passing arguments to pthreads
Hi, I have a question about passing multiple arguments to pthreads, the big deal is where the paremeters are kept.. I see two possible solutions.. keep it on static variables that are never deallocated.. or on heap.. so here is my first question
Passing local (stack) variables as arguments to thread is trouble, since the scope of this variables can go away before my thread returns..right? So forget about local variables
So here is the two options I see, static vs heap...
I'm using this model on one of my applications, is the same senario, a function that receives 3 ints as arguments and is called as a thread.. I create a little wrapper... here is the code http://pastebin.com/Air7u0YD
How gurus does this? I free the args on threadfd wrapper since, on my real application can't join the thread, to be honest, is and deatached thread.. Is there something wrong with this strategy, it seems ugly to me....
Cheers,
2014-03-14 16:08 UTC+01:00, Daniel Hilst Selli <[email protected]>:
Quoted 15 lines
Hi, I have a question about passing multiple arguments to pthreads, the big deal is where the paremeters are kept.. I see two possible solutions.. keep it on static variables that are never deallocated.. or on heap.. so here is my first question
Passing local (stack) variables as arguments to thread is trouble, since the scope of this variables can go away before my thread returns..right? So forget about local variables
So here is the two options I see, static vs heap...
I'm using this model on one of my applications, is the same senario, a function that receives 3 ints as arguments and is called as a thread.. I create a little wrapper... here is the code http://pastebin.com/Air7u0YD
Quoted 6 lines
How gurus does this? I free the args on threadfd wrapper since, on my real application can't join the thread, to be honest, is and deatached thread.. Is there something wrong with this strategy, it seems ugly to me....
Cheers,
Hello,
If you don't mind making the start time of the threads a bit slower, you can make every thread copy its data into its local stack. You can either allocate one set of arguments on the stack of the main and then, with a semaphore wait for the thread to copy its data before erasing it with the data for the second thread and so on. Or you can allocate enough memory for the arguments of all the threads, start all the threads, and still with a semaphore wait that all the threads copied their own data to their stack.
You can also make something in-between by allocating enough memory for a fixed number of arguments. But it's becoming complicated to handle for probably no gain.
But actually, I don't really see why you wouldn't join the threads. You must not terminate the function main while the threads are running. If you do, all the threads will be terminated.
Celelibi
Quoted 25 lines · Celelibi
2014-03-14 16:08 UTC+01:00, Daniel Hilst Selli <[email protected]>:
Quoted 15 lines
Hi, I have a question about passing multiple arguments to pthreads, the big deal is where the paremeters are kept.. I see two possible solutions.. keep it on static variables that are never deallocated.. or on heap.. so here is my first question
Passing local (stack) variables as arguments to thread is trouble, since the scope of this variables can go away before my thread returns..right? So forget about local variables
So here is the two options I see, static vs heap...
I'm using this model on one of my applications, is the same senario, a function that receives 3 ints as arguments and is called as a thread.. I create a little wrapper... here is the code http://pastebin.com/Air7u0YDQuoted 6 lines
How gurus does this? I free the args on threadfd wrapper since, on my real application can't join the thread, to be honest, is and deatached thread.. Is there something wrong with this strategy, it seems ugly to me....
Cheers,
Hello,
Quoted 8 lines
If you don't mind making the start time of the threads a bit slower, you can make every thread copy its data into its local stack. You can either allocate one set of arguments on the stack of the main and then, with a semaphore wait for the thread to copy its data before erasing it with the data for the second thread and so on. Or you can allocate enough memory for the arguments of all the threads, start all the threads, and still with a semaphore wait that all the threads copied their own data to their stack.
Making parameters local to threads seems an elegant solution for me, how would I do it? Should I use this? http://pubs.opengroup.org/onlinepubs/007904975/functions/pthread_getspecific.html
Quoted 4 lines
You can also make something in-between by allocating enough memory for a fixed number of arguments. But it's becoming complicated to handle for probably no gain.
This seems what I'm doing right now.. For simple cases seems acceptable but for complex case, it seems to be trouble to handle...
