diff --git a/src/engine.c b/src/engine.c
index 7287f47b40b06a691c778a5f8d3b6c0f04721564..b78956bb9ea976cfcc55a1454320ce9901801397 100644
--- a/src/engine.c
+++ b/src/engine.c
@@ -589,6 +589,9 @@ void engine_addtasks_send(struct engine *e, struct cell *ci, struct cell *cj) {
struct task *t_rho = scheduler_addtask(s, task_type_send, task_subtype_none,
2 * ci->tag + 1, 0, ci, cj, 0);
+ /* The first send should depend on the engine's send_root. */
+ scheduler_addunlock(s, e->send_root, t_xv);
+
/* The send_rho task depends on the cell's ghost task. */
scheduler_addunlock(s, ci->super->ghost, t_rho);
@@ -633,6 +636,9 @@ void engine_addtasks_recv(struct engine *e, struct cell *c, struct task *t_xv,
2 * c->tag, 0, c, NULL, 0);
t_rho = c->recv_rho = scheduler_addtask(
s, task_type_recv, task_subtype_none, 2 * c->tag + 1, 0, c, NULL, 0);
+
+ /* The first recv should depend on the engine's recv_root. */
+ scheduler_addunlock(s, e->recv_root, t_xv);
}
/* Add dependencies. */
@@ -1414,6 +1420,12 @@ void engine_maketasks(struct engine *e) {
/* Add the communication tasks if MPI is being used. */
if ((e->policy & engine_policy_mpi) == engine_policy_mpi) {
+ /* Create root tasks for send/recv. */
+ e->send_root = scheduler_addtask(&e->sched, task_type_comm_root,
+ task_subtype_none, 0, 0, NULL, NULL, 0);
+ e->recv_root = scheduler_addtask(&e->sched, task_type_comm_root,
+ task_subtype_none, 0, 0, NULL, NULL, 0);
+
/* Loop over the proxies. */
for (int pid = 0; pid < e->nr_proxies; pid++) {
diff --git a/src/engine.h b/src/engine.h
index c8b9d7a46f8c788237e3b9ba7cb9d7d0a6e1370d..9e55deb1dd39a43f7f2eb6a771430a0dcfc5a746 100644
--- a/src/engine.h
+++ b/src/engine.h
@@ -162,6 +162,9 @@ struct engine {
struct link *links;
int nr_links, size_links;
+ /* Root task for all send and recv tasks. */
+ struct task *send_root, *recv_root;
+
/* Are we talkative ? */
int verbose;
};
diff --git a/src/runner.c b/src/runner.c
index 25ffc9f2c2b9fff4596d680ef505e714c7595c07..000e4c8b136bcb3bc1184104c0a0bf617243108d 100644
--- a/src/runner.c
+++ b/src/runner.c
@@ -1212,6 +1212,8 @@ void *runner_main(void *data) {
scheduler_do_rewait((struct task *)t->ci, (struct task *)t->cj,
t->flags, t->rank);
break;
+ case task_type_comm_root:
+ break;
default:
error("Unknown task type.");
}
diff --git a/src/scheduler.c b/src/scheduler.c
index d1d343240b37f5afd5f41fecacf106b0e85f726f..bbacf24610f3803b0d7ac0d945b820f283116d8b 100644
--- a/src/scheduler.c
+++ b/src/scheduler.c
@@ -1066,7 +1066,6 @@ void scheduler_enqueue(struct scheduler *s, struct task *t) {
if (t->implicit) {
for (int j = 0; j < t->nr_unlock_tasks; j++) {
struct task *t2 = t->unlock_tasks[j];
-
if (atomic_dec(&t2->wait) == 1) scheduler_enqueue(s, t2);
}
}
diff --git a/src/task.c b/src/task.c
index 5f1475a46e4626e1f51db673d73fd84f86e6edb6..213da9510a28bd6bfea348510e373ef7bdd7d531 100644
--- a/src/task.c
+++ b/src/task.c
@@ -46,7 +46,7 @@ const char *taskID_names[task_type_count] = {
"none", "sort", "self", "pair", "sub",
"init", "ghost", "drift", "kick", "send",
"recv", "grav_pp", "grav_mm", "grav_up", "grav_down",
- "part_sort", "gpart_sort", "split_cell", "rewait"};
+ "part_sort", "gpart_sort", "split_cell", "rewait", "comm_root"};
const char *subtaskID_names[task_type_count] = {"none", "density",
"force", "grav"};
diff --git a/src/task.h b/src/task.h
index 9c0ba6087d772d7362a98bc40a838c6fa3713166..5d72f5c61c85408e6b38e78351e661decba7dba6 100644
--- a/src/task.h
+++ b/src/task.h
@@ -49,6 +49,7 @@ enum task_types {
task_type_gpart_sort,
task_type_split_cell,
task_type_rewait,
+ task_type_comm_root,
task_type_count
};