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As Stuart already stated - windows is not a real-time operating system.
You might find this article[^] on the subject interesting.
However, I'm curious about why you need to send data with such accuracy you seem to be aiming for. Since you're using UDP sockets there's always going to be some kind of network latency that you cannot do anything about and it may not be the same for each packet sent.
It seems to me as if this is about RTP, i.e. Real-time Transport Protocol, since the name of your class is RTPEngine.
If this is the case then you shouldn't have to worry about timing when sending the data. Every RTP-packet has a timestamp that the receiver should use in order to figure out when the media data in the packet should be played.
Read more about RTP here[^].
If you cannot make use of the timestamp in the RTP-packets, or if this is really not about RTP, I'd try the following:- Create a sending worker thread that reads data packets from a queue, e.g.
std::queue; the packets are added to the queue by another thread, probably the main thread. - The sending thread waits on a semaphore, with e.g.
::WaitForMultipleObjects(), that is released once for each packet added to the queue. The trick here is that a thread waiting on a synchronization object, such as a semaphore, gets a temporary priority boost when the object is signalled which means that it will be scheduled to run ASAP. - Each data packet has a waitable timer created and set by the thread that adds the packets to the queue. The sending thread then waits on the timer and sends the data when that the timer is signalled.
I would create a class that represents a packet with a waitable timer as a member. I would also use reference counting smart pointers that reflects the data packets as elements of the queue; this way I don't have to worry about writing cleaning up code in my sending thread. When the object goes out of scope everything is released - heap and waitable timers.
For more information on worker threads - read this[^].
For more information on reference counting smart pointer - read this[^] and some examples here[^].
"It's supposed to be hard, otherwise anybody could do it!" - selfquote
"High speed never compensates for wrong direction!" - unknown
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The reason is not so much the exact timing but the available memory on the other side.
The receiving end is not another computer but a phone. Its an audio stream from a tts-server.
And the phone has only limited capacity so we cannot simply flood it since the sending end works much much faster than the processing of the stream at the receiving end. Therefor we wanted to build in something like a brake. That´s what the variable RTPOverlap is for. At the moment at a value of 10% (0.1). So the sending time of each RTP packet only overlaps with the previous one by about 10%. And these 10 percent are calculated from the playback time that one packet actually needs. Which is about 10ms for an RTP packet of 480 bytes. Meaning we send one packet and then the next comes after 9ms and so on.
Only ... it doesn´t work.
And of course I already have a 'sending worker'. The synthesizer of the tts-server works very fast. So I store the synthesized packages in one class like a scheduler and send them piece by piece away.
By the way, I am familiar with (no specialist, but I´ll find my way around) worker threads and smart pointers and RTP. I´ll look into your links now, anyway .. thanks so far.
Souldrift
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It could be the use of the clock() function; on your XP machine it seems to have a much coarser granularity as the time isn't changing at all in the loop. I always use GetTickCount() for millisecond timing - you can work with integers and don't have to bother doing any division. It's never going to be accurate to a millisecond though; I tried a similar loop on my system and only got a different value about every 15 ms even though I was continually calling the function.
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I don´t think so anymore. I now work with FILETIME (see code from Stuart Dootson). And I still got the same trouble.
Souldrift
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I just found something else. A little disturbing. On our server machine (WIN XP) the Timer ALWAYS sleeps for 15.625ms. If it goes to sleep at all, that is. So this seems to be some kind of minimum time-slice (or a multiplied version of it).
On my own developing computer (Vista) I don´t have theis kind of time-slices. The Timer sleeps for 9ms, then for 10ms and thereafter for 8ms.
Does anybody now if one can manually control these time-slices?
Souldrift
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There's some references on the web to the minimum timer period being 10 ms for uniprocessor systems and 15 ms for multiprocessor. It could also be different depending on whether it's 32 or 64 bit Windows.
The minimum on my system seems to be 15 ms - that's on Vista 32-bit with a dual-core processor.
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Yeah, this would make our efforts kind of hopeless.
But I just found out another little something. It doesn´t seem to be a Vista-XP-thing. But a network-thing. Whatever computer I use as a server, as long as the client comes in via network, the timer sleeps like 15.something millis. If server and client are on the same machine, there doesn´t seem to be a minimum time-slice (or it´s below what I saw so far). The timer sleeps as long (or brief) as I want.
Souldrift
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By the way. I want to thank all who tried and helped me (not only in this thread) so far. This forum has brought me forward quite a bit.
I love the hivemind  .
Cheers
Souldrift
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I just tried to not let the thread sleep or create a wait object or anything.
I simply went into a while-loop. Endlessly. Where I fetched and printed the system time.
