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Can anyone tell me how to create more then one thread at a time
is there any such ?
like:
pthread_create (thread, attr, start_routine, arg)
should give me more than one thread at a time.
Your actual question seems to be more like "How can I make sure my tests exercise a potential race condition by calling the same function at the exact same time?"
The answer is, you sort of can't. Imagine your test runs on a single-processor machine. There's no way for the function to be called twice at the same time (but it could partially execute once then start again in the other thread).
Think about other ways to test for race conditions. At the more formal end of the spectrum, you can use tools like Spin and Promela to verify such things, but it's a lot more involved than spawning two threads in a unit test. For more, see here: http://lwn.net/Articles/243851/
A less formal way is to call your function in some way where it will sleep in its middle when the first thread calls it. Then you're very likely to see execution continue with the second call while the first one is suspended. But be mindful of wasting time on this approach, because it mostly validates that you've written the test correctly, and may not prove anything much about the thread safety of your code in practice.
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I have to generate & publish data (as protocol buffer messages) with a frequency of 1Hz and I have been thinking of alternatives to just sticking it into a While loop with a clock() function. Maybe I am over thinking the issue but any advice on the matter would be much appreciated thanks
There are many ways to call a function on a regular interval. Which one is best depends on the situation and needs of the program. There's no single "best way".
A few possibilities (there are many more):
Sit in a loop and sleep for some duration every time round the loop. Simple, easy to understand. But rarely the best solution, since nothing else can happen while you sleep.
Sit in a loop waiting for some event to occur. Like a timer event. Process each event as it arrives - if not enough time has passed, ignore the event (maybe).
Set up a timer with a callback function that will call the function at regular intervals.
If your intervals are very tiny, then maybe spin / busy-wait in a loop and check elapsed time each time around the loop and do something when enough time has passed (rarely a good idea since it will burn a lot of CPU time doing nothing, but sometimes it's the right option).
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I am creating an interactive sudoku board in c++. Whenever the user changes a value, I would like to check if the board is completed. The board will be completed when all spaces on the board are filled. My two ideas of how to do this are:
Create a private data member that holds the amount of filled spaces. To check if the board is completed I will simply have to check if this value equals boardLength^2
Create a member function that iterates through the board and returns false when a blank space is found and true if it goes through the board without finding any blank spaces
Is this a matter of preference, or is there a more accepted/correct way to do this?
Is this a matter of preference, or is there a more accepted/correct way to do this?
There is an accepted and correct way of optimizing, in general:
Optimize for speed or memory footprint when you actually need to, when you identify an actual problem. Your project's unique requirements will govern what constitutes a "problem".
Otherwise, optimize your code for readability and maintainability.
In your particular case:
Chances are that no matter which algorithm you choose, your check will happen so quickly that you will not be able to measure it, and the user will never notice the difference between the simple solution and the "fast" solution. Any attempts to optimize this (at the cost of complexity or readability or time spent writing code) are poor trade-offs.
Use the simplest possible solution. Once finished, if there is a noticeable delay on user input, and you can confirm that it's caused by an inefficient check for board completion, consider ways to improve your algorithm.
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I have an Win32 app that contains 13 SetTimer() calls... I have a doubt: to optimize application performance, would be better to use CreateThread (with infinite loop and Sleep) instead SetTimer? Which of the two ways to a better way and timing of actions?
Sorry for bad english, thanks in advance!
I wouldn't write a custom timer unless you have a very specific need to do so. I'd guess performance difference would be negligible for most applications. Plus you'll run into other issues I'm sure you're not currently considering, like data synchronization, communicating with your GUI thread for user interactions, etc. It's possible you could even make performance worse.
If you feel you have a specific need, state what that need is and maybe we can guide the answer.
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Let's say I have a vector of exact future times of multiple events. I want those events to launch when their respective times have been reached. How do I do this without constantly using if statements to check that the current time is one of those set times? This constant checking, especially if many other things are running in my program (and some of those times may be a bit away from now) will reduce the performance of my program. I'm using c++11, latest version of GCC.
If you're using C++11, it's probably easiest to create a thread, have it sleep until the next alarm time. The most efficient way to store the times for the alarms is probably a priority queue.
If you don't have C++ 11 available, you might consider Boost Threads instead. The standard's threads are based closely on Boost threads, so using them will be fairly similar.
If you don't want to use that, you'll pretty much need to use operating system facilities to do the job. With almost any reasonably modern OS, you can create a thread and have it sleep until the next alarm time, but you'll probably also have something that supports what you want a little more directly (call a function at a specified time). The details of that will be specific to the OS though.
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In my project I have a lot of MATLAB functions. For each function I call Initialize function, when the application starts. I tried to call this functions using parallel_invoke. I tried it several times and allways it takes more time, that code without this. Can somebody explain this ?
Is there is something specific in MATLAB or Initialize functions ?
The Matlab Runtime only has a single interpreter thread, so calling Matlab functions in parallel does not gain you anything: when the first function A is called, the MCR acquires a lock and only releases it when that function exits. Calling another function B during that period results in trying to acquire the lock, which then obviously just blocks until A finishes. The reason you see it taking up more time is probably due to the overhead of the locking/parallel_invoke.
I'm not sure what you mean with for each function I call Initialize function: unless you are using multiple Matlab dlls (which will afaik be less performant than having a single dll) you only need to call it's Initalize/Terminate once.