 @@ export class AsyncSeq {
     let fn: AsyncSeqFn | undefined;
     while ((fn = this.#fns[0])) {
       if (this.#disposer) {
-        await tryCall(this.#disposer);
+        tryCall(this.#disposer);
+        this.#disposer = null;
       }
       const disposer = await tryCall(fn);
-      this.#disposer = disposer;
-      if (isAbortable(disposer)) {
-        disposer.abortable(() => {
-          if (this.#disposer === disposer) {
-            this.#disposer = null;
-          }
-        });
+      if (fn === this.#fns[0]) {
+        this.#disposer = disposer;
+        if (isAbortable(disposer)) {
+          disposer.abortable(() => {
+            if (this.#disposer === disposer) {
+              this.#disposer = null;
+            }
+          });
+        }
+        this.#fns.shift();
+      } else {
+        // stale task
+        disposer?.();
       }
-      this.#fns.shift();
     }
     this.#pRunning = null;
   }

test/async-seq.test.ts

@@ -61,6 +61,57 @@ it("should drop item from the tail if the sequence is full", async () => {
   }
 });
 
+it("should drop item from the tail when adding to a sequence", async () => {
+  const window = 3;
+  const s = seq({ window });
+
+  const disposers2 = Array.from({ length: 10 }).map(() => vi.fn());
+  const spies2 = Array.from({ length: 10 }).map((_, i) =>
+    vi.fn(async () => {
+      await new Promise(resolve => setTimeout(resolve, 100));
+      return disposers2[i];
+    })
+  );
+
+  const disposers1 = Array.from({ length: 3 }).map(() => vi.fn());
+  const spies1 = Array.from({ length: 3 }).map((_, i) =>
+    vi.fn(async () => {
+      if (i === 1) {
+        s.add(...spies2);
+      }
+      await new Promise(resolve => setTimeout(resolve, 100));
+      return disposers1[i];
+    })
+  );
+
+  const p = s.add(...spies1);
+  expect(s.size).toBe(window);
+  expect(s.full).toBe(true);
+  expect(s.running).toBe(true);
+
+  await p;
+  expect(s.size).toBe(0);
+  expect(s.full).toBe(false);
+  expect(s.running).toBe(false);
+
+  for (const [i, spy] of spies1.entries()) {
+    expect(spy, `spy${i}`).toBeCalledTimes(1);
+  }
+
+  for (const [i, disposer] of disposers1.entries()) {
+    expect(disposer, `disposer${i}`).toBeCalledTimes(1);
+  }
+
+  for (const [i, spy] of spies2.entries()) {
+    expect(spy, `spy${i}`).toBeCalledTimes(i === 0 ? 1 : 0);
+  }
+
+  await s.dispose();
+  for (const [i, disposer] of disposers2.entries()) {
+    expect(disposer, `disposer${i}`).toBeCalledTimes(i === 0 ? 1 : 0);
+  }
+});
+
 it("should wait for the sequence to finish", async () => {
   const s = seq();
   const spy = vi.fn(async () => {
@@ -97,6 +148,65 @@ it("should drop item from the head if the sequence is full", async () => {
   }
 });
 
+it("should drop item from the head when adding to a sequence", async () => {
+  const window = 3;
+  const s = seq({ window, dropHead: true });
+  const disposers2 = Array.from({ length: 10 }).map(() => vi.fn());
+  const spies2 = Array.from({ length: 10 }).map((_, i) =>
+    vi.fn(async () => {
+      await new Promise(resolve => setTimeout(resolve, 100));
+      return disposers2[i];
+    })
+  );
+  const disposers1 = Array.from({ length: 3 }).map(() => vi.fn());
+  const spies1 = Array.from({ length: 3 }).map((_, i) =>
+    vi.fn(async () => {
+      if (i === 1) {
+        s.add(...spies2);
+      }
+      await new Promise(resolve => setTimeout(resolve, 100));
+      return disposers1[i];
+    })
+  );
+
+  const p = s.add(...spies1);
+  expect(s.size).toBe(window);
+  expect(s.full).toBe(true);
+  expect(s.running).toBe(true);
+
+  await p;
+  expect(s.size).toBe(0);
+  expect(s.full).toBe(false);
+  expect(s.running).toBe(false);
+
+  for (const [i, spy] of spies1.entries()) {
+    expect(spy, `spy${i} of 0-${spies1.length - 1}`).toBeCalledTimes(
+      i <= 1 ? 1 : 0
+    );
+  }
+
+  for (const [i, disposer] of disposers1.entries()) {
+    expect(
+      disposer,
+      `disposer${i} of 0-${disposers1.length - 1}`
+    ).toBeCalledTimes(i <= 1 ? 1 : 0);
+  }
+
+  for (const [i, spy] of spies2.entries()) {
+    expect(spy, `spy${i} of 0-${spies2.length - 1}`).toBeCalledTimes(
+      i >= spies2.length - 3 ? 1 : 0
+    );
+  }
+
+  await s.dispose();
+  for (const [i, disposer] of disposers2.entries()) {
+    expect(
+      disposer,
+      `disposer${i} of 0-${disposers2.length - 1}`
+    ).toBeCalledTimes(i >= spies2.length - 3 ? 1 : 0);
+  }
+});
+
 it("should catch error in tasks", async () => {
   const spy = vi
     .spyOn(globalThis.console, "error")