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ant/tests/test_async_iterable_stream_cleanup.cjs
457d5953e6c8master

test_async_iterable_stream_cleanup.cjs
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			function assert(condition, message) {
			if (!condition) throw new Error(message);
			}

			function assertEq(actual, expected, message) {
			if (actual !== expected) {
			throw new Error(`${message}: expected ${expected}, got ${actual}`);
			}
			}

			function createAsyncIterableStream(source, trace) {
			const stream = source.pipeThrough(new TransformStream());

			stream[Symbol.asyncIterator] = function() {
			const reader = this.getReader();
			let finished = false;

			async function cleanup(cancelStream) {
			if (finished) return;
			finished = true;

			try {
			if (cancelStream) {
			trace.push('cleanup-before-cancel');
			await reader.cancel();
			trace.push('cleanup-after-cancel');
			}
			} finally {
			trace.push('cleanup-before-releaseLock');
			reader.releaseLock();
			trace.push('cleanup-after-releaseLock');
			}
			}

			return {
			async next() {
			const result = await reader.read();
			if (result.done) {
			await cleanup(false);
			return { done: true, value: void 0 };
			}

			trace.push(`next:${result.value}`);
			return { done: false, value: result.value };
			},

			async return() {
			trace.push('return-start');
			await cleanup(true);
			trace.push('return-end');
			return { done: true, value: void 0 };
			},
			};
			};

			return stream;
			}

			async function main() {
			const trace = [];
			const source = new ReadableStream({
			start(controller) {
			controller.enqueue('alpha');
			controller.enqueue('beta');
			controller.close();
			},
			cancel() {
			trace.push('source-cancel');
			},
			});

			const stream = createAsyncIterableStream(source, trace);

			assert(typeof stream[Symbol.asyncIterator] === 'function', 'stream should expose @@asyncIterator');

			for await (const chunk of stream) {
			trace.push(`chunk:${chunk}`);
			break;
			}

			trace.push('loop-exit');

			assertEq(
			trace.join(','),
			[
			'next:alpha',
			'chunk:alpha',
			'return-start',
			'cleanup-before-cancel',
			'cleanup-after-cancel',
			'cleanup-before-releaseLock',
			'cleanup-after-releaseLock',
			'return-end',
			'loop-exit',
			].join(','),
			'for-await cleanup should finish after cancel/releaseLock'
			);

			console.log('async iterable stream cleanup survives cancel/releaseLock');
			}

			main().catch((err) => {
			console.error(err && err.stack ? err.stack : String(err));
			throw err;
			});

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