I am trying to write a simple D program with two threads (main and one spawned in main) with a daughter thread receiving message from the parent thread. Here is my piece:
import std.stdio;
import core.thread;
import std.concurrency;
import std.c.stdio;
extern (C) int kbhit();
void readSignal(){
for(;;){
bool stop = receiveOnly!bool();
if(!stop)
writeln("reading signal...");
else
writeln("stop reading signal...");
Thread.getThis.sleep(1.seconds);
}
}
int main()
{
auto reader = spawn(&readSignal);
bool stop = false;
while(true){
if(kbhit()){
stop = true;
}
option 1: reader.send(stop);
option 2: send(reader, stop);
}
}
return 0;
}
Basically I wait for a keyboard hit and the intend to pause the spawned thread.
Neither of options (option 1 by Andrei Alexandrescu and option 2 as in dlang docs) work for me. What do i do wrong?
It looks to me that your main thread is spinning very hard, sending thousands and thousands of messages to the reader. The reader, however, is only reading one per second. The 'true' message is backed up behind a massive number of 'false' messages.
For a situation like this, you may be better off using a shared variable, rather than using messages. Both threads will be able to safely read and write from it.
as mentioned you are flooding the client thread.
Try adding a sleep like this
Thread.sleep(dur!"msecs"(1500));
As mentioned by duselbaer and Anders S, in your example, the number of sends is huge, but the number of receives is limited by the sleep. So, when the thread should actually get a true, it is already preceded by an overwhelming number of falses in the queue.
Generally, if the child thread is able to receive faster than the parent thread sends, it's fine. Here is a working example produced from your code. The sleep calls may be substituted by doing some work, but the relation must generally hold.
import std.stdio;
import core.thread;
import std.concurrency;
import core.stdc.stdio;
extern (C) int kbhit();
void readSignal() {
for(int i = 0; ; i++) {
bool stop = receiveOnly!bool();
if(!stop)
writeln("reading signal... ", i);
else
{
writeln("stop reading signal...");
break;
}
Thread.getThis.sleep(1.msecs); // this should be no more than below
}
}
int main() {
auto reader = spawn(&readSignal);
bool stop = false;
while(!stop) {
if(kbhit()) {
stop = true;
}
send(reader, stop); // option 1
// reader.send(stop); // option 2 does the same thing as above via UFCS
Thread.getThis.sleep(1.msecs); // this should be no less than above
}
return 0;
}
Related
I am trying to synchronize threads writing data to a text file in a class by using Monitor, but in my code it seems that the else statement is never evaluated, is this the correct use of monitor for thread synchronization?
void Bank::updatefile()
{
Thread^ current = Thread::CurrentThread;
bool open = false;
current->Sleep(1000);
while (!open)
{
if (Monitor::TryEnter(current))
{
String^ fileName = "accountdata.txt";
StreamWriter^ sw = gcnew StreamWriter(fileName);
for (int x = 0; x < 19; x++)
sw->WriteLine(accountData[x]);
sw->Close();
Monitor::Pulse;
Monitor::Exit(current);
current->Sleep(500);
open = true;
}
else
{
Monitor::Wait(current);
current->Sleep(500);
}
}
}
You're passing an object to Monitor::TryEnter that is specific to the thread in which it is executing (i.e. Thread^ current = Thread::CurrentThread;). No other threads are using the same object (they're using the one for their own thread). So there's never a collision or locking conflict.
Try creating some generic object that's shared among the threads, something higher up in the Bank class. Then use that for your TryEnter call.
Your use of Monitor is partially correct. The object you're using for locking is not correct.
Monitor
Monitor::Pulse is unnecessary here. Just Exit the monitor, and the next thread will be able to grab the lock.
Monitor::Wait is incorrect here: Wait is supposed to be used when the thread has the object already locked. Here, you have the object not locked yet.
