I have a webserver that has a serverside handler per HTTP-GET and path.
The return-value of the handler-function is the HTTP-response.
E.g.
String handleGetList (Params ps)
{
String str = "<ul>";
// ...
str += "</ul>";
retrun str;
}
Now think of a handler that should execute an axtion that terminates the server (e.g. shutdown, stop HTTP-server, ...).
How can I do so to have the action and also the response??
String handleTerminate (Params ps)
{
system ("shutdown");
retrun "OK";
}
Shutdown before return would not send the response.
Response before shutdown would not executes the shutdown.
How to get both?
Sure I can set a marker for some external app that does the shutdown after the response is sent but maybe there is an easier way.
I did it now this way.
handler ()
{
system ("sleep 3 && shutdown &");
print "OK";
}
Because of & the system does not wait till it ends and with the sleep the whole handler can finish before the shutdown happens.
Related
I have an api call that I want to kick off a long running job and then return a 200 ok. Currently it will kick of the job and move on, but once the initial function finishes what it needs to do, it still seems to wait until the coroutine has finished. I'm sure this is related to my relatively new understanding of kotlin coroutines.
fun apiCall() {
log.info("started")
longJob()
log.info("finished")
return ResponseEntity.ok()
}
fun longJob() {
runBlocking{
launch {
do stufff...
}
}
}
So basically I'm expected to see the logs print and then kick off the longJob and then see 200 in postman. But I'm actually getting both logs printed out as well as the job kicked off, but I don't see my 200ok until the job finishes.
If I understand correctly, you want to launch the longJob in background, and return 200ok status without waiting for longJob to finish. If this is the case then you can't use runBlocking here, it blocks the current thread until all jobs, launched in it, finish. You can create a CoroutineScope and launch and forget a long running task. The sample code:
val scope = CoroutineScope(Dispatchers.IO) // or CoroutineScope(Dispatchers.IO + SupervisorJob())
fun apiCall() {
log.info("started")
scope.launch { longJob() }
log.info("finished")
return ResponseEntity.ok()
}
In this sample logs "started" and "finished" will be printed before longJob() starts executing.
I am using Masstransit with RabbitMQ. As part of some deployment procedure, At some point in time I need my service to disconnect and stop receiving any messages.
Assuming that I won't need the bus until the next restart of the service, will it be Ok to use bus.StopAsync()?
Is there a way to get list of end points and then remove them from listining ?
You should StopAsync the bus, and then when ready, call StartAsync to bring it back up (or start it at the next service restart).
To stop receiving messages without stopping the buss I needed a solution that will avoid the consume message pipeline from consuming any type of message. I tried with observers but unsuccessfully. My solution came up with custom consuming message filter.
The filter part looks like this
public class ComsumersBlockingFilter<T> :
IFilter<ConsumeContext<T>>
where T : class
{
public void Probe(ProbeContext context)
{
var scope = context.CreateFilterScope("messageFilter");
}
public async Task Send(ConsumeContext<T> context, IPipe<ConsumeContext<T>> next)
{
// Check if the service is degraded (true for this demo)
var isServiceDegraded = true;
if (isServiceDegraded)
{
//Suspend the message for 5 seconds
await Task.Delay(TimeSpan.FromMilliseconds(5000), context.CancellationToken);
if (!context.CancellationToken.IsCancellationRequested)
{
//republish the message
await context.Publish(context.Message);
Console.WriteLine($"Message {context.MessageId} has been republished");
}
// NotifyConsumed to avoid skipped message
await context.NotifyConsumed(TimeSpan.Zero, "messageFilter");
}
else
{
//Next filter in the pipe is called
await next.Send(context);
}
}
}
The main idea is to delay with cancellation token and the republish the message. After that call contect.NotifyConsumed to avoid the next pipeline filters and return normally.
I have implemented my own partition assignment strategy by implementing RangeAssignor in my spring boot application.
I have overridden its subscriptionUserData method and adding some user data. Whenever this data is getting changed I want to trigger partition rebalance by invoking below kafkaConsumer's api
kafkaconsumer apis enforce rebalance
I am not sure how can I get the object of kafka consumer and invoke this api.
