add thread name, fix warning in the example

thread name is good for both profiling and debuging
also htop can turn on the option 'Show custom thread names' in 'Display
options'
the warning in example is ‘pthread_self’ [-Wimplicit-function-declaration]

example.c

@@ -12,6 +12,7 @@
  * */
 
 #include <stdio.h>
+#include <pthread.h>
 #include "thpool.h"
 
 

thpool.c

@@ -16,6 +16,7 @@
 #include <pthread.h>
 #include <errno.h>
 #include <time.h> 
+#include <sys/prctl.h>
 
 #include "thpool.h"
 
@@ -335,6 +336,10 @@ static void thread_hold () {
 * @return nothing
 */
 static void* thread_do(struct thread* thread_p){
+	/* Set thread name for profiling and debuging */
+	char thread_name[128] = {0};
+	sprintf(thread_name, "thread-pool-%d", thread_p->id);
+	prctl(PR_SET_NAME, thread_name);
 
 	/* Assure all threads have been created before starting serving */
 	thpool_* thpool_p = thread_p->thpool_p;