In general, Pulse and Wait are rarely used. For locking for exclusive access to a shared resource, Enter, TryEnter, and Exit are all you need.
Here's how your use of Monitor should be written:
Object^ lockObj = ...;
bool done = false;
while(!done)
{
if(Monitor::TryEnter(lockObj, 500)) // wait 500 millis for the lock.
{
try
{
// do work
done = true;
}
finally
{
Monitor::Exit(lockObj);
}
}
else
{
// Check some other exit condition?
}
}
or if the else is empty, you can simplify it like this:
Object^ lockObj = ...;
Monitor::Enter(lockObj); // Wait forever for the lock.
try
{
// do work
}
finally
{
Monitor::Exit(lockObj);
}
There is a class that Microsoft provides that makes this all easier: msclr::lock. This class, used without the ^, makes use of the destructor to release the lock, without a try-finally block.
#include <msclr\lock.h>
bool done = false;
while(!done)
{
msclr::lock lock(lockObj, lock_later);
if (lock.try_acquire(500)) // wait 500 millis for the lock to be available.
{
// Do work
done = true;
}
} // <-- Monitor::Exit is called by lock class when it goes out of scope.
{
msclr::lock lock(lockObj); // wait forever for the lock to be available.
// Do work
} // <-- Monitor::Exit is called by lock class when it goes out of scope.
The object to lock on
Thread::CurrentThread is going to return a different object on each thread. Therefore, each thread attempts to lock on a different object, and that's why all of them succeed. Instead, have one object, created before you spawn your threads, that is used for locking.
Also, instead of opening & closing the file on each thread, it would be more efficient to open it once, before the threads are spawned, and then just use that one StreamWriter from each of the threads. This also gives you a obvious object to lock on: You can pass the StreamWriter itself to Monitor::Enter or msclr::lock.
Is there a standard function to receive messages concurrent, but non-blocking? It seems like all the functions available in std.concurrency are blocking and the closest I found to something that is non-blocking is receiveTimeout however it still waits until the timeout. I would like it to return immediately if there are no messages passed to the thread.
Here is what I came up with using receiveTimeout.
module main;
import std.concurrency;
import std.stdio : writefln, readln;
import core.time;
import core.thread;
void spawnedFunc() {
while (true) {
receiveTimeout(
dur!("nsecs")(1),
(int i) { writefln("Received %s", i); }
);
Thread.sleep(dur!("msecs")(100));
}
}
void main() {
auto tid = spawn(&spawnedFunc);
while (true) {
readln();
send(tid, 42);
}
}
Update:
Is my best bet a function like this?
void receiveNonBlocking(T...)(T ops) {
receiveTimeout(
dur!("nsecs")(1),
ops
);
}
...
receiveNonBlocking(
(int i) { writefln("Received %s", i); }
);
Looking at implementation of receiveTimeout:
if( period.isNegative || !m_putMsg.wait( period ) )
return false;
So, providing negative timeout, e.g. nsecs(-1), is the best choice here. And it wouldn't really impact performance, since implementation of non blocking function wouldn't be much different from current one with timeout. Just one more if check to execute before exit for function with negative timeout.
I'll preface this by saying that I'm delving into multithreading for the first time. Despite a lot of reading on concurrency and synchronization, I'm not readily seeing a solution for the requirements I've been given.
Using C++11 and Boost, I'm trying to figure out how to send data from a worker thread to a main thread. The worker thread is spawned at the start of the application and continuously monitors a lock free queue. Objects populate this queue at various intervals. This part is working.
Once the data is available, it needs to be processed by the main thread since another signal will be sent to the rest of the application which cannot be on a worker thread. This is what I'm having trouble with.
If I have to block the main thread through a mutex or a condition variable until the worker thread is done, how will that improve responsiveness? I might as well just stay with a single thread so I have access to the data. I must be missing something here.
