Termination

Terminating scripts that run out of control is quite important in terms of protecting the applications from being attacked by malicious scripts. In Javet, there are 2 typical ways of terminating scripts.

Automatic Termination with Pool and Engine

IJavetEngineGuard is the built-in support for terminating a script which runs out of control.

// Get an engine from the pool as usual.
try (IJavetEngine iJavetEngine = iJavetEnginePool.getEngine()) {
    V8Runtime v8Runtime = iJavetEngine.getV8Runtime();
    // Get a guard from the engine and apply try-with-resource pattern.
    try (IJavetEngineGuard iJavetEngineGuard = iJavetEngine.getGuard(10000)) {
        v8Runtime.getExecutor("while (true) {}").executeVoid();
        // That infinite loop will be terminated in 10 seconds by the guard.
    } catch (JavetTerminatedException e) {
        // JavetTerminatedException will be thrown to mark that.
        assertFalse(e.isContinuable());
    }
    assertEquals(2, v8Runtime.getExecutor("1 + 1").executeInteger(),
            "The V8 runtime is not dead and is still able to execute code afterwards.");
}

Does IJavetEngineGuard hang normal scripts till timeout is hit? No, it doesn't cause any overhead. If the script completes, IJavetEngineGuard.close() will be called via try-with-resource pattern and cancel the daemon thread immediately.

Please refer to the source code for more detail.

Manual Termination

Manual termination gives applications complete control. In return, the coding effort is considerable.

V8Host v8Host = V8Host.getV8Instance();
try (V8Runtime v8Runtime = v8Host.createV8Runtime()) {
    // Create a daemon thread monitoring the V8 runtime status.
    Thread daemonThread = new Thread(() -> {
        // V8 runtime isInUse() does not require lock.
        while (!v8Runtime.isInUse()) {
            try {
                TimeUnit.MILLISECONDS.sleep(1);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
        // V8 runtime terminateExecution() does not require lock.
        v8Runtime.terminateExecution();
    });
    daemonThread.start();
    try {
        v8Runtime.getExecutor(
                "var count = 0; while (true) { ++count; }")
                .executeVoid();
        fail("Failed to throw exception when execution is terminated.");
    } catch (JavetTerminatedException e) {
        assertFalse(e.isContinuable());
    }
    final int count = v8Runtime.getGlobalObject().getInteger("count");
    assertTrue(count > 0, "Count should be greater than 0.");
    assertEquals(2, v8Runtime.getExecutor("1 + 1").executeInteger(),
            "V8 runtime should still be able to execute script after being terminated.");
}

How about Debug Mode?

Usually, when application is being debugged, JavetEngineGuard may easily interrupt the debug. No worry, JavetEngineGuard is by default disabled in debug mode. Please refer to disableInDebugMode() and enableInDebugMode() for detail.