In ArrayBlockingQueue, inside the put method, why does it call notFull.signal() after catching InterruptedException? When the thread is going to terminate, why does it send out a 'not full' signal?
From the source:
public void put(E e) throws InterruptedException {
if (e == null) throw new NullPointerException();
final E[] items = this.items;
final ReentrantLock lock = this.lock;
lock.lockInterruptibly();
try {
try {
while (count == items.length)
notFull.await();
} catch (InterruptedException ie) {
notFull.signal(); // propagate to non-interrupted thread
throw ie;
}
insert(e);
} finally {
lock.unlock();
}
}
Imagine the following scenario:
Threads 1 and 4 are waiting on notFull, ie, the queue is full, and the lock is released.
Thread 2 holds the lock, and is about to remove an element from the queue.
Thread 3 interrupts Thread 1.
Now imagine the following interleaving:
+-+--+--------+-----------+------- TIME +---+------------+---------------------->
| | | | | | | |
+---------+ +------------------+ +----------+ |
| Thread2 | | Thread2 | | Thread2 | |
| lock() | | notFull.signal() | | unlock() | |
+---------+ +------------------+ +----------+ |
| | | | |
+---------------------+ | | |
| Thread3 | | | |
| Thread1.interrupt() | | | |
+---------------------+ | | |
| | | |
+---------------+ +-------------+ +---------+ +----------------------+
| Thread1 | | Thread1 | | Thread1 | | Thread1 |
| interrupted() | | signalled() | | lock() | | InterruptedException |
+---------------+ +-------------+ +---------+ +----------------------+
What if InterruptedException wasn't caught, and Thread 1 was just to unlock and abandon the wait? What would happen to Thread 4, who was still waiting for a signal on notFull? The signal had already been sent by Thread 2, but it just so happened that the receiving thread, Thread 1, had been interrupted, and the signal was wasted.
In short: If the thread received a signal when it was also interrupted, it passes along the signal to another thread, so that it isn't lost. This prevents threads from waiting indefinitely for something that already happened.
Related
When I trying to use Mockito verify to test extral call times of testMethod(indeed this method is just execute 2 times), but I got following message.
verify(XXXXXXX, times(2)).testMethod(any(XXXXXX.class))
| | | | | |
| | | null null class XXXXXX
| | Wanted invocations count: 2
| Mock for XXXXXXX, hashCode: 292294397
Mock for XXXXXXX, hashCode: 292294397
If I change the times to 1, and the error message is:
verify(XXXXXXX, times(1)).testMethod(any(XXXXXX.class))
| | | | | |
| | | | null class XXX
| | | org.mockito.exceptions.verification.TooManyActualInvocations:
| | | XXX.XXXX(
| | | <any XXX>
| | | );
| | | Wanted 1 time:
| | | -> at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
| | | But was 2 times:
| | | -> at XXXX.XXX(XXX.java:129)
| | | -> at XXXXX.XXX(XXX.java:129)
| | |
| | |
| | Wanted invocations count: 1
Does anybody have met this problem before?
Single-job schedule with two vehicles. One vehicle starts close to the job, the other starts far from the job. Seems it should prefer to use the closer vehicle, as there's a cost-per-distance. But it uses the farther one, if there's a non-zero setCostPerWaitingTime(). Why?