I have posted a couple questions, thinking that Boost::Asio was the way to go. There is an example of how signals and data can be sent between threads, but as the responses indicate, things get quickly overly-complicated and it's not working perfectly:
How to connect signal to boost::asio::io_service when posting work on different thread?
Boost::Asio with Main/Workers threads - Can I start event loop before posting work?
After speaking with some colleagues, it was suggested that two queues be used -- one input, one output. This would be in shared space and the output queue would be populated by the worker thread. The worker thread is always going but there would need to be a Timer, probably at the application level, that would force the main thread to examine the output queue to see if there were any pending tasks.
Any ideas on where I should direct my attention? Are there any techniques or strategies that might work for what I'm trying to do? I'll be looking at Timers next.
Thanks.
Edit: This is production code for a plugin system that post-processes simulation results. We are using C++11 first wherever possible, followed by Boost. We are using Boost's lockfree::queue. The application is doing what we want on a single thread but now we are trying to optimize where we see that there are performance issues (in this case, a calculation happening through another library). The main thread has a lot of responsibilities, including database access, which is why I want to limit what the worker thread actually does.
Update: I have already been successful in using std::thread to launch a worker thread that examines a Boost lock::free queue and processes tasks placed it in. It's step 5 in #Pressacco's response that I'm having trouble with. Any examples returning a value to the main thread when a worker thread is finished and informing the main thread, rather than simply waiting for the worker to finish?
If your objective is develop the solution from scratch (using native threads, queues, etc.):
create a thread save queue queue (Mutex/CriticalSection around add/remove)
create a counting semaphore that is associated with the queue
have one or more worker threads wait on the counting semaphore (i.e. the thread will block)
the semaphore is more efficient than having the thread constantly poll the queue
as messages/jobs are added to the queue, increment the semaphore
a thread will wake up
the thread should remove one message
if a result needs to be returned...
setup another: Queue+Semaphore+WorkerThreads
ADDITIONAL NOTES
If you decide to implement a thread safe queue from scratch, take a look at:
Synchronization between threads using Critical Section
With that said, I would take another look at BOOST. I haven't used the library, but from what I hear it will most likely contain some relevant data structures (e.g. a thread safe queue).
My favorite quote from the MSDN:
"When you use multithreading of any sort, you potentially expose
yourself to very serious and complex bugs"
SIDEBAR
Since you are looking at concurrent programming for the first time, you may wish to consider:
Is your objective to build production worthy code , or is this simply a learning exercise?
production? consider us existing proven libraries
learning? consider writing the code from scratch
Consider using a thread pool with an asynchronous callback instead of native threads.
more threads != better
Are threads really needed?
Follow the KISS principle.
The feedback above led me in the right direction for what I needed. The solution was definitely simpler than having to use signals/slots or Boost::Asio as I had previously attempted. I have two lock-free queues, one for input (on a worker thread) and one for output (on the main thread, populated by the worker thread). I use a timer to schedule when the output queue is processed. The code is below; perhaps it is of use to somebody:
//Task.h
#include <iostream>
#include <thread>
class Task
{
public:
Task(bool shutdown = false) : _shutdown(shutdown) {};
virtual ~Task() {};
bool IsShutdownRequest() { return _shutdown; }
virtual int Execute() = 0;
private:
bool _shutdown;
};
class ShutdownTask : public Task
{
public:
ShutdownTask() : Task(true) {}
virtual int Execute() { return -1; }
};
class TimeSeriesTask : public Task
{
public:
TimeSeriesTask(int value) : _value(value) {};
virtual int Execute()
{
std::cout << "Calculating on thread " << std::this_thread::get_id() << std::endl;
return _value * 2;
}
private:
int _value;
};
// Main.cpp : Defines the entry point for the console application.
