From 024fd4b82f983776eddeb35b7168d8e4d07af3bf Mon Sep 17 00:00:00 2001
From: Grzegorz Kowal <grzegorz@amuncode.org>
Date: Fri, 12 Nov 2021 08:07:59 -0300
Subject: [PATCH] MESH: Add a common workspace to be used in various modules.

This workspace removes the necessity of allocating the local subroutine
arrays. It is allocated once in initialize_mesh() and can be used in any
place of the code. By default, the size of this workspace is controlled
by the block dimensions, the number of variables, and the simulation
dimension, but it can be controlled by a parameter 'workspace_size'.

Additionally, there is a logical flag 'work_in_use' exported from this
module to permit the verification if the workspace is currently in use.

Signed-off-by: Grzegorz Kowal <grzegorz@amuncode.org>
---
 sources/mesh.F90 | 49 +++++++++++++++++++++++++++++++++++++++---------
 1 file changed, 40 insertions(+), 9 deletions(-)

diff --git a/sources/mesh.F90 b/sources/mesh.F90
index fb4d570..1f5bbcd 100644
--- a/sources/mesh.F90
+++ b/sources/mesh.F90
@@ -43,27 +43,36 @@ module mesh
   integer            , save :: imi, ims, img, imu, ima, imp, imr
 #endif /* PROFILE */
 
-! file handler for the mesh statistics
+! the handler of the mesh statistics file
 !
   integer, save :: funit   = 11
 
-! flag indicating that the block structure or distribution has changed
+! the size of the common workspace
+!
+  integer, save :: nwork   = 0
+
+! the flag indicating that the workspace is in use
+!
+  logical, save :: work_in_use = .false.
+
+! the flag indicating that the block structure or distribution has changed
 !
   logical, save :: changed = .true.
 
-! dimensions of the temporary array used in the block prolongation
+! the dimensions of the temporary array used in the block prolongation
 !
   integer, dimension(3), save :: pm = 1
 
-! by default everything is private
+! the common workspace to use for local arrays
 !
+  real(kind=8), dimension(:), allocatable, target :: work
+
   private
 
-! declare public subroutines
-!
   public :: initialize_mesh, finalize_mesh
   public :: generate_mesh, update_mesh
   public :: redistribute_blocks, store_mesh_stats
+  public :: work, work_in_use
 
 !- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
 !
@@ -91,8 +100,12 @@ module mesh
 !
   subroutine initialize_mesh(nrun, status)
 
-    use coordinates, only : ni => ncells, ng => nghosts, toplev
-    use mpitools   , only : master, nprocs
+    use coordinates    , only : nn => bcells, ni => ncells, ng => nghosts
+    use coordinates    , only : toplev
+    use equations      , only : nf
+    use iso_fortran_env, only : error_unit
+    use mpitools       , only : master, nprocs
+    use parameters     , only : get_parameter
 
     implicit none
 
@@ -102,6 +115,8 @@ module mesh
     character(len=64) :: fn
     integer           :: l, n
 
+    character(len=*), parameter :: loc = 'MESH::initialize_mesh()'
+
 !-------------------------------------------------------------------------------
 !
 #ifdef PROFILE
@@ -158,10 +173,24 @@ module mesh
 
     end if ! master
 
-! prepare dimensions of the prolongation array
+! prepare the dimensions of the prolongation array
 !
     pm(1:NDIMS) = 2 * (ni + ng)
 
+! get the requested size of the workspace
+!
+    call get_parameter('workspace_size', nwork)
+    nwork = max(nwork, (2 * NDIMS + 1) * nf * nn**NDIMS)
+
+! allocate the workspace
+!
+    allocate(work(nwork), stat=status)
+
+    if (status /= 0) then
+      write(error_unit,"('[',a,']: ',a)") trim(loc)                            &
+                      , "Cannot allocate the common workspace!"
+    end if
+