public void testUseCloserVehicleWhenCostsAreSet() throws Exception {
VehicleType type = VehicleTypeImpl.Builder.newInstance("generic")
.setCostPerDistance(0.017753)
//.setCostPerTransportTime(1.0)
.setCostPerWaitingTime(1.0)
.build();
double serviceTime = 420.0;
Location pointA = Location.newInstance(100.0, 100.0);
Location pointB = Location.newInstance(100.0, 200.0);
Location closeToPointA = Location.newInstance(110.0, 110.0);
Location farFromPointA = Location.newInstance(500.0, 110.0);
VehicleRoutingProblem vrp = VehicleRoutingProblem.Builder
.newInstance()
.setFleetSize(VehicleRoutingProblem.FleetSize.FINITE)
.addVehicle(VehicleImpl.Builder.newInstance("CloseBy")
.setType(type)
.setStartLocation(closeToPointA)
.build())
.addVehicle(VehicleImpl.Builder.newInstance("FarAway")
.setType(type)
.setStartLocation(farFromPointA)
.build())
.addJob(Shipment.Builder.newInstance("123")
.setPickupLocation(pointA)
.setPickupServiceTime(serviceTime)
.setDeliveryLocation(pointB)
.setDeliveryServiceTime(serviceTime)
.setPickupTimeWindow(new TimeWindow(36000.0, 36360.0))
.setDeliveryTimeWindow(new TimeWindow(36360.0, 36720.0))
.setMaxTimeInVehicle(720.0)
.build())
.build();
VehicleRoutingAlgorithm algorithm = Jsprit.Builder.newInstance(vrp)
.buildAlgorithm();
VehicleRoutingProblemSolution bestSolution = Solutions.bestOf(algorithm.searchSolutions());
SolutionPrinterWithTimes.print(vrp, bestSolution, SolutionPrinterWithTimes.Print.VERBOSE);
System.out.flush();
assertEquals("CloseBy", bestSolution.getRoutes().iterator().next().getVehicle().getId());
}
Result:
+----------------------------------------------------------+
| solution |
+---------------+------------------------------------------+
| indicator | value |
+---------------+------------------------------------------+
| costs | 35616.03246830352 |
| noVehicles | 1 |
| unassgndJobs | 0 |
+----------------------------------------------------------+
+--------------------------------------------------------------------------------------------------------------------------------+
| detailed solution |
+---------+----------------------+-----------------------+-----------------+-----------------+-----------------+-----------------+
| route | vehicle | activity | job | arrTime | endTime | costs |
+---------+----------------------+-----------------------+-----------------+-----------------+-----------------+-----------------+
| 1 | FarAway | start | - | undef | 0 | 0 |
| 1 | FarAway | pickupShipment | 123 | 400 | 36420 | 35607 |
| 1 | FarAway | deliverShipment | 123 | 36520 | 36940 | 35609 |
| 1 | FarAway | end | - | 37350 | undef | 35616 |
+--------------------------------------------------------------------------------------------------------------------------------+
junit.framework.ComparisonFailure:
Expected :CloseBy
Actual :FarAway
I suspect it has something to do with the vehicle arriving at 400 for a job that can't start until 36000. Is there a way to prevent that, so the vehicle starts only as early as needed to reach the first job? Does setCostPerWaitingTime do something other than what I think?
Here's a comparison of the job with only the CloseBy vehicle.
+--------------------------------------------------------------------------------------------------------------------------------+
| detailed solution |
+---------+----------------------+-----------------------+-----------------+-----------------+-----------------+-----------------+
| route | vehicle | activity | job | arrTime | endTime | costs |
+---------+----------------------+-----------------------+-----------------+-----------------+-----------------+-----------------+
| 1 | FarAway | start | - | undef | 0 | 0 |
| 1 | FarAway | pickupShipment | 123 | 400 | 36420 | 35607 |
| 1 | FarAway | deliverShipment | 123 | 36520 | 36940 | 35609 |
| 1 | FarAway | end | - | 37350 | undef | 35616 |
+--------------------------------------------------------------------------------------------------------------------------------+
+--------------------------------------------------------------------------------------------------------------------------------+
| detailed solution |
+---------+----------------------+-----------------------+-----------------+-----------------+-----------------+-----------------+
| route | vehicle | activity | job | arrTime | endTime | costs |
+---------+----------------------+-----------------------+-----------------+-----------------+-----------------+-----------------+
| 1 | CloseBy | start | - | undef | 0 | 0 |
| 1 | CloseBy | pickupShipment | 123 | 14 | 36420 | 35986 |
| 1 | CloseBy | deliverShipment | 123 | 36520 | 36940 | 35988 |
| 1 | CloseBy | end | - | 37031 | undef | 35989 |
+--------------------------------------------------------------------------------------------------------------------------------+
I think the problem is that the CloseBy vehicle arrives sooner, so it pays higher wait costs, while the other vehicle is driving during that time so pays less in wait costs. This would be mitigated if the vehicle didn't start until it needed to, but I'm unsure how to set that up.