Quoted 4 lines
But actually, I don't really see why you wouldn't join the threads. You must not terminate the function main while the threads are running. If you do, all the threads will be terminated.
I have this cenario, I'm wrinting a layer that will sit between an industrial stack and end user (a programmer)... the stack will call my callback for any events that ocurr, my callback should forward the call to user's callback based on event, in other words, my layer will handle some events, others are passed to user.. The problem is that the stack call my callback from its context and this blocks stack execution until my callback returns, this is the reason I'm creating a new thread in first place.. I can't trust user to return fast, I can't wait for it.. this is why I'm not joining the thread...
Thanks for your help :-)
Cheers...
Quoted 4 lines
Celelibi
2014-03-14 18:30 UTC+01:00, Daniel Hilst Selli <[email protected]>:
Quoted 34 lines · Celelibi
Quoted 25 lines
2014-03-14 16:08 UTC+01:00, Daniel Hilst Selli <[email protected]>:
Quoted 15 lines
Hi, I have a question about passing multiple arguments to pthreads, the big deal is where the paremeters are kept.. I see two possible solutions.. keep it on static variables that are never deallocated.. or on heap.. so here is my first question
Passing local (stack) variables as arguments to thread is trouble, since the scope of this variables can go away before my thread returns..right? So forget about local variables
So here is the two options I see, static vs heap...
I'm using this model on one of my applications, is the same senario, a function that receives 3 ints as arguments and is called as a thread.. I create a little wrapper... here is the code http://pastebin.com/Air7u0YDQuoted 6 lines
How gurus does this? I free the args on threadfd wrapper since, on my real application can't join the thread, to be honest, is and deatached thread.. Is there something wrong with this strategy, it seems ugly to me....
Cheers,
Hello,
Quoted 8 lines
If you don't mind making the start time of the threads a bit slower, you can make every thread copy its data into its local stack. You can either allocate one set of arguments on the stack of the main and then, with a semaphore wait for the thread to copy its data before erasing it with the data for the second thread and so on. Or you can allocate enough memory for the arguments of all the threads, start all the threads, and still with a semaphore wait that all the threads copied their own data to their stack.
Quoted 3 lines
Making parameters local to threads seems an elegant solution for me, how would I do it? Should I use this?
http://pubs.opengroup.org/onlinepubs/007904975/functions/pthread_getspecific.html
I didn't know about pthread_getspecific. But it seems that they only store void*. Not very useful to replace function arguments.
I'd just suggest starting your thread routine with something like:
struct thread_arg *a = arg;
int a1 = a->a1; int a2 = a->a2; int a3 = a->a3;
sem_post(a->sem);
Quoted 13 lines
Quoted 6 lines
You can also make something in-between by allocating enough memory for a fixed number of arguments. But it's becoming complicated to handle for probably no gain.
This seems what I'm doing right now.. For simple cases seems acceptable but for complex case, it seems to be trouble to handle...
Quoted 4 lines
But actually, I don't really see why you wouldn't join the threads. You must not terminate the function main while the threads are running. If you do, all the threads will be terminated.
Quoted 9 lines
I have this cenario, I'm wrinting a layer that will sit between an industrial stack and end user (a programmer)... the stack will call my callback for any events that ocurr, my callback should forward the call to user's callback based on event, in other words, my layer will handle some events, others are passed to user.. The problem is that the stack call my callback from its context and this blocks stack execution until my callback returns, this is the reason I'm creating a new thread in first place.. I can't trust user to return fast, I can't wait for it.. this is why I'm not joining the thread...
Are you sure you need threads? And not just a way to postpone a long function call until you have time to actually call it?
I mean: introducing threads when you don't really need to perform several CPU-intensive actions at the very same time is not always worth it.
Although the idea might seem sexy in the begining, it always lead to synchronization problems. And bugs with threaded programs are just harder to spot and to fix.