#include "stdafx.h"
#include "afxwin.h"
#include <boost/lockfree/spsc_queue.hpp>
#include "Task.h"
static UINT_PTR ProcessDataCheckTimerID = 0;
static const int ProcessDataCheckPeriodInMilliseconds = 100;
class Manager
{
public:
Manager()
{
//Worker Thread with application lifetime that processes a lock free queue
_workerThread = std::thread(&Manager::ProcessInputData, this);
};
virtual ~Manager()
{
_workerThread.join();
};
void QueueData(int x)
{
if (x > 0)
{
_inputQueue.push(std::make_shared<TimeSeriesTask>(x));
}
else
{
_inputQueue.push(std::make_shared<ShutdownTask>());
}
}
void ProcessOutputData()
{
//process output data on the Main Thread
_outputQueue.consume_one([&](int value)
{
if (value < 0)
{
PostQuitMessage(WM_QUIT);
}
else
{
int result = value - 1;
std::cout << "Final result is " << result << " on thread " << std::this_thread::get_id() << std::endl;
}
});
}
private:
void ProcessInputData()
{
bool shutdown = false;
//Worker Thread processes input data indefinitely
do
{
_inputQueue.consume_one([&](std::shared_ptr<Task> task)
{
std::cout << "Getting element from input queue on thread " << std::this_thread::get_id() << std::endl;
if (task->IsShutdownRequest()) { shutdown = true; }
int result = task->Execute();
_outputQueue.push(result);
});
} while (shutdown == false);
}
std::thread _workerThread;
boost::lockfree::spsc_queue<std::shared_ptr<Task>, boost::lockfree::capacity<1024>> _inputQueue;
boost::lockfree::spsc_queue<int, boost::lockfree::capacity<1024>> _outputQueue;
};
std::shared_ptr<Manager> g_pMgr;
//timer to force Main Thread to process Manager's output queue
void CALLBACK TimerCallback(HWND hWnd, UINT nMsg, UINT nIDEvent, DWORD dwTime)
{
if (nIDEvent == ProcessDataCheckTimerID)
{
KillTimer(NULL, ProcessDataCheckPeriodInMilliseconds);
ProcessDataCheckTimerID = 0;
//call function to process data
g_pMgr->ProcessOutputData();
//reset timer
ProcessDataCheckTimerID = SetTimer(NULL, ProcessDataCheckTimerID, ProcessDataCheckPeriodInMilliseconds, (TIMERPROC)&TimerCallback);
}
}
int main()
{
std::cout << "Main thread is " << std::this_thread::get_id() << std::endl;
g_pMgr = std::make_shared<Manager>();
ProcessDataCheckTimerID = SetTimer(NULL, ProcessDataCheckTimerID, ProcessDataCheckPeriodInMilliseconds, (TIMERPROC)&TimerCallback);
//queue up some dummy data
for (int i = 1; i <= 10; i++)
{
g_pMgr->QueueData(i);
}
//queue a shutdown request
g_pMgr->QueueData(-1);
//fake the application's message loop
MSG msg;
bool shutdown = false;
while (shutdown == false)
{
if (GetMessage(&msg, NULL, 0, 0))
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
else
{
shutdown = true;
}
}
return 0;
}
I have a thread class with two functions:
using namespace System::Threading;
public ref class SecThr
{
public:
int j;
void wralot()
{
for (int i=0; i<=400000;i++)
{
j=i;
if ((i%10000)==0)
Console::WriteLine(j);
}
}
void setalot()
{
Monitor::Enter(this);
for (int i=0; i<=400000;i++)
{
j=7;
}
Monitor::Exit(this);
}
};
int main(array<System::String ^> ^args)
{
Console::WriteLine("Hello!");
SecThr^ thrcl=gcnew SecThr;
Thread^ o1=gcnew Thread(gcnew ThreadStart(thrcl, &SecThr::wralot));
Thread^ o2=gcnew Thread(gcnew ThreadStart(thrcl, &SecThr::setalot));
o2->Start();
o1->Start();
o1->Join();
o2->Join();
So, for locking "setalot" function i've used MOnitor::Enter-Exit block. But the output is like i'm running only one thread with function "wralot"
0
10000
20000
30000
40000
7 //here's "setalot" func
60000
e t.c.