I have setup where multiple servers run a #Schedule which run a spring batch job that sends out emails to users. I want to make sure that only one instance of this job is ran across multiple servers.
Based on this question
I have implemented some logic to see if its possible to solve this using only spring batch.
To run a job I created a helper class JobRunner with the following methods:
public void run(Job job) {
try {
jobLauncher.run(job, new JobParameters());
} catch (JobExecutionAlreadyRunningException e) {
// Check if job is inactive and stop it if so.
stopIfInactive(job);
} catch (JobExecutionException e) {
...
}
}
The stopIfInactive method:
private void stopIfInactive(Job job) {
for (JobExecution execution : jobExplorer.findRunningJobExecutions(job.getName())) {
Date createTime = execution.getCreateTime();
DateTime now = DateTime.now();
// Get running seconds for more info.
int seconds = Seconds
.secondsBetween(new DateTime(createTime), now)
.getSeconds();
LOGGER.debug("Job '{}' already has an execution with id: {} with age of {}s",
job.getName(), execution.getId(), seconds);
// If job start time exceeds the execution window, stop the job.
if (createTime.before(now.minusMillis(EXECUTION_DEAD_MILLIS)
.toDate())) {
LOGGER.warn("Execution with id: {} is inactive, stopping",
execution.getId());
execution.setExitStatus(new ExitStatus(BatchStatus.FAILED.name(),
String.format("Stopped due to being inactive for %d seconds", seconds)));
execution.setStatus(BatchStatus.FAILED);
execution.setEndTime(now.toDate());
jobRepository.update(execution);
}
}
}
And then the jobs are ran by the following on all servers:
#Scheduled(cron = "${email.cron}")
public void sendEmails() {
jobRunner.run(emailJob);
}
Is this a valid solution for a multiple server setup? If not, what are the alternatives?
EDIT 1
I've did a bit more testing - setup two applications which run a #Schedule every 5 seconds that initiates a job using the helper class I created. It seems that my solution does not resolve the problem. Here is the data from batch_job_execution table that is used by spring batch:
job_execution_id | version | job_instance_id | create_time | start_time | end_time | status | exit_code | exit_message | last_updated | job_configuration_location
------------------+---------+-----------------+-------------------------+-------------------------+-------------------------+-----------+-----------+--------------+-------------------------+----------------------------
1007 | 2 | 2 | 2016-08-25 14:43:15.024 | 2016-08-25 14:43:15.028 | 2016-08-25 14:43:16.84 | COMPLETED | COMPLETED | | 2016-08-25 14:43:16.84 |
1006 | 1 | 2 | 2016-08-25 14:43:15.021 | 2016-08-25 14:43:15.025 | | STARTED | UNKNOWN | | 2016-08-25 14:43:15.025 |
1005 | 2 | 2 | 2016-08-25 14:43:10.326 | 2016-08-25 14:43:10.329 | 2016-08-25 14:43:12.047 | COMPLETED | COMPLETED | | 2016-08-25 14:43:12.047 |
1004 | 2 | 2 | 2016-08-25 14:43:10.317 | 2016-08-25 14:43:10.319 | 2016-08-25 14:43:12.03 | COMPLETED | COMPLETED | | 2016-08-25 14:43:12.03 |
1003 | 2 | 2 | 2016-08-25 14:43:05.017 | 2016-08-25 14:43:05.02 | 2016-08-25 14:43:06.819 | COMPLETED | COMPLETED | | 2016-08-25 14:43:06.819 |
1002 | 2 | 2 | 2016-08-25 14:43:05.016 | 2016-08-25 14:43:05.018 | 2016-08-25 14:43:06.811 | COMPLETED | COMPLETED | | 2016-08-25 14:43:06.811 |
1001 | 2 | 2 | 2016-08-25 14:43:00.038 | 2016-08-25 14:43:00.042 | 2016-08-25 14:43:01.944 | COMPLETED | COMPLETED | | 2016-08-25 14:43:01.944 |
1000 | 2 | 2 | 2016-08-25 14:43:00.038 | 2016-08-25 14:43:00.041 | 2016-08-25 14:43:01.922 | COMPLETED | COMPLETED | | 2016-08-25 14:43:01.922 |
999 | 2 | 2 | 2016-08-25 14:42:55.02 | 2016-08-25 14:42:55.024 | 2016-08-25 14:42:57.603 | COMPLETED | COMPLETED | | 2016-08-25 14:42:57.603 |
998 | 2 | 2 | 2016-08-25 14:42:55.02 | 2016-08-25 14:42:55.023 | 2016-08-25 14:42:57.559 | COMPLETED | COMPLETED | | 2016-08-25 14:42:57.559 |
(10 rows)
I also tried the method provided by #Palcente, I've got similar results.
