design a threadpool in pure C

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actually this post should be named as “pure C multithreads”, while it’s better to write some real code. a simple threadpool in pure C

exposed APIs

at most simple case, what a threadpool object should do? 

thpool_init(num_threads);
thpool_destory(threapool_obj);
thpool_add_work(callback, args); 
// so user define event callback() can be passed in;

threadpool is used to assign jobs (from job list) to a thread. so joblist should be an internal class; and it’s better to package thread, job as separate class too; to add work, what kind of funcs need for joblist ? at least, to add new job(from outside) to the joblist.

internal structures:

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struct thread {
 	int id;
 	pthread_t thread;   //pthread_t is a unsigned long int; it's system assigned
 	threadpool *thpool;  //so thread know its domain
}
struct job {
	(void*) func(void*); // each job/task should have a callback func
	(void*) func_arg ; //and func args
	//since consider joblist as a list, it's helpful to add pointers to neighbors
	job* prev;
	job* next;
}
struct jobqueue {
    int num_jobs;
    job* front;
    job* rear;
    //some flags to support add new node(job) to the list
}    
   	 
struct threadpool_ {
    thread* threads_array;
    jobqueue job_queue;
    // some flags
 }

consider syncronlization

will multi threads call add_task() simutaneously? if so, jobqueue should have a mutex object;

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  struct jobqueue {
    int num_jobs;
    job* front;
    job* rear;
    pthread_mutex_t  jq_mutex;
}

during threadpool initialization, will all threads be created simultaneously and immediately? if not, there should be thread status flags (creating, exisiting-but-idle, working, died); and to update these flags need protect by mutex object; 

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struct threadpool_ {
    thread* threads_array;
    jobqueue job_queue;
    int num_threads; //stands for the number of all existing threads
    pthread_mutex_t tp_mutex;
 }

this is an interesting, when design a lib, what’s in my mind. hopefully implement by the end of week.