pool: add ABT_POOL_RANDWS

Now all the builtin pools are FIFO, which is known to be inefficient for
divide-and-conquer task paralleism.  This PR implements ABT_POOL_RANDWS
to provide a good pool implementation for this type of parallelism.

src/include/abt.h.in

@@ -522,7 +522,31 @@ enum ABT_pool_kind {
      *
      * If the user does not know how \c ABT_POOL_FIFO_WAIT works,
      * \c ABT_POOL_FIFO is recommended. */
-    ABT_POOL_FIFO_WAIT
+    ABT_POOL_FIFO_WAIT,
+    /**
+     * Random work-stealing pool which is often adopted by fine-grained task
+     * parallel runtime systems such as Cilk.
+     *
+     * Create push                       Non-create push (e.g., yield/resume)
+     *            \                     /
+     *             (head) <- <- <- (tail)
+     *            /                     \
+     *   Local pop                       Remote pop
+     *
+     * Specifically, if one of the following flags is set to ABT_pool_context, a
+     * work unit is pushed to the head.
+     *  - ABT_POOL_CONTEXT_OP_THREAD_CREATE
+     *  - ABT_POOL_CONTEXT_OP_THREAD_CREATE_TO
+     *  - ABT_POOL_CONTEXT_OP_THREAD_REVIVE
+     *  - ABT_POOL_CONTEXT_OP_THREAD_REVIVE_TO
+     * Otherwise, a work unit is pushed to the tail.
+     *
+     * If ABT_POOL_CONTEXT_OWNER_SECONDARY is set to ABT_pool_context, a work
+     * unit is popped from the tail.  Otherwise, a work unit is popped from the
+     * head.
+     *
+     * The user is recommended to use this pool with ABT_SCHED_RANDWS. */
+    ABT_POOL_RANDWS
 };
 
 /**

src/include/abti.h

@@ -609,6 +609,11 @@ ABTI_pool_get_fifo_wait_def(ABT_pool_access access,
                             ABTI_pool_required_def *p_required_def,
                             ABTI_pool_optional_def *p_optional_def,
                             ABTI_pool_deprecated_def *p_deprecated_def);
+ABTU_ret_err int
+ABTI_pool_get_randws_def(ABT_pool_access access,
+                         ABTI_pool_required_def *p_required_def,
+                         ABTI_pool_optional_def *p_optional_def,
+                         ABTI_pool_deprecated_def *p_deprecated_def);
 void ABTI_pool_print(ABTI_pool *p_pool, FILE *p_os, int indent);
 void ABTI_pool_reset_id(void);
 

src/pool/Makefile.mk

@@ -9,4 +9,5 @@ abt_sources += \
 	pool/pool.c \
 	pool/pool_config.c \
 	pool/pool_user_def.c \
+	pool/randws.c \
 	pool/thread_queue.h

src/pool/pool.c

@@ -1411,6 +1411,11 @@ ABTU_ret_err int ABTI_pool_create_basic(ABT_pool_kind kind,
                 ABTI_pool_get_fifo_wait_def(access, &required_def,
                                             &optional_def, &deprecated_def);
             break;
+        case ABT_POOL_RANDWS:
+            abt_errno =
+                ABTI_pool_get_randws_def(access, &required_def, &optional_def,
+                                         &deprecated_def);
+            break;
         default:
             abt_errno = ABT_ERR_INV_POOL_KIND;
             break;