Why all the output data is not changed to const (7) by "setalot" func
I think you've misunderstood what Monitor::Enter does. It's only a cooperative lock - and as wralot doesn't try to obtain the lock at all, the actions of setalot don't affect it. It's not really clear why you expected to get a constant output of 7 due to setalot - if wralot did try to obtain the lock, it would just mean that one of them would "win" and the other would have to wait. If wralot had to wait, there'd be no output while setalot was running, and then wralot would go do its thing - including setting j to i on every iteration.
So basically, both threads are starting, and setalot very quickly sets j to 7 a lot of times... that's likely to complete in the twinkling of an eye in computer terms, compared with a Console.WriteLine call. I suggest you add a call to Console::WriteLine at the end of setalot so you can see when it's finished. Obviously after that, it's completely irrelevant - which is why you're seeing 60000, 70000 etc.
I'm working on a Qt application to control an industrial camera, and in particular I need to trigger the camera at a particular time (when various illumination settings have been put in place, for example), and wait until a frame is returned. In the simplest case, the following code does the job nicely:
void AcquireFrame()
{
// Runs in the main GUI thread:
camera -> m_mutex.lock();
camera -> frameHasArrived = false;
camera -> m_mutex.unlock();
camera -> triggerImageAcquisition();
forever
{
camera -> m_mutex.lock()
bool isReady = camera -> frameHasArrived;
camera -> m_mutex.unlock()
if (isReady)
{
return;
}
else
{
Sleep(10);
}
}
}
void callback(camera *)
{
// Called by the camera driver from a separate OS thread - not a Qt thread -
// when a frame is ready:
camera -> m_mutex.lock();
camera -> frameHasArrived = true;
camera -> m_mutex.unlock();
}
...and most of the time this works perfectly well. However, this being the real world, occasionally the camera will fail to receive the trigger or the computer will fail to receive the frame cleanly, and the above code will then go into an infinite loop.
The obvious thing to do is to put in a timeout, so if the frame is not received within a certain time then the image acquisition can be attempted again. The revised code looks like:
void AcquireFrame()
{
camera -> m_mutex.lock();
camera -> frameHasArrived = false;
camera -> m_mutex.unlock();
camera -> triggerImageAcquisition();
QTime timeout;
timeout.start();
forever
{
timeout.restart();
fetch: camera -> m_mutex.lock()
bool isReady = camera -> frameHasArrived;
camera -> m_mutex.unlock()
if (isReady)
{
return;
}
else if (timeout.elapsed() > CAM_TIMEOUT)
{
// Assume the first trigger failed, so try again:
camera -> triggerImageAcquisition();
continue;
}
else
{
Sleep(10);
goto fetch;
}
}
}
Now, the problem is that with this latter version the failure rate (the proportion of 'unsuccessful triggers') is much, much higher - at least an order of magnitude. Moreover, this code too will eventually find itself in an infinite loop where, however many times it tries to re-trigger the camera, it never sees a frame come back. Under these latter circumstances, killing the application and checking the camera reveals that the camera is in perfect working order and patiently waiting for its next trigger, so it doesn't appear to be a camera problem. I'm coming to the conclusion that in fact it's some sort of a system resource issue or a thread conflict, so that Qt's event loop is not allowing the camera callback to be called at the proper time.
Is this likely, and is there in fact a better way of doing this?
