Add hts_tpool_worker_id() API

This returns a numeric value from 0 to nthreads-1 corresponding to the
current running thread, or -1 if unthreaded or the thread does not
correspond to one allocated to this pool.

It may be used to associate data to a thread rather than to a job.
For example maintaining one open file handle per thread spawned.

htslib/thread_pool.h

@@ -115,6 +115,14 @@ HTSLIB_EXPORT
 int hts_tpool_size(hts_tpool *p);
 
 
+/// Return the worker ID index, from 0 to nthreads-1.
+/**
+ * @param p         Thread pool
+ * @return          The worker index (0..ntheads-1) or -1 if not found
+ */
+HTSLIB_EXPORT
+int hts_tpool_worker_id(hts_tpool *pool);
+
 /// Add an item to the work pool.
 /**
  * @param p     Thread pool

thread_pool.c

@@ -51,17 +51,21 @@ static void hts_tpool_process_detach_locked(hts_tpool *p,
 
 //#define DEBUG
 
-#ifdef DEBUG
-static int worker_id(hts_tpool *p) {
-    int i;
+// Return the worker ID index, from 0 to nthreads-1.
+// Return <0 on error, but this shouldn't be possible
+int hts_tpool_worker_id(hts_tpool *p) {
+    if (!p)
+        return -1;
     pthread_t s = pthread_self();
+    int i;
     for (i = 0; i < p->tsize; i++) {
         if (pthread_equal(s, p->t[i].tid))
             return i;
     }
     return -1;
 }
 
+#ifdef DEBUG
 void DBG_OUT(FILE *fp, char *fmt, ...) {
     va_list args;
     va_start(args, fmt);
@@ -95,7 +99,7 @@ static int hts_tpool_add_result(hts_tpool_job *j, void *data) {
     pthread_mutex_lock(&q->p->pool_m);
 
     DBG_OUT(stderr, "%d: Adding result to queue %p, serial %"PRId64", %d of %d\n",
-            worker_id(j->p), q, j->serial, q->n_output+1, q->qsize);
+            hts_tpool_worker_id(j->p), q, j->serial, q->n_output+1, q->qsize);
 
     if (--q->n_processing == 0)
         pthread_cond_signal(&q->none_processing_c);
@@ -129,9 +133,9 @@ static int hts_tpool_add_result(hts_tpool_job *j, void *data) {
            || q->next_serial == INT_MAX); // ... unless flush in progress.
     if (r->serial == q->next_serial) {
         DBG_OUT(stderr, "%d: Broadcasting result_avail (id %"PRId64")\n",
-                worker_id(j->p), r->serial);
+                hts_tpool_worker_id(j->p), r->serial);
         pthread_cond_broadcast(&q->output_avail_c);
-        DBG_OUT(stderr, "%d: Broadcast complete\n", worker_id(j->p));
+        DBG_OUT(stderr, "%d: Broadcast complete\n", hts_tpool_worker_id(j->p));
     }
 
     pthread_mutex_unlock(&q->p->pool_m);
@@ -603,7 +607,7 @@ static void *tpool_worker(void *arg) {
             pthread_mutex_unlock(&p->pool_m);
 
             DBG_OUT(stderr, "%d: Processing queue %p, serial %"PRId64"\n",
-                    worker_id(j->p), q, j->serial);
+                    hts_tpool_worker_id(j->p), q, j->serial);
 
             if (hts_tpool_add_result(j, j->func(j->arg)) < 0)
                 goto err;
@@ -625,13 +629,13 @@ static void *tpool_worker(void *arg) {
  shutdown:
     pthread_mutex_unlock(&p->pool_m);
 #ifdef DEBUG
-    fprintf(stderr, "%d: Shutting down\n", worker_id(p));
+    fprintf(stderr, "%d: Shutting down\n", hts_tpool_worker_id(p));
 #endif
     return NULL;
 
  err:
 #ifdef DEBUG
-    fprintf(stderr, "%d: Failed to add result\n", worker_id(p));
+    fprintf(stderr, "%d: Failed to add result\n", hts_tpool_worker_id(p));
 #endif
     // Hard failure, so shutdown all queues
     pthread_mutex_lock(&p->pool_m);