Celelibi
Quoted 42 lines · Celelibi
2014-03-14 18:30 UTC+01:00, Daniel Hilst Selli <[email protected]>:
Quoted 34 lines · Celelibi
Quoted 25 lines
2014-03-14 16:08 UTC+01:00, Daniel Hilst Selli <[email protected]>:
Quoted 15 lines
Hi, I have a question about passing multiple arguments to pthreads, the big deal is where the paremeters are kept.. I see two possible solutions.. keep it on static variables that are never deallocated.. or on heap.. so here is my first question
Passing local (stack) variables as arguments to thread is trouble, since the scope of this variables can go away before my thread returns..right? So forget about local variables
So here is the two options I see, static vs heap...
I'm using this model on one of my applications, is the same senario, a function that receives 3 ints as arguments and is called as a thread.. I create a little wrapper... here is the code http://pastebin.com/Air7u0YDQuoted 6 lines
How gurus does this? I free the args on threadfd wrapper since, on my real application can't join the thread, to be honest, is and deatached thread.. Is there something wrong with this strategy, it seems ugly to me....
Cheers,
Hello,
Quoted 8 lines
If you don't mind making the start time of the threads a bit slower, you can make every thread copy its data into its local stack. You can either allocate one set of arguments on the stack of the main and then, with a semaphore wait for the thread to copy its data before erasing it with the data for the second thread and so on. Or you can allocate enough memory for the arguments of all the threads, start all the threads, and still with a semaphore wait that all the threads copied their own data to their stack.
Quoted 3 lines
Making parameters local to threads seems an elegant solution for me, how would I do it? Should I use this?
http://pubs.opengroup.org/onlinepubs/007904975/functions/pthread_getspecific.htmlI didn't know about
pthread_getspecific. But it seems that they only store void*. Not very useful to replace function arguments.
Quoted 6 lines
I'd just suggest starting your thread routine with something like:
structthread_arg*a = arg;int a1 = a->a1; int a2 = a->a2; int a3 = a->a3;
sem_post(a->sem);
I'm not using semaphores here, I just create a wrapper over the real function I want to call with as 3 ints as arguments, something like this
main()
{
int *args = malloc(sizeof(int) * 3);
args[0] = x; args[1] = y; args[2] = z;
pthread_create(th, detached, wrap, args)
}
void *wrap(void *args)
{
real_func(args[0], args[1], args[2]);
free(args);
}
The args are only freed when real_func returns, so I don't see problems and need to use semaphores, did you? Is just this function that I execute as a thread, all others on my layer follow a normal flow, I mean, no parallel stuff...
Quoted 27 lines
Quoted 14 lines
Quoted 7 lines
You can also make something in-between by allocating enough memory for a fixed number of arguments. But it's becoming complicated to handle for probably no gain.
This seems what I'm doing right now.. For simple cases seems acceptable but for complex case, it seems to be trouble to handle...
Quoted 4 lines
But actually, I don't really see why you wouldn't join the threads. You must not terminate the function main while the threads are running. If you do, all the threads will be terminated.
Quoted 9 lines
I have this cenario, I'm wrinting a layer that will sit between an industrial stack and end user (a programmer)... the stack will call my callback for any events that ocurr, my callback should forward the call to user's callback based on event, in other words, my layer will handle some events, others are passed to user.. The problem is that the stack call my callback from its context and this blocks stack execution until my callback returns, this is the reason I'm creating a new thread in first place.. I can't trust user to return fast, I can't wait for it.. this is why I'm not joining the thread...
Are you sure you need threads? And not just a way to postpone a long function call until you have time to actually call it?
Quoted 6 lines
I mean: introducing threads when you don't really need to perform several CPU-intensive actions at the very same time is not always worth it.
Although the idea might seem sexy in the begining, it always lead to synchronization problems. And bugs with threaded programs are just harder to spot and to fix.
I agree, I don't like threads when they aren't needed too, but as a layer I have no control on execution flow, and, the stack is already full of threads..
Still I'm wondering how to postpone this execution, I can execute a signal handler as an alarm or something, but it seems as ugly as threads...
