/* ********************************
 * 
 * Author:  Johan Hanssen Seferidis
 * Date:    12/08/2011
 * Update:  01/11/2011
 * License: LGPL
 * 
 * 
 *//** @file thpool.h *//*
 ********************************/

/* Library providing a threading pool where you can add work. For an example on 
 * usage you refer to the main file found in the same package */

/* 
 * Fast reminders:
 * 
 * tp           = threadpool 
 * thpool       = threadpool
 * thpool_t     = threadpool type
 * tp_p         = threadpool pointer
 * sem          = semaphore
 * xN           = x can be any string. N stands for amount
 * 
 * */

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <pthread.h>
#include <semaphore.h>
#include <errno.h>

#include "thpool.h"      /* here you can also find the interface to each function */


static int thpool_keepalive=1;

/* Create mutex variable */
pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER; /* used to serialize queue access */




/* Initialise thread pool */
thpool_t* thpool_init(int threadsN){
	thpool_t* tp_p;
	
	if (!threadsN || threadsN<1) threadsN=1;
	
	/* Make new thread pool */
	tp_p=(thpool_t*)malloc(sizeof(thpool_t));                              /* MALLOC thread pool */
	if (tp_p==NULL){
		fprintf(stderr, "thpool_init(): Could not allocate memory for thread pool\n");
		return NULL;
	}
	tp_p->threads=(pthread_t*)malloc(threadsN*sizeof(pthread_t));          /* MALLOC thread IDs */
	if (tp_p->threads==NULL){
		fprintf(stderr, "thpool_init(): Could not allocate memory for thread IDs\n");
		return NULL;
	}
	tp_p->threadsN=threadsN;
	
	/* Initialise the job queue */
	if (thpool_jobqueue_init(tp_p)==-1){
		fprintf(stderr, "thpool_init(): Could not allocate memory for job queue\n");
		return NULL;
	}
	
	/* Initialise semaphore*/
	tp_p->jobqueue->queueSem=(sem_t*)malloc(sizeof(sem_t));                 /* MALLOC job queue semaphore */
	sem_init(tp_p->jobqueue->queueSem, 0, 0); /* no shared, initial value */
	
	/* Make threads in pool */
	int t;
	for (t=0; t<threadsN; t++){
		printf("Created thread %d in pool \n", t);
		pthread_create(&(tp_p->threads[t]), NULL, (void *)thpool_thread_do, (void *)tp_p); /* MALLOCS INSIDE PTHREAD HERE */
	}
	
	return tp_p;
}


/* What each individual thread is doing 
 * */
/* There are two scenarios here. One is everything works as it should and second if
 * the thpool is to be killed. In that manner we try to BYPASS sem_wait and end each thread. */
void thpool_thread_do(thpool_t* tp_p){

	while(thpool_keepalive){
		
		if (sem_wait(tp_p->jobqueue->queueSem)) {/* WAITING until there is work in the queue */
			perror("thpool_thread_do(): Waiting for semaphore");
			exit(1);
		}

		if (thpool_keepalive){
			
			/* Read job from queue and execute it */
			void*(*func_buff)(void* arg);
			void*  arg_buff;
			thpool_job_t* job_p;
	
			pthread_mutex_lock(&mutex);                  /* LOCK */
			
			job_p = thpool_jobqueue_peek(tp_p);
			func_buff=job_p->function;
			arg_buff =job_p->arg;
			thpool_jobqueue_removelast(tp_p);
			
			pthread_mutex_unlock(&mutex);                /* UNLOCK */
			
			func_buff(arg_buff);               			 /* run function */
			free(job_p);                                                       /* DEALLOC job */
		}
		else
		{
			return; /* EXIT thread*/
		}
	}
	return;
}


/* Add work to the thread pool */
int thpool_add_work(thpool_t* tp_p, void *(*function_p)(void*), void* arg_p){
	thpool_job_t* newJob;
	
	newJob=(thpool_job_t*)malloc(sizeof(thpool_job_t));                        /* MALLOC job */
	if (newJob==NULL){
		fprintf(stderr, "thpool_add_work(): Could not allocate memory for new job\n");
		exit(1);
	}
	
	/* add function and argument */
	newJob->function=function_p;
	newJob->arg=arg_p;
	
	/* add job to queue */
	pthread_mutex_lock(&mutex);                  /* LOCK */
	thpool_jobqueue_add(tp_p, newJob);
	pthread_mutex_unlock(&mutex);                /* UNLOCK */
	
	return(1);
}


/* Destroy the threadpool */
void thpool_destroy(thpool_t* tp_p){
	int t;

	while(tp_p->jobqueue->jobsN > 0) {
	 usleep(50000);
	}	
	/* End each thread's infinite loop */
	thpool_keepalive=0; 

