Add new example to docs (#449)

* add new job schedule example to docs

* add reference

* fix variables names and comments

Author: rafabench

docs/examples/05-job_schedule.jl

@@ -0,0 +1,133 @@
+# This example demonstrates a job scheduling through adding the
+# number 100 to every component of the vector data. The root
+# assigns one element to each worker to compute the operation.
+# When the worker is finished, the root sends another element
+# until each element is added 100
+# Inspired on
+# https://www.hpc.ntnu.no/ntnu-hpc-group/vilje/user-guide/software/mpi-and-mpi-io-training-tutorial/basic-mpi/job-queue
+
+using MPI
+
+function job_queue(data,f)
+    MPI.Init()
+
+    comm = MPI.COMM_WORLD
+    rank = MPI.Comm_rank(comm)
+    world_size = MPI.Comm_size(comm)
+    nworkers = world_size - 1
+
+    root = 0
+
+    MPI.Barrier(comm)
+    T = eltype(data)
+    N = size(data)[1]
+    send_mesg = Array{T}(undef, 1)
+    recv_mesg = Array{T}(undef, 1)
+
+    if rank == root # I am root
+
+        idx_recv = 0
+        idx_sent = 1
+
+        new_data = Array{T}(undef, N)
+        # Array of workers requests
+        sreqs_workers = Array{MPI.Request}(undef,nworkers)
+        # -1 = start, 0 = channel not available, 1 = channel available
+        status_workers = ones(nworkers).*-1
+        
+        # Send message to workers
+        for dst in 1:nworkers
+            if idx_sent > N
+                break
+            end
+            send_mesg[1] = data[idx_sent]
+            sreq = MPI.Isend(send_mesg, dst, dst+32, comm)
+            idx_sent += 1
+            sreqs_workers[dst] = sreq
+            status_workers[dst] = 0
+            print("Root: Sent number $(send_mesg[1]) to Worker $dst\n")
+        end
+
+        # Send and receive messages until all elements are added
+        while idx_recv != N
+            # Check to see if there is an available message to receive
+            for dst in 1:nworkers
+                if status_workers[dst] == 0
+                    (flag, status) = MPI.Test!(sreqs_workers[dst])
+                    if flag
+                        status_workers[dst] = 1
+                    end
+                end
+            end
+            for dst in 1:nworkers
+                if status_workers[dst] == 1
+                    ismessage, status = MPI.Iprobe(dst,dst+32, comm)
+                    if ismessage
+                        # Receives message
+                        MPI.Recv!(recv_mesg, dst, dst+32, comm)
+                        idx_recv += 1
+                        new_data[idx_recv] = recv_mesg[1]
+                        print("Root: Received number $(recv_mesg[1]) from Worker $dst\n")
+                        if idx_sent <= N
+                            send_mesg[1] = data[idx_sent]
+                            # Sends new message
+                            sreq = MPI.Isend(send_mesg, dst, dst+32, comm)
+                            idx_sent += 1
+                            sreqs_workers[dst] = sreq
+                            status_workers[dst] = 1
+                            print("Root: Sent number $(send_mesg[1]) to Worker $dst\n")
+                        end
+                    end
+                end
+            end
+        end
+        
+        for dst in 1:nworkers
+            # Termination message to worker
+            send_mesg[1] = -1
+            sreq = MPI.Isend(send_mesg, dst, dst+32, comm)
+            sreqs_workers[dst] = sreq
+            status_workers[dst] = 0
+            print("Root: Finish Worker $dst\n")
+        end
+        
+        MPI.Waitall!(sreqs_workers)
+        print("Root: New data = $new_data\n")
+    else # If rank == worker
+        # -1 = start, 0 = channel not available, 1 = channel available
+        status_worker = -1
+        while true
+            sreqs_workers = Array{MPI.Request}(undef,1)
+            ismessage, status = MPI.Iprobe(root, rank+32, comm)
+            
+            if ismessage
+                # Receives message
+                MPI.Recv!(recv_mesg, root, rank+32, comm)
+                # Termination message from root
+                if recv_mesg[1] == -1
+                    print("Worker $rank: Finish\n")
+                    break
+                end
+                print("Worker $rank: Received number $(recv_mesg[1]) from root\n")
+                # Apply function (add number 100) to array
+                send_mesg = f(recv_mesg)
+                sreq = MPI.Isend(send_mesg, root, rank+32, comm)
+                sreqs_workers[1] = sreq
+                status_worker = 0
+            end
+            # Check to see if there is an available message to receive
+            if status_worker == 0
+                (flag, status) = MPI.Test!(sreqs_workers[1])
+                if flag
+                    status_worker = 1
+                end
+            end
+        end
+    end
+    MPI.Barrier(comm)
+    MPI.Finalize()
+end
+
+f = x -> x.+100
+data = collect(1:10)
+job_queue(data,f)

docs/make.jl

@@ -7,6 +7,7 @@ EXAMPLES = [
     "Broadcast" => "examples/02-broadcast.md",
     "Reduce" => "examples/03-reduce.md",
     "Send/receive" => "examples/04-sendrecv.md",
+    "Job Scheduling" => "examples/05-job_schedule.md"
 ]
 
 examples_md_dir = joinpath(@__DIR__,"src/examples")