add deadlock solution

slides/pages/recap.md

@@ -301,7 +301,7 @@ The receive buffer must be able to fit the entire message:
 
 The MPI status object holds information about the received message.
 
-**MPI_Status status**:
+**MPI_Status status** object is a structure in C with freely accessible members:
 
 ```c
 status.MPI_SOURCE // message source rank
@@ -440,3 +440,34 @@ This tells us: <span class="text-rose-500 font-bold">Never rely on any implement
 
 </v-click>
 
+---
+title: Deadlock III
+---
+
+### Another Solution to Deadlock
+
+**Using Combined Send and Receive**:
+
+```c
+MPI_Sendrecv (
+    void *senddata,
+    int sendcount,
+    MPI_Datatype sendtype,
+    int dest,
+    int sendtag,
+    void *recvdata,
+    int recvcount,
+    MPI_Datatype recvtype,
+    int source,
+    int recvtag,
+    MPI_Comm comm,
+    MPI_Status *status
+)
+```
+
+Sends one message and receives one message (in any order) **without deadlocking(unless unmatched)**
+
+<span class="text-rose-500 font-bold">Send and receive buffers must not overlap!</span>
+
+Don't want two buffers? -> Use **MPI_Sendrecv_replace**!
+