Smart polling implemented

README.md

@@ -17,6 +17,7 @@ This is an updated and heavily refactored version of my original threadpool. The
   * Synchronisation control from the user (pause/resume/wait)
   * Thorough testing for memory leaks and race conditions
   * Cleaner and more opaque API
+  * Smart polling - polling interval changes on-the-fly
 
 
 ## Compiling

tests/src/wait.c

@@ -33,8 +33,6 @@ int main(int argc, char *argv[]){
 	int num_threads   = strtol(argv[2], &p, 10);
 	int wait_each_job = strtol(argv[3], &p, 10);
 
-	printf("%d\n", wait_each_job);
-
 	threadpool thpool = thpool_init(num_threads);
 	
 	int n;

thpool.c

@@ -2,8 +2,7 @@
  * Author:       Johan Hanssen Seferidis
  * License:	     MIT
  * Description:  Library providing a threading pool where you can add
- *               work. For an example on usage refer to the main file
- *               found in the same package
+ *               work. For usage, check the thpool.h file or README.md
  *
  *//** @file thpool.h *//*
  * 
@@ -20,7 +19,8 @@
 
 #include "thpool.h"
 
-#define POLLING_INTERVAL 1
+#define MAX_NANOSEC 999999999
+#define CEIL(X) ((X-(int)(X)) > 0 ? (int)(X+1) : (int)(X))
 
 static volatile int threads_keepalive;
 static volatile int threads_on_hold;
@@ -42,9 +42,9 @@ typedef struct bsem {
 
 /* Job */
 typedef struct job{
+	struct job*  prev;                   /* pointer to previous job   */
 	void*  (*function)(void* arg);       /* function pointer          */
 	void*  arg;                          /* function's argument       */
-	struct job*       prev;              /* pointer to previous job   */
 } job;
 
 
@@ -70,6 +70,7 @@ typedef struct thread{
 typedef struct thpool_{
 	thread**   threads;                  /* pointer to threads        */
 	int        num_threads_alive;        /* threads currently alive   */
+	int        num_threads_working;      /* threads currently working */
 	pthread_mutex_t  thcount_lock;       /* used for thread count etc */
 	jobqueue*  jobqueue_p;               /* pointer to the job queue  */    
 } thpool_;
@@ -123,6 +124,7 @@ struct thpool_* thpool_init(int num_threads){
 		exit(1);
 	}
 	thpool_p->num_threads_alive   = 0;
+	thpool_p->num_threads_working = 0;
 
 	/* Initialise the job queue */
 	if (jobqueue_init(thpool_p)==-1){
@@ -174,10 +176,47 @@ int thpool_add_work(thpool_* thpool_p, void *(*function_p)(void*), void* arg_p){
 }
 
 
-/* Wait until all jobs in queue have finished */
+/* Wait until all jobs have finished */
 void thpool_wait(thpool_* thpool_p){
-	while (thpool_p->jobqueue_p->len) {
-		sleep(POLLING_INTERVAL);
+
+	/* Continuous polling */
+	double timeout = 1.0;
+	time_t start, end;
+	double tpassed;
+	time (&start);
+	while (tpassed < timeout && 
+			(thpool_p->jobqueue_p->len || thpool_p->num_threads_working))
+	{
+		time (&end);
+		tpassed = difftime(end,start);
+	}
+
+	/* Exponential polling */
+	long init_nano =  1; /* MUST be above 0 */
+	long new_nano;
+	double multiplier =  1.01;
+	int  max_secs   = 20;
+	
+	struct timespec polling_interval;
+	polling_interval.tv_sec  = 0;
+	polling_interval.tv_nsec = init_nano;
+	
+	while (thpool_p->jobqueue_p->len || thpool_p->num_threads_working)
+	{
+		nanosleep(&polling_interval, NULL);
+		if ( polling_interval.tv_sec < max_secs ){
+			new_nano = CEIL(polling_interval.tv_nsec * multiplier);
+			polling_interval.tv_nsec = new_nano % MAX_NANOSEC;
+			if ( new_nano > MAX_NANOSEC ) {
+				polling_interval.tv_sec ++;
+			}
+		}
+		else break;
+	}
+	
+	/* Fall back to max polling */
+	while (thpool_p->jobqueue_p->len || thpool_p->num_threads_working){
+		sleep(max_secs);
 	}
 }
 
@@ -305,6 +344,10 @@ static void* thread_do(struct thread* thread_p){
 
 		if (threads_keepalive){
 			
+			pthread_mutex_lock(&thpool_p->thcount_lock);
+			thpool_p->num_threads_working++;
+			pthread_mutex_unlock(&thpool_p->thcount_lock);
+			
 			/* Read job from queue and execute it */
 			void*(*func_buff)(void* arg);
 			void*  arg_buff;
@@ -319,6 +362,10 @@ static void* thread_do(struct thread* thread_p){
 				free(job_p);
 			}
 			
+			pthread_mutex_lock(&thpool_p->thcount_lock);
+			thpool_p->num_threads_working--;
+			pthread_mutex_unlock(&thpool_p->thcount_lock);
+
 		}
 	}
 	pthread_mutex_lock(&thpool_p->thcount_lock);
@@ -390,6 +437,7 @@ static void jobqueue_push(thpool_* thpool_p, struct job* newjob){
 					
 	}
 	thpool_p->jobqueue_p->len++;
+	
 	bsem_post(thpool_p->jobqueue_p->has_jobs);
 }
 

thpool.h

@@ -72,7 +72,11 @@ int thpool_add_work(threadpool, void *(*function_p)(void*), void* arg_p);
  * Once the queue is empty and all work has completed, the calling thread
  * (probably the main program) will continue.
  * 
- * Polling is used in wait. By default the polling interval is one second.
+ * Smart polling is used in wait. The polling is initially 0 - meaning that
+ * there is virtually no polling at all. If after 1 seconds the threads
+ * haven't finished, the polling interval starts growing exponentially 
+ * untill it reaches max_secs seconds. Then it jumps down to a maximum polling
+ * interval assuming that heavy processing is being used in the threadpool.
  *
  * @example
  *