Thanks for your answer :-)
Cheers,
Quoted 4 lines
Celelibi
2014-03-18 23:21 UTC+01:00, Daniel Hilst Selli <[email protected]>:
Quoted 65 lines · Celelibi
Quoted 48 lines
2014-03-14 18:30 UTC+01:00, Daniel Hilst Selli <[email protected]>:
Quoted 40 lines · Celelibi
Quoted 31 lines
2014-03-14 16:08 UTC+01:00, Daniel Hilst Selli <[email protected]>:
Quoted 21 lines
Hi, I have a question about passing multiple arguments to pthreads, the
big deal is where the paremeters are kept.. I see two possible solutions.. keep it on static variables that are never deallocated.. or
on heap.. so here is my first questionPassing local (stack) variables as arguments to thread is trouble, since
the scope of this variables can go away before my thread returns..right?
So forget about local variablesSo here is the two options I see, static vs heap...
I'm using this model on one of my applications, is the same senario, a function that receives 3 ints as arguments and is called as a thread.. I
create a little wrapper... here is the code
http://pastebin.com/Air7u0YDQuoted 6 lines
How gurus does this? I free the args on threadfd wrapper since, on my real application can't join the thread, to be honest, is and deatached thread.. Is there something wrong with this strategy, it seems ugly to me....
Cheers,
Hello,
Quoted 8 lines
If you don't mind making the start time of the threads a bit slower, you can make every thread copy its data into its local stack. You can either allocate one set of arguments on the stack of the main and then, with a semaphore wait for the thread to copy its data before erasing it with the data for the second thread and so on. Or you can allocate enough memory for the arguments of all the threads, start all the threads, and still with a semaphore wait that all the threads copied their own data to their stack.
Quoted 3 lines
Making parameters local to threads seems an elegant solution for me, how would I do it? Should I use this?
http://pubs.opengroup.org/onlinepubs/007904975/functions/pthread_getspecific.htmlI didn't know about
pthread_getspecific. But it seems that they only store void*. Not very useful to replace function arguments.Quoted 6 lines
I'd just suggest starting your thread routine with something like:
structthread_arg*a = arg;int a1 = a->a1; int a2 = a->a2; int a3 = a->a3;
sem_post(a->sem);I'm not using semaphores here, I just create a wrapper over the real function I want to call with as 3 ints as arguments, something like this
main(){ int *args = malloc(sizeof(int) * 3); args[0] = x; args[1] = y; args[2] = z; pthread_create(th, detached, wrap, args) }
Quoted 5 lines
void *wrap(void *args)
{ real_func(args[0], args[1], args[2]); free(args); }
You need to cast args as int*.
Quoted 4 lines
The args are only freed when
real_funcreturns, so I don't see problems and need to use semaphores, did you? Is just this function that I execute as a thread, all others on my layer follow a normal flow, I mean, no parallel stuff...
I thought you wanted to avoid using the heap.
Isn't that code more or less what you had in the pastbin in your first message? Moreover, there are other way of terminating a thread. pthread_cancel for instance.
But... Do your threads terminate? I thought you didn't wanted to join them.
Quoted 9 lines
Quoted 9 lines
Are you sure you need threads? And not just a way to postpone a long function call until you have time to actually call it?
I mean: introducing threads when you don't really need to perform several CPU-intensive actions at the very same time is not always worth it.
Although the idea might seem sexy in the begining, it always lead to synchronization problems. And bugs with threaded programs are just harder to spot and to fix.
Quoted 7 lines
I agree, I don't like threads when they aren't needed too, but as a layer I have no control on execution flow, and, the stack is already full of threads..
Still I'm wondering how to postpone this execution, I can execute a signal handler as an alarm or something, but it seems as ugly as threads...
You're writing a layer between some user code and some backend that generate events (you called "the industrial stack"). Right? What does the main thread executes? Where is the main loop? You may provide a function to the user code that the user code has to call every once is a while. Similar to what GTK does with gtk_main_iteration. This function would process any pending event and call the callback functions. And if the user code do not want to handle the main loop, you can provide a function that loops on that even-processing function. Just like gtk_main.
However, if the main loop of the code is in the backend, then maybe they provide an "idle event". It's a callback that is called when there is no other event.
But if you say the backend is already full of threads... Then adding more may not add much troubles. And if the backend is full of threads, is that really important that you return to the caller ASAP?
Celelibi