fiber parking or parked has no chance to to call `park`

[smallnest]

I write a program that queries memcached and sends a lot of http requests to CDN servers. I use comsat http client to send http requests. When I test its performance, AssertionError was thrown (quasar is 0.7.6, comsat-httpclient-0.7.0.jar):

Exception in Fiber "fiber-10002608" java.lang.AssertionError: Unexpected task state (fiber parking or parked has no chance to to call `park`): -2
    at co.paralleluniverse.concurrent.forkjoin.ParkableForkJoinTask.park(ParkableForkJoinTask.java:223)
    at co.paralleluniverse.fibers.FiberForkJoinScheduler$FiberForkJoinTask.park(FiberForkJoinScheduler.java:288)
    at co.paralleluniverse.fibers.Fiber.park1(Fiber.java:707)
    at co.paralleluniverse.fibers.Fiber.park(Fiber.java:620)
    at co.paralleluniverse.fibers.Fiber.park(Fiber.java:624)
    at co.paralleluniverse.fibers.FiberAsync.run(FiberAsync.java:121)
    at co.paralleluniverse.fibers.httpclient.AsyncHttpReq.run(AsyncHttpReq.java:26)
    at co.paralleluniverse.fibers.httpclient.FiberHttpClient.doExecute(FiberHttpClient.java:96)
    at co.paralleluniverse.fibers.httpclient.FiberHttpClient.execute(FiberHttpClient.java:161)
    at co.paralleluniverse.fibers.httpclient.FiberHttpClient.execute(FiberHttpClient.java:190)
    at com.abc.common.util.HttpUtil.getLocationByHttpHEAD(HttpUtil.java:549)
    at com.abc.mgt.ContentRouterProxy.callCCRForClientEdgeCache(ContentRouterProxy.java:388)
    at co.paralleluniverse.strands.SuspendableUtils$VoidSuspendableCallable.run(SuspendableUtils.java:44)
    at co.paralleluniverse.strands.SuspendableUtils$VoidSuspendableCallable.run(SuspendableUtils.java:32)
    at co.paralleluniverse.fibers.Fiber.run(Fiber.java:1072)

My question is why this exception was thrown and how to fix it? I can't find any document to avoid it.

[pron]

Can you share your code?

[smallnest]

It is a complex system that I try to replace threads with fibers and it has too many dependencies. I can exact the major biz logic as this:

            new Fiber<Void>(new SuspendableRunnable() {
                public void run() throws SuspendExecution, InterruptedException {
                    try {
                        c1.m1();
                    } catch (Exception ex) {

                    }
                }
            }).start();

            Class c1:

            @Suspendable
            pubic void m1() {
                //do something
                c2.m2()
                //do something
            }

            Class c2:
            @Suspendable
            pubic void m2() {
                //do something
                c3.m3()
                //do something
            }

            Class c3:
            @Suspendable
            pubic void m3() {
                //do something
                c4.m4()
                //do something
            }

            Class c4:
            @Suspendable
            pubic void m4() {
                //do something
                c5.m5()
                //do something
            }

            Class c5:
            @Suspendable
            pubic void m5() {
                //do something
                contentRouterProxy.m6()
                //do something
            }

            Class contentRouterProxy:
            @Suspendable
            pubic void m6() {
                //do something
                HttpUtil.getLocationByHttpHEAD()
                //do something
            }

            class HttpUtil:

            @Suspendable
            public static void getLocationByHttpHEAD(......)
                String location = ......

                for(int i = 0; i < maxRedirectLoopStatic; i++){
                    HttpUriRequest httpRequest = new HttpHead(location);
                    httpRequest.setHeader("Connection", "keep-alive");
                    CloseableHttpResponse response = client.execute(httpRequest);
                    //EntityUtils.toString(response.getEntity(), Charset.forName("utf-8"));
                    response.close();

                    if (response.getStatusLine().getStatusCode() /100 = 3) {
                        location = getLocation(response)
                        continue
                    }

                    return

                }
                .....
            }

            public static RequestConfig requestConfig = RequestConfig.custom()
            .setSocketTimeout(1000)
            .setConnectTimeout(1000)
            .setConnectionRequestTimeout(1000)
            .setRedirectsEnabled(false)
            .build();

            public static CloseableHttpClient client = FiberHttpClientBuilder.
            create(Runtime.getRuntime().availableProcessors()). // use 2 io threads
            setDefaultRequestConfig(requestConfig).
            disableConnectionState().
            setMaxConnPerRoute(20000).
            setMaxConnTotal(20000).build();

Basically a fiber runs nested methods and the last method uses comsat-httpclient to do redirection manually.

There are a lot of requests at that moment.

[smallnest]

Is one fiber parked more than once? At the first the fiber state is changed from RUNNABLE to PARKING, At that moment the fiber is parked again.

[pron]

Is one fiber parked more than once?

It appears that way from the exception, but I have a hard time seeing how this could happen. If you don't mind sharing your code, you can upload it here or send it to me personally (ron [at] ourdomain)