eval: Fix jobwait() to process multiple jobs concurrently

The new event processing architecture changed `jobwait()` semantics: Only one
job is processed at time since process_wait only focuses on one queue.

This fixes the problem with a few changes:

- Allow the event queue polled by `process_wait` to be overriden by a new
  argument.
- Allow the parent queue to be overriden with `queue_replace_parent`
- Create a temporary queue that serves as the parent for all jobs passed to
  `jobwait()`

3 files changed, 18 insertions, 8 deletions

diff --git a/src/nvim/event/loop.c b/src/nvim/event/loop.c
index 1a50ec0d9a..3d3288f858 100644
--- a/src/nvim/event/loop.c
+++ b/src/nvim/event/loop.c
@@ -22,7 +22,7 @@ void loop_init(Loop *loop, void *data)
   loop->uv.data = loop;
   loop->children = kl_init(WatcherPtr);
   loop->children_stop_requests = 0;
-  loop->events = queue_new_parent(on_put, loop);
+  loop->events = queue_new_parent(loop_on_put, loop);
   loop->fast_events = queue_new_child(loop->events);
   uv_signal_init(&loop->uv, &loop->children_watcher);
   uv_timer_init(&loop->uv, &loop->children_kill_timer);
@@ -59,7 +59,7 @@ void loop_poll_events(Loop *loop, int ms)
   queue_process_events(loop->fast_events);
 }
 
-static void on_put(Queue *queue, void *data)
+void loop_on_put(Queue *queue, void *data)
 {
   Loop *loop = data;
   // Sometimes libuv will run pending callbacks(timer for example) before
diff --git a/src/nvim/event/process.c b/src/nvim/event/process.c
index 54dbc11a03..81d4e690c3 100644
--- a/src/nvim/event/process.c
+++ b/src/nvim/event/process.c
@@ -152,7 +152,7 @@ void process_close_err(Process *proc) FUNC_ATTR_NONNULL_ALL
 ///         indistinguishable from the process returning -1 by itself. Which
 ///         is possible on some OS. Returns -2 if an user has interruped the
 ///         wait.
-int process_wait(Process *proc, int ms) FUNC_ATTR_NONNULL_ALL
+int process_wait(Process *proc, int ms, Queue *events) FUNC_ATTR_NONNULL_ARG(1)
 {
   // The default status is -1, which represents a timeout
   int status = -1;
@@ -162,10 +162,14 @@ int process_wait(Process *proc, int ms) FUNC_ATTR_NONNULL_ALL
     return proc->status;
   }
 
+  if (!events) {
+    events = proc->events;
+  }
+
   // Increase refcount to stop the exit callback from being called(and possibly
   // being freed) before we have a chance to get the status.
   proc->refcount++;
-  LOOP_PROCESS_EVENTS_UNTIL(proc->loop, proc->events, ms,
+  LOOP_PROCESS_EVENTS_UNTIL(proc->loop, events, ms,
       // Until...
       got_int ||             // interrupted by the user
       proc->refcount == 1);  // job exited
@@ -179,10 +183,10 @@ int process_wait(Process *proc, int ms) FUNC_ATTR_NONNULL_ALL
     if (ms == -1) {
       // We can only return if all streams/handles are closed and the job
       // exited.
-      LOOP_PROCESS_EVENTS_UNTIL(proc->loop, proc->events, -1,
+      LOOP_PROCESS_EVENTS_UNTIL(proc->loop, events, -1,
           proc->refcount == 1);
     } else {
-      LOOP_PROCESS_EVENTS(proc->loop, proc->events, 0);
+      LOOP_PROCESS_EVENTS(proc->loop, events, 0);
     }
   }
 
@@ -191,9 +195,9 @@ int process_wait(Process *proc, int ms) FUNC_ATTR_NONNULL_ALL
     // resources
     status = interrupted ? -2 : proc->status;
     decref(proc);
-    if (proc->events) {
+    if (events) {
       // the decref call created an exit event, process it now
-      queue_process_events(proc->events);
+      queue_process_events(events);
     }
   } else {
     proc->refcount--;
diff --git a/src/nvim/event/queue.c b/src/nvim/event/queue.c
index 3f03dd444e..19eca14144 100644
--- a/src/nvim/event/queue.c
+++ b/src/nvim/event/queue.c
@@ -152,6 +152,12 @@ bool queue_empty(Queue *queue)
   return QUEUE_EMPTY(&queue->headtail);
 }
 
+void queue_replace_parent(Queue *queue, Queue *new_parent)
+{
+  assert(queue_empty(queue));
+  queue->parent = new_parent;
+}
+
 static Event queue_remove(Queue *queue)
 {
   assert(!queue_empty(queue));