This was the result
RTPEngine: Time now = 128911153781458000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781458000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781458000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781458000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781458000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781458000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781458000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781458000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781458000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781458000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781458000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781458000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781458000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781458000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781458000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781458000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781458000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781614000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781614000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781614000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781614000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781614000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781614000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781614000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781614000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781614000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781614000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781614000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781614000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781614000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781614000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781614000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781614000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781614000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781614000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781614000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781614000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781614000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781614000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781614000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781614000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781614000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781614000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781770000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781770000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781770000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781770000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781770000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781770000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781770000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781770000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781770000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781770000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781770000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781770000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781770000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781770000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781770000.000000, send time = 12891115378155.598000.
RTPEngine: Time now = 128911153781770000.000000, send time = 12891115378155.598000.
And so on ... it always jumps 15,6ms forward. After it counted and counted it just jumps. Ar the time windows for a thread THAT small? Like smaller than 100ms?
The code was this one:
GetSystemTimeAsFileTime((FILETIME*)&ftNow);
now = double(ftNow.QuadPart);
m_pLogger->Out( Logger::DEBUG, "RTPEngine: Time now = %f.\n", now );
int tmp = 0;
while( 1 )
{
if( tmp >= 20 )
{
m_pLogger->Out( Logger::DEBUG, "RTPEngine: Time now = %f, send time = %f.\n", now, m_dPacketSendTime );
tmp = 0;
}
tmp++;
GetSystemTimeAsFileTime((FILETIME*)&ftNow);
now = double(ftNow.QuadPart);
}
With thethoughts I wish you all a nice weekend ...
Souldrift
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Souldrift wrote: And so on ... it always jumps 15,6ms forward
Here's what Mark Russinovitch and David Solomon say in Windows Internals
On Windows 2000 Professional and Windows XP, threads run by default for 2 clock intervals; on Windows Server systems, by default, a thread runs for 12 clock intervals. The rationale for the longer default value on server systems is to minimize context switching. By having a longer quantum, server applications that wake up as the result of a client request have a better chance of completing the request and going back into a wait state before their quantum ends
The length of the clock interval varies according to the hardware platform. The frequency of the clock interrupts is up to the HAL, not the kernel. For example, the clock interval for most x86 uniprocessors is about 10 milliseconds and for most x86 multiprocessors it is about 15 milliseconds. (The actual clock rate is not exactly a round number of milliseconds—see the following experiment for a way to check the actual clock interval.)
EXPERIMENT: Determining the Clock Interval Frequency
The Windows GetSystemTimeAdjustment function returns the clock interval. To determine the clock interval, download and run the Clockres program[^] from http://www.sysinternals.com.
That kind of confirms what you're seeing (and what I see - which is 15.625, or 500/32).
HOWEVER!!!! I steered you wrong with waitable timers. I mistook them for a TimerQueueTimer in my memory. Try this:
#include <Windows.h>
#include <tchar.h>
#include <iostream>
void ReportTime(const char* message, LONGLONG const& when)
{
std::cout << message << double(when)/10000.0 << std::endl;
}
LONG count;
LARGE_INTEGER liStart, liEnd, liFreq;
VOID CALLBACK DoSendHere(__in_opt LPVOID lpArgToCompletionRoutine,
__in DWORD dwTimerLowValue,
__in DWORD dwTimerHighValue)
{
QueryPerformanceCounter(&liEnd);
count++;
}
void SendLoop()
{
HANDLE hTimerQueue = CreateTimerQueue();
HANDLE hTimer;
count = 0;
CreateTimerQueueTimer(&hTimer, hTimerQueue, (WAITORTIMERCALLBACK)&DoSendHere, 0 , 1, 1, WT_EXECUTEINTIMERTHREAD);
QueryPerformanceCounter(&liStart);
::SleepEx(65, TRUE);
LONG lCount = count;
QueryPerformanceFrequency(&liFreq);
DeleteTimerQueueTimer(hTimerQueue, hTimer, 0);
std::cout << "Time = " << double(liEnd.QuadPart-liStart.QuadPart) / double(liFreq.QuadPart) << std::endl;
std::cout << "count = " << lCount << std::endl;
}
int _tmain(int argc, _TCHAR* argv[])
{
SendLoop();
return 0;
}
QueryPerformanceCounter lets you see much higher resolution time than other Windows timers (processor clock speed, effectively), so it's good for observing small time periods.
The CreateTimerQueueTimer call is creating a timer that has a 1ms period. So to demonstrate the number of timer expirations in a time period, I increment a counter in the timer callback and measure the time spent counting with the performance counter.
And the results? Consistently within ±40µs of countms.
Schweet.
Java, Basic, who cares - it's all a bunch of tree-hugging hippy cr*p
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Bah, you beat me to it... 
"It's supposed to be hard, otherwise anybody could do it!" - selfquote
"High speed never compensates for wrong direction!" - unknown
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Sorrreeeee 
Java, Basic, who cares - it's all a bunch of tree-hugging hippy cr*p
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"It's supposed to be hard, otherwise anybody could do it!" - selfquote
"High speed never compensates for wrong direction!" - unknown
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Uhh, thanks, I´ll try that out in a moment.