Update on 6th June:
For what it's worth, I've seen no more problems since I adopted the method below (having given the camera object an extra member, namely a QWaitCondition called 'm_condition'):
void AcquireFrame()
{
bool frameReceived;
forever
{
camera -> triggerImageAcquisition();
camera -> m_mutex.lock();
frameReceived = camera -> m_condition.wait(&camera->m_mutex, CAM_TIMEOUT);
if (frameReceived)
{
// We received a frame from the camera, so can return:
camera -> m_mutex.unlock();
return;
}
// If we got to here, then the wait condition must have timed out. We need to
// unlock the mutex, go back to the beginning of the 'forever' loop and try
// again:
camera -> m_mutex.unlock();
}
}
void callback (camera *)
{
// Called by the camera driver from a separate OS thread -
// not a QThread - when a frame is ready:
camera -> m_condition.wakeOne();
}
This still has the effect of pausing the main thread until we have either received a frame or experienced a timeout, but now we have eliminated the Sleep() and the Qt event loop remains in full control throughout. It's still not clear to me why the old method caused so many problems - I still suspect some sort of system resource limitation - but this new approach seems to be more lightweight and certainly works better.
Running the AcquireFrame that blocks on mutexes in the GUI thread makes not much sense to me unless you wanted to trade off GUI reponsiveness for latency, but I doubt that you care about the latency here as the camera snaps single frames and you insist on processing them in the busy GUI thread in the first place.
Secondly, there is nothing that Qt would do to prevent the callback from getting called from the other thread, other than the other thread having lower priority and being preempted by higher priority threads completely monopolizing the CPU.
I would simply post an event to a QObject in the GUI thread (or any other QThread!) from the callback function. You can post events from any thread, it doesn't matter -- what matters is the receiver. QCoreApplication::postEvent is a static function, after all, and it doesn't check the current thread at all.
In a complex application you probably want to have the logic in a dedicated controller QObject, and not spread across QWidget-derived classes. So you'd simply post the event to the controller instance.
Do note that posting an event to an idle GUI thread will work exactly the same as using a mutex -- Qt's event loop uses a mutex and sleeps on that mutex and on messages from the OS. The beautiful thing is that Qt already does all the waiting for you, but the wait is interruptible. The posted event should have a high priority, so that it'll end up the first one in the queue and preempt all the other events. When you're ready to acquire the frame, but before you trigger it, you can probably call QCoreApplication::flush(). That's about it.
There should be no problem in having a separate image processor QObject living in a dedicated QThread to leverage multicore machines. You can then process the image into a QImage, and forward that one to the GUI thread using another event, or simply via a signal-slot connection. You can probably also notify the GUI thread when you've acquired the frame but are only beginning to process it. That way it'd be more obvious to the user that something is happening. If image processing takes long, you can even send periodic updates that'd be mapped to a progress bar.
The benchmark results (using release builds) are interesting but in line with the fact that Qt's event queues are internally protected by a mutex, and the event loop waits on that mutex. Oh, the results seem to be portable among mac and windows xp platforms.
Using a naked wait condition is not the fastest way, but using a naked posted event is even slower. The fastest way is to use a queued signal-slot connection. In that case, the cost of posting an event to the same thread (that's what the FrameProcessorEvents::tick() does) seems to be negligible.
Mac
warming caches...
benchmarking...
wait condition latency: avg=45us, max=152us, min=8us, n=1001
queued signal connection latency: avg=25us, max=82us, min=10us, n=1000
queued event latency: avg=71us, max=205us, min=14us, n=1000
Windows XP under VMWare Fusion
Note that results over 1ms are likely due to VMWare being not scheduled at the moment.
warming caches...
benchmarking...
wait condition latency: avg=93us, max=783us, min=8us, n=1000
queued signal connection latency: avg=46us, max=1799us, min=0us, n=1000
queued event latency: avg=117us, max=989us, min=18us, n=1001
Below is the benchmarking code.
