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pthread works fine only if the number of threads is small


By : Ben Brookshire
Date : September 17 2020, 03:00 AM
I wish this helpful for you 50000 threads is insane. You are most likely running out of memory to allocate stacks for the threads. In general, to get the most out of your CPU through parallelism you only need as many threads as there are CPU cores - that is the limit on the amount of actual concurrency you can get in the hardware. Any more threads, and you are just using up resources for the overhead of thread creation and context switches.
Instead, create a pool of threads equal to the number of cores you have, and break your image up into chunks, and schedule those onto the threads you created.
code :


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pthread accessing it from a Class, variables are lost, when directly works fine


By : wolff
Date : March 29 2020, 07:55 AM
wish of those help c is destroyed when StartThread() returns, meaning hello_helper() is using a dangling pointer resulting in undefined behaviour.
Change to:
code :
void StartThread(){
    C* c = new C();
    c->pickup = 6;

    pthread_t t;
    pthread_create(&t, NULL, &C::hello_helper, c);
}
static void *hello_helper(void *context)
{
    C* c = static_cast<C*>(context);
    c->hello();
    delete c;
    return 0;
} 

re-using threads with the same number pthread


By : Explorer Global
Date : March 29 2020, 07:55 AM
will help you In this code, the "thread number" is entirely your own construct, so you can decide on the rules for how it should be used.

Getting .dex 64K error on a small app that works fine on a different PC


By : John
Date : March 29 2020, 07:55 AM
Any of those help
The only dependency as such is the 'bluealliance spectrum color picker',

Pthread Best way to wake a number of threads


By : kfquinn
Date : March 29 2020, 07:55 AM
fixed the issue. Will look into that further You can indeed use a condition variable for this. The way it works is that your condition is over some shared variable that the main thread sets to indicate that the worker threads should continue. You do require a mutex because you do have a shared resource - the shared variable that the main thread sets and the worker threads read.
Something like:
code :
/* shared variables */
int run_iteration = -1;
pthread_mutex_t iteration_lock = PTHREAD_MUTEX_INITIALIZER;
pthread_cond_t iteration_cond = PTHREAD_COND_INITIALIZER;
int current_iteration = 0;

while (... )
{
    /* Wait for main to signal start of current_iteration */
    pthread_mutex_lock(&iteration_lock);
    while (run_iteration < current_iteration)
        pthread_cond_wait(&iteration_cond, &iteration_lock);
    pthread_mutex_unlock(&iteration_lock);

    /* ... Execute current_iteration ... */

    current_iteration++;
}
/* signal start of next iteration */
pthread_mutex_lock(&iteration_lock);
run_iteration++;
pthread_cond_broadcast(&iteration_cond);
pthread_mutex_unlock(&iteration_lock);

Keeping number of threads constant with pthread in C


By : texruska
Date : March 29 2020, 07:55 AM
Hope this helps Your problem is that worker is not incremented until the new thread actually starts and gets to run - in the meantime, the main thread loops around, checks workers, finds that it hasn't changed, and starts another thread. It can repeat this many times, creating far too many threads.
So, you need to increment worker in the main thread, when you've decided to create a new thread.
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