Author: Johan Hanssen Seferidis
Created: 2011年08月12日
Update: 09/13/2014
 Transfer to multiple job queue structure.
 by elxy
=================================== Compiling =====================================
The library is not precompiled so you have to compile it with your project. The thread pool
uses POSIX threads so if you compile with gcc you have to use the flag -pthread like this:
 gcc main.c thpool.c -pthread -o test
Then run the executable like this:
 ./test
====================================== Usage ======================================
1. Make a thread pool: thpool_t* thpool;
2. Initialise the thread pool with number
 of threads(workers) you want: thpool=thpool_init(4);
3. Add work to the pool: thpool_add_work(thpool, tag, (void*)doSth, (void*)arg);
4. Destroy pool: thpool_destroy(thpool);
=============================== Threadpool Interface ===============================
NAME
 thpool_t* thpool_init(int num_of_threads);
SYNOPSIS
 
 #include <thpool.h>
 thpool_t* thpool_init(int num_of_threads);
DESCRIPTION
 Initialises the threadpool. On success a threadpool structure is returned. Otherwise if memory could not be allocated NULL is returned. The argument which is the number of threads in the threadpool should be a thoughfull choice. A common suggestion is to use as many threads as the ones supported by your cpu.
 Example:
 thpool_t* myThreadpool; //First we declare a threadpool
 myThreadpool=thpool_init(4); //then we initialise it to 4 threads
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NAME
 thpool_add_work(thpool_t* thpool, int tag, void *(*function_p)(void*), void* arg_p);
SYNOPSIS
 
 #include <thpool.h>
 int thpool_add_work(thpool_t* thpool, int tag, void *(*function_p)(void*), void* arg_p);
DESCRIPTION
 Adds work to the job queues. Which queue it will be added to depends on tag (or use hash func). Work is concidered an individual function with an argument. First argument is a pointer to the pool itself. The second argument is a pointer to a function and third argument is a pointer to an argument. To pass multiple arguments just use a struct. If the function you want to pass doesn't fit the parameters of this prototype, use casting. If your function or argument doesn't fit the parameters' and return's value type then you should use casting to avoid warnings from the compiler.
 Example:
 void printSth(char* str); //Prints a text on the screen
 thpool_add_work(thpool, i, (void*)printSth, (void*)str); //Pay attention to the casting
-----------------------------------------------------------------------------------
NAME
 void thpool_destroy(thpool_t* tp_p);
SYNOPSIS
 
 #include <thpool.h>
 void thpool_destroy(thpool_t* tp_p);
DESCRIPTION
 This function will destroy a threadpool. If some threads are working in the pool then thpool_destroy() will wait for them to finish. Once they are finished the threadpool is deallocated releasing all resources back to the system.
 Example:
 thpool_destroy(threadpool_p); //threadpool_p being a pointer to a thpool_t