Please suggest
You can call consumer.wakeup() function
consumer.wakeup() is the only consumer method that is safe to call from a different thread. Calling wakeup will cause poll() to exit with WakeupException, or if consumer.wakeup() was called while the thread was not waiting on poll, the exception will be thrown on the next iteration when poll() is called. The WakeupException doesn’t need to be handled, but before exiting the thread, you must call consumer.close(). Closing the consumer will commit off‐ sets if needed and will send the group coordinator a message that the consumer is leaving the group. The consumer coordinator will trigger rebalancing immediately
Runtime.getRuntime().addShutdownHook(new Thread() {
public void run() {
System.out.println("Starting exit...");
consumer.wakeup(); **//1**
try {
mainThread.join();
} catch (InterruptedException e) {
e.printStackTrace();
}
} });
...
Duration timeout = Duration.ofMillis(100);
try {
// looping until ctrl-c, the shutdown hook will cleanup on exit
while (true) {
ConsumerRecords<String, String> records =
movingAvg.consumer.poll(timeout);
System.out.println(System.currentTimeMillis() +
"-- waiting for data...");
for (ConsumerRecord<String, String> record : records) {
System.out.printf("offset = %d, key = %s, value = %s\n",
record.offset(), record.key(), record.value());
}
for (TopicPartition tp: consumer.assignment())
System.out.println("Committing offset at position:" +
consumer.position(tp));
movingAvg.consumer.commitSync();
}
} catch (WakeupException e) {
// ignore for shutdown. **//2**
} finally {
consumer.close(); **//3**
System.out.println("Closed consumer and we are done");
}
ShutdownHook runs in a separate thread, so the only safe action we can take is to call wakeup to break out of the poll loop.
Another thread calling wakeup will cause poll to throw a WakeupException. You’ll want to catch the exception to make sure your application doesn’t exit unexpect‐ edly, but there is no need to do anything with it.
Before exiting the consumer, make sure you close it cleanly.
full example at:
https://github.com/gwenshap/kafka-examples/blob/master/SimpleMovingAvg/src/main/java/com/shapira/examples/newconsumer/simplemovingavg/SimpleMovingAvgNewConsumer.java
In an IOCP Winsock2 client, after ConnectEx() times-out on an unsuccessful connection attempt, the following happens:
An "IO completion" is queued to the associated IO Completion Port.
GetQueuedCompletionStatus() returns FALSE.
WSAGetOverlappedResult() returns WSAETIMEDOUT.
What determines the timeout period between calling ConnectEx() and 1 above? How can I shorten this timeout period?
I know that it is possible to wait for ConnectEx() by passing it a filled-out structure OVERLAPPED.hEvent = WSACreateEvent() and then waiting for this event, e.g. with WaitForSingleObject(Overlapped.hEvent, millisec) to timeout after no connection has been made for the millisec time period. BUT, that solution is outside the scope of this question because it does not refer to the IOCP notification model.
unfortunatelly look like no built-in option for set socket connect timeout. how minimum i not view this and based on this question - How to configure socket connect timeout - nobody not view too.
one possible solution pass event handle to I/O request and if we got ERROR_IO_PENDING - call RegisterWaitForSingleObject for this event. if this call will be successful - our WaitOrTimerCallback callback function will be called - or because I/O will be complete (with any final status) and at this moment event (which we pass both to I/O request and RegisterWaitForSingleObject) will be set or because timeout (dwMilliseconds) expired - in this case we need call CancelIoEx function.