Thanks for the writings on Windows Internals. Who could have known such a thing . Very interesting.
Two things, though. Why do you set a sleep time of 65ms (instead of infinite)? And I don´t see why this should circumvent the 15ms time-slice. QueryPerformanceCounter might 'see' higher resolution, but if the thread sleeps for 15ms, there´s nothing to see? Or is there?
Souldrift
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The 65ms is just an example time - it can't be infinite because I want it to terminate The thing that's seeing past the 15.625 timer resolution is the TimerQueueTimer. That has a resolution of 1ms.
The program is intended to show that the timer callback is called with a resolution of 1ms, so could be used in your case, so long as your thread can remain the active thread.
Java, Basic, who cares - it's all a bunch of tree-hugging hippy cr*p
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Okay, I thought so (after some thinking). Now if you will bear with me one more time, I´m not quite sure how to understand (handle) this regarding my case.
For example if I use this (cause 9ms are appx. the time I need to wait before sending)
CreateTimerQueueTimer(&hTimer, hTimerQueue, (WAITORTIMERCALLBACK)&DoSendHere, 0 , 9, 1, WT_EXECUTEINTIMERTHREAD);
QueryPerformanceCounter(&liStart);
::SleepEx(65, TRUE);
The callback func should with a 65ms sleep be called like 7 times. Though my log shows 54.
I guess, this is because the timer doesn´t stop after my sleep or my sending. So the next question would be, how do I stop it? I know, i doesn´t even have to be periodic for what I need (so it would stop by itself), but I´m trying to understand the structure. I added a DeleteTimerQueueEx( hTimerQueue, NULL ); but it crashes now at that point.
Souldrift
Edit: And why does it not call the callback func when I take away the sleepEx()?? Is it dependant on the thread being asleep?
If I do this
CreateTimerQueueTimer(&hTimer, hTimerQueue, (WAITORTIMERCALLBACK)&DoSendHere, 0 , 1, 0, WT_EXECUTEINTIMERTHREAD);
QueryPerformanceCounter(&liStart);
::SleepEx(10, TRUE);
it doesn´t enter, either.
modified on Monday, July 6, 2009 4:32 AM
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Souldrift wrote: CreateTimerQueueTimer(&hTimer, hTimerQueue, (WAITORTIMERCALLBACK)&DoSendHere, 0 , 9, 1, WT_EXECUTEINTIMERTHREAD);
You're asking for a timer with an initial delay of 9ms and periodic delays after that of 1ms.
Souldrift wrote: DeleteTimerQueueEx( hTimerQueue, NULL );
Think that should be DeleteTimerQueueTimer( hTimerQueue, hTimer, 0 );. That worked for me, anyway.
Souldrift wrote: And why does it not call the callback func when I take away the sleepEx()?? Is it dependant on the thread being asleep?
The thread needs to be in an alertable state - look at the MSDN documentation[^] for what that means.
Java, Basic, who cares - it's all a bunch of tree-hugging hippy cr*p
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Souldrift wrote: it always jumps 15,6ms forward
I doubt the granularity and accuracy of the time value returned by ::GetSystemTimeAsFileTime(). Even though the FILETIME structure is a time value where the least significant bit represents 100 nanoseconds, it doesn't mean that it has an accuracy of 100 nanosecs.
It's like looking at your watch, measuring a time with the needle showing seconds and then multiplying the value by 1,000,000 and claim you measured with microsecond accuracy.
For time measurements of this kind you should you the performance timer; ::QueryPerformanceCounter() and ::QueryPerformanceFrequency().
It will give you the best accuracy available on your hardware.
Read here[^] for more info on the high resolution performance counter.
"It's supposed to be hard, otherwise anybody could do it!" - selfquote
"High speed never compensates for wrong direction!" - unknown
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How can I make a trunc() function in C++,
Example:
trunc(7.1) = 7;
trunc(7.6) = 8;
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What function? Just cast it to an integer. Or if you want a function:
__inline int trunc(float f)
{
return (int)f;
}
It is a crappy thing, but it's life -^ Carlo Pallini
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If I do it in this way, the results are:
trunc(7.1) = 7;
trunc(7.6) = 7;
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Oh sorry, I overlooked your previous post. You can use one of those flooring or ceiling functions.
[Added] OK, Stuart just replied with a floor function at the same time. [/added]
It is a crappy thing, but it's life -^ Carlo Pallini
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Presuming you want similar behaviour for numbers < 0
trunc(-7.1) = -7;
trunc(-7.6) = -8;
then this should work
int trunc(double d) { return floor(d+0.5); }
Java, Basic, who cares - it's all a bunch of tree-hugging hippy cr*p
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rounded_num = (int)(num + (num < 0 ? -0.5 : 0.5));
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You call it trunc(), but that is the expected behaviour of round() function.
If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler.
-- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong.
-- Iain Clarke
[My articles]
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