Java ExecutorService – invokeAll() vs invokeAny()

 

 

✅ invokeAll(): Wait for All Tasks to Complete

<T> List<Future<T>> invokeAll(Collection<? extends Callable<T>> tasks)

🔹 What it does:

• Submits all tasks at once
• Waits until every task finishes
• Returns a list of Future<T> objects, each representing the result of one task

⏱ With timeout:

invokeAll(tasks, timeout, timeUnit)

• Waits for all tasks, but only within the given time limit

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💡 Example – invokeAll()

ExecutorService executor = Executors.newFixedThreadPool(10);

List<CallableTask> tasks = List.of(
    new CallableTask("task1", 1000),
    new CallableTask("task2", 2000),
    new CallableTask("task3", 3000)
);

List<Future<Integer>> futures = executor.invokeAll(tasks);

for (Future<Integer> future : futures) {
    Integer result = future.get();
    System.out.println("Result: " + result);
}
executor.shutdown();

✅ Output (parallel execution):

task1 running
task2 running
task3 running
task1 done → return 1000
task2 done → return 2000
task3 done → return 3000
Result: 1000
Result: 2000
Result: 3000

🧠 Use invokeAll() when you need all results and are willing to wait.

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✅ invokeAny(): Return First Completed Result

<T> T invokeAny(Collection<? extends Callable<T>> tasks)

🔹 What it does:

• Submits all tasks
• Waits only for the first successful result
• Cancels the remaining tasks

⏱ With timeout:

invokeAny(tasks, timeout, timeUnit)

• Waits for the fastest task to finish within the time limit, otherwise throws TimeoutException

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💡 Example – invokeAny()

ExecutorService executor = Executors.newFixedThreadPool(10);

List<CallableTask> tasks = List.of(
    new CallableTask("task1", 1000),
    new CallableTask("task2", 2000),
    new CallableTask("task3", 3000)
);

Integer result = executor.invokeAny(tasks);
System.out.println("First result: " + result);

executor.shutdown();

✅ Output:

task1 running
task2 running
task3 running
task1 done → return 1000
First result: 1000
task2 interrupted
task3 interrupted

🧠 Use invokeAny() when you only care about the fastest result, and want to save resources by cancelling the others.

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🔄 Summary – invokeAll() vs invokeAny()

Feature invokeAll() invokeAny()

Waits for all tasks	✅ Yes	❌ No – only waits for one
Cancels others	❌ No	✅ Yes – cancels remaining tasks
Return value	List of Future<T>	Single T
Use case	Need all results	Need fastest result