#include <cstdio>
#include <limits>
#include <QtCore>
QTextStream out(stdout);
class TimedBase : public QObject
{
public:
TimedBase(QObject * parent = 0) : QObject(parent) { reset(); }
friend QTextStream & operator<<(QTextStream & str, const TimedBase & tb) {
return str << "avg=" << tb.avg() << "us, max=" << tb.usMax << "us, min="
<< tb.usMin << "us, n=" << tb.n;
}
void reset() { usMax = 0; n = 0; usMin = std::numeric_limits<quint32>::max(); usSum = 0; }
protected:
quint64 n, usMax, usMin, usSum;
quint64 avg() const { return (n) ? usSum/n : 0; }
void tock() {
const quint64 t = elapsed.nsecsElapsed() / 1000;
usSum += t;
if (t > usMax) usMax = t;
if (t < usMin) usMin = t;
n ++;
}
QElapsedTimer elapsed;
};
class FrameProcessorEvents : public TimedBase
{
Q_OBJECT
public:
FrameProcessorEvents(QObject * parent = 0) : TimedBase(parent) {}
public slots: // can be invoked either from object thread or from the caller thread
void tick() {
elapsed.start();
QCoreApplication::postEvent(this, new QEvent(QEvent::User), 1000);
}
protected:
void customEvent(QEvent * ev) { if (ev->type() == QEvent::User) tock(); }
};
class FrameProcessorWait : public TimedBase
{
Q_OBJECT
public:
FrameProcessorWait(QObject * parent = 0) : TimedBase(parent) {}
void start() {
QTimer::singleShot(0, this, SLOT(spinner()));
}
public: // not a slot since it must be always invoked in the caller thread
void tick() { elapsed.start(); wc.wakeAll(); }
protected:
QMutex mutex;
QWaitCondition wc;
protected slots:
void spinner() {
forever {
QMutexLocker lock(&mutex);
if (wc.wait(&mutex, 1000)) {
tock();
} else {
return;
}
}
}
};
FrameProcessorEvents * fpe;
FrameProcessorWait * fpw;
static const int avgCount = 1000;
static const int period = 5;
class FrameSender : public QObject
{
Q_OBJECT
public:
FrameSender(QObject * parent = 0) : QObject(parent), n(0), N(1) {
QTimer::singleShot(0, this, SLOT(start()));
}
protected slots:
void start() {
out << (N ? "warming caches..." : "benchmarking...") << endl;
// fire off a bunch of wait ticks
n = avgCount;
timer.disconnect();
connect(&timer, SIGNAL(timeout()), SLOT(waitTick()));
fpw->reset();
fpw->start();
timer.start(period);
}
void waitTick() {
fpw->tick();
if (!n--) {
if (!N) { out << "wait condition latency: " << *fpw << endl; }
// fire off a bunch of signal+event ticks
n = avgCount;
fpe->reset();
timer.disconnect();
connect(&timer, SIGNAL(timeout()), fpe, SLOT(tick()));
connect(&timer, SIGNAL(timeout()), SLOT(signalTick()));
}
}
void signalTick() {
if (!n--) {
if (!N) { out << "queued signal connection latency: " << *fpe << endl; }
// fire off a bunch of event-only ticks
n = avgCount;
fpe->reset();
timer.disconnect();
connect(&timer, SIGNAL(timeout()), SLOT(eventTick()));
}
}
void eventTick() {
fpe->tick();
if (!n--) {
if (!N) { out << "queued event latency: " << *fpe << endl; }
if (!N--) {
qApp->exit();
} else {
start();
}
}
}
protected:
QTimer timer;
int n, N;
};
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
QThread eThread;
QThread wThread;
eThread.start(QThread::TimeCriticalPriority);
wThread.start(QThread::TimeCriticalPriority);
fpw = new FrameProcessorWait();
fpe = new FrameProcessorEvents();
fpw->moveToThread(&eThread);
fpe->moveToThread(&wThread);
FrameSender s;
a.exec();
eThread.exit();
wThread.exit();
eThread.wait();
wThread.wait();
return 0;
}
#include "main.moc"
How much work is it to detect the trigger state and fire the camera?
If that's relatively cheap - I would have a separate thread just blocking on a trigger event and firing the camera. Then have the main thread informed by a Qt signal sent from the callback function.