	/* Awake idle threads waiting at semaphore */
	for (t=0; t<(tp_p->threadsN); t++){
		if (sem_post(tp_p->jobqueue->queueSem)){
			fprintf(stderr, "thpool_destroy(): Could not bypass sem_wait()\n");
		}
	}

	/* Kill semaphore */
	if (sem_destroy(tp_p->jobqueue->queueSem)!=0){
		fprintf(stderr, "thpool_destroy(): Could not destroy semaphore\n");
	}
	
	/* Wait for threads to finish */
	for (t=0; t<(tp_p->threadsN); t++){
		pthread_join(tp_p->threads[t], NULL);
	}
	
	thpool_jobqueue_empty(tp_p);
	
	/* Dealloc */
	free(tp_p->threads);                                                   /* DEALLOC threads             */
	free(tp_p->jobqueue->queueSem);                                        /* DEALLOC job queue semaphore */
	free(tp_p->jobqueue);                                                  /* DEALLOC job queue           */
	free(tp_p);                                                            /* DEALLOC thread pool         */
}



/* =================== JOB QUEUE OPERATIONS ===================== */



/* Initialise queue */
int thpool_jobqueue_init(thpool_t* tp_p){
	tp_p->jobqueue=(thpool_jobqueue*)malloc(sizeof(thpool_jobqueue));      /* MALLOC job queue */
	if (tp_p->jobqueue==NULL) return -1;
	tp_p->jobqueue->tail=NULL;
	tp_p->jobqueue->head=NULL;
	tp_p->jobqueue->jobsN=0;
	return 0;
}


/* Add job to queue */
void thpool_jobqueue_add(thpool_t* tp_p, thpool_job_t* newjob_p){ /* remember that job prev and next point to NULL */

	newjob_p->next=NULL;
	newjob_p->prev=NULL;
	
	thpool_job_t *oldFirstJob;
	oldFirstJob = tp_p->jobqueue->head;
	
	/* fix jobs' pointers */
	switch(tp_p->jobqueue->jobsN){
		
		case 0:     /* if there are no jobs in queue */
					tp_p->jobqueue->tail=newjob_p;
					tp_p->jobqueue->head=newjob_p;
					break;
		
		default: 	/* if there are already jobs in queue */
					oldFirstJob->prev=newjob_p;
					newjob_p->next=oldFirstJob;
					tp_p->jobqueue->head=newjob_p;

	}

	(tp_p->jobqueue->jobsN)++;     /* increment amount of jobs in queue */
	sem_post(tp_p->jobqueue->queueSem);
	
	int sval;
	sem_getvalue(tp_p->jobqueue->queueSem, &sval);
}


/* Remove job from queue */
int thpool_jobqueue_removelast(thpool_t* tp_p){
	thpool_job_t *oldLastJob;
	oldLastJob = tp_p->jobqueue->tail;
	
	/* fix jobs' pointers */
	switch(tp_p->jobqueue->jobsN){
		
		case 0:     /* if there are no jobs in queue */
					return -1;
					break;
		
		case 1:     /* if there is only one job in queue */
					tp_p->jobqueue->tail=NULL;
					tp_p->jobqueue->head=NULL;
					break;
					
		default: 	/* if there are more than one jobs in queue */
					oldLastJob->prev->next=NULL;               /* the almost last item */
					tp_p->jobqueue->tail=oldLastJob->prev;
					
	}
	
	(tp_p->jobqueue->jobsN)--;
	
	int sval;
	sem_getvalue(tp_p->jobqueue->queueSem, &sval);
	return 0;
}


/* Get first element from queue */
thpool_job_t* thpool_jobqueue_peek(thpool_t* tp_p){
	return tp_p->jobqueue->tail;
}

/* Remove and deallocate all jobs in queue */
void thpool_jobqueue_empty(thpool_t* tp_p){
	
	thpool_job_t* curjob;
	curjob=tp_p->jobqueue->tail;
	
	while(tp_p->jobqueue->jobsN){
		tp_p->jobqueue->tail=curjob->prev;
		free(curjob);
		curjob=tp_p->jobqueue->tail;
		tp_p->jobqueue->jobsN--;
	}
	
	/* Fix head and tail */
	tp_p->jobqueue->tail=NULL;
	tp_p->jobqueue->head=NULL;
}