so let say we have class IO_IRP : public OVERLAPPED which have reference counting (we need save pointer to OVERLAPPED used in I/O request for pass it to CancelIoEx. and need be sure that this OVERLAPPED still not used in another new I/O - so yet not free). in this case possible implementation:
class WaitTimeout
{
IO_IRP* _Irp;
HANDLE _hEvent, _WaitHandle, _hObject;
static VOID CALLBACK WaitOrTimerCallback(
__in WaitTimeout* lpParameter,
__in BOOLEAN TimerOrWaitFired
)
{
UnregisterWaitEx(lpParameter->_WaitHandle, NULL);
if (TimerOrWaitFired)
{
// the lpOverlapped unique here (because we hold reference on it) - not used in any another I/O
CancelIoEx(lpParameter->_hObject, lpParameter->_Irp);
}
delete lpParameter;
}
~WaitTimeout()
{
if (_hEvent) CloseHandle(_hEvent);
_Irp->Release();
}
WaitTimeout(IO_IRP* Irp, HANDLE hObject) : _hEvent(0), _Irp(Irp), _hObject(hObject)
{
Irp->AddRef();
}
BOOL Create(PHANDLE phEvent)
{
if (HANDLE hEvent = CreateEvent(NULL, FALSE, FALSE, NULL))
{
*phEvent = hEvent;
_hEvent = hEvent;
return TRUE;
}
return FALSE;
}
public:
static WaitTimeout* Create(PHANDLE phEvent, IO_IRP* Irp, HANDLE hObject)
{
if (WaitTimeout* p = new WaitTimeout(Irp, hObject))
{
if (p->Create(phEvent))
{
return p;
}
delete p;
}
return NULL;
}
void Destroy()
{
delete this;
}
// can not access object after this call
void SetTimeout(ULONG dwMilliseconds)
{
if (RegisterWaitForSingleObject(&_WaitHandle, _hEvent,
(WAITORTIMERCALLBACK)WaitOrTimerCallback, this,
dwMilliseconds, WT_EXECUTEONLYONCE|WT_EXECUTEINWAITTHREAD))
{
// WaitOrTimerCallback will be called
// delete self here
return ;
}
// fail register wait
// just cancel i/o and delete self
CancelIoEx(_hObject, _Irp);
delete this;
}
};
and use something like
if (IO_IRP* Irp = new IO_IRP(...))
{
WaitTimeout* p = 0;
if (dwMilliseconds)
{
if (!(p = WaitTimeout::Create(&Irp->hEvent, Irp, (HANDLE)socket)))
{
err = ERROR_NO_SYSTEM_RESOURCES;
}
}
if (err == NOERROR)
{
DWORD dwBytes;
err = ConnectEx(socket, RemoteAddress, RemoteAddressLength,
lpSendBuffer, dwSendDataLength, &dwBytes, Irp)) ?
NOERROR : WSAGetLastError();
}
if (p)
{
if (err == ERROR_IO_PENDING)
{
p->SetTimeout(dwMilliseconds);
}
else
{
p->Destroy();
}
}
Irp->CheckErrorCode(err);
}
another possible solution set timer via CreateTimerQueueTimer and if timer expired - call CancellIoEx or close I/O handle from here. difference with event solution - if I/O will be completed before timer expired - the WaitOrTimerCallback callback function will be not automatically called. in case event - I/O subsystem set event when I/O complete (after intial pending status) and thanks to that (event in signal state) callback will be called. but in case timer - no way pass it to io request as parameter (I/O accept only event handle). as result we need save pointer to timer object by self and manually free it when I/O complete. so here will be 2 pointer to timer object - one from pool (saved by CreateTimerQueueTimer) and one from our object (socket) class (we need it for dereference object when I/O complete). this require reference counting on object which incapsulate timer too. from another side we can use timer not for single I/O operation but for several I/O (because it not direct bind to some I/O)
in the ServiceStart() call of a windows service, I create a thread and start it.
Thread1 = New TThread1(false)
In the Execute procedure of the subthread, there is a loop that runs forever and does that the service is supposed to do.
The problem is that when I get an error in this thread, I want to terminate the thread, and stop the service too.
How can I get the service to stop itself if a thread that it has started stops (fails).
A possibility is to use watchdog timers:
in your thread you reset the timer (eg. every time you enter the loop).
when interval of timer is expired, you know that the thread is probably not working anymore, so you can restart the service or what ever...
A better approach might be to catch exceptions in the thread and log them. Or you could catch the exception, log it, then stop the service. That way you are in control of the service stopping and you also have some insight into the errors being generated.
make a call to stop service :
bool StopService(string svr_name)
{
bool ret = false;
if (svr_name.Length > 0)
{
try
{
ServiceController sc = new ServiceController(svr_name);
if (sc.Status == ServiceControllerStatus.Stopped)
{
return true;
}
sc.Stop();
}
catch (Exception)
{
return false;
}
}
return ret;
}