Spring Integration's latest release added some functionality around distributed locks. This is really what you'd want to use to make sure that only one server fires the job (only the server that obtains the lock should launch the job). You can read more about Spring Integration's locking capabilities in the documentation here: http://projects.spring.io/spring-integration/
I am working on a Sequence diagram, but I am confused on how to show the following bit of sequence diagram.
I am trying to instantiate a variable by first calling a function to get the variable type. I already have made myMainObject. So that object exists and I understand I have to do a create on something when I instantiate it.
myMainObject().getObjectController().getObject();
So does this mean I create ObjectController AND I also create Object lifelines?
--------------
| myMainObject |
-------------
|
| getObjectcontroller() -----------------
| ----------------------->| ObjectController|
| ------------------
| | getObject() ---------
| |--------------------->| Object |
| | ---------
| | |
|
Or is the following more than enough information? And let the programmer figure out on how to get the correct object.
--------------------------
| myMainObject: MainObject|
-------------------------
|
| myObject = getObject() ---------
| ----------------------->| Object |
| ---------
| |
| |
| |
| |
ObjectController doesn't call Object. You call both methods.
-----
| You |
-----
|
| getObjectcontroller() -------------
| ----------------------> | MainObject |
| -------------
| Objectcontroller |
| <----------------------------- |
| |
|
| getObject() ------------------
| ---------------------------------------> | Objectcontroller |
| ------------------
| Object |
| <------------------------------------------------ |
| |
I want automatically answer all sip calls.
When I respond with trying or ringing, the transaction is in a proceeding state,
but when I send the OK response, the transaction is in a terminated state.
This is my code:
public void processRequest(RequestEvent requestReceivedEvent)
{
Address contactAddress = myAddressFactory.createAddress("sip:" + myIP + ":" + myPort);
myContactHeader = myHeaderFactory.createContactHeader(contactAddress);
Request req = requestReceivedEvent.getRequest();
myGUI.display("<<< " + req.toString());
String method = req.getMethod(); //bad request type.
FromHeader from = (FromHeader) req.getHeader("From");
Response response = null;
try
{ //Reply with OK
response = myMessageFactory.createResponse(200, req);
ToHeader toHeader = (ToHeader) response.getHeader(ToHeader.NAME);
toHeader.setTag("888"); //Identifier, specific to your application
ServerTransaction st = mySipProvider.getNewServerTransaction(req);
response.addHeader(myContactHeader);
st.sendResponse(response);
System.out.println("Ok response: " + st.getState());
}
catch (Exception e)
{
e.printStackTrace();
}
}
Thanks in advance.
INVITE server transactions to go terminated state after 200 OK. It's normal. Your call is answered and you shouldn't worry about it.
(see diagram of state machine from RFC)
|INVITE
|pass INV to TU
INVITE V send 100 if TU won't in 200ms
send response+-----------+
+--------| |--------+101-199 from TU
| | Proceeding| |send response
+------->| |<-------+
| | Transport Err.
| | Inform TU
| |--------------->+
+-----------+ |
300-699 from TU | |2xx from TU |
send response | |send response |
| +------------------>+
| |
INVITE V Timer G fires |
send response+-----------+ send response |
+--------| |--------+ |
| | Completed | | |
+------->| |<-------+ |
+-----------+ |
| | |
ACK | | |
- | +------------------>+
| Timer H fires |
V or Transport Err.|
+-----------+ Inform TU |
| | |
| Confirmed | |
| | |
+-----------+ |
| |
|Timer I fires |
|- |
| |
V |
+-----------+ |
| | |
| Terminated|<---------------+
| |
+-----------+
Figure 7: INVITE server transaction