Nonblocking mail_receive, fix proc_kill scheduling issues

kernel/proc/mail.c

@@ -147,3 +147,51 @@ void proc_mail_receive (struct proc* proc, struct proc_mail* mail, struct resche
   /* nothing to receive */
   proc_sq_suspend (proc, &mail->recv_sq, &mail->resource->lock, fr, rctx);
 }
+
+bool proc_mail_receive_nonblock (struct proc* proc, struct proc_mail* mail,
+                                 struct reschedule_ctx* rctx, void* recv_buffer, size_t recv_size) {
+  uint64_t fp, fr, fssq;
+
+  spin_lock (&proc->lock, &fp);
+  proc->mail_recv_buffer = recv_buffer;
+  proc->mail_recv_size = recv_size;
+  spin_unlock (&proc->lock, fp);
+
+  spin_lock (&mail->resource->lock, &fr);
+
+  /* consume mesg if available */
+  if (mail->packets_count > 0) {
+    struct mail_packet* packet = list_entry (mail->packets, struct mail_packet, packets_link);
+    list_remove (mail->packets, &packet->packets_link);
+    mail->packets_count--;
+
+    memcpy (recv_buffer, packet->packet_buffer, min (recv_size, packet->packet_size));
+    free (packet->packet_buffer);
+    free (packet);
+
+    /* check for suspended sender */
+    spin_lock (&mail->send_sq.lock, &fssq);
+
+    struct list_node_link* node = mail->send_sq.proc_list;
+
+    if (node != NULL) {
+      struct proc_sq_entry* sq_entry = list_entry (node, struct proc_sq_entry, sq_link);
+      struct proc* resumed_proc = sq_entry->proc;
+
+      spin_unlock (&mail->send_sq.lock, fssq);
+      spin_unlock (&mail->resource->lock, fr);
+
+      proc_sq_resume (resumed_proc, sq_entry, rctx);
+      return true;
+    }
+
+    spin_unlock (&mail->send_sq.lock, fssq);
+    spin_unlock (&mail->resource->lock, fr);
+
+    return true;
+  }
+
+  spin_unlock (&mail->resource->lock, fr);
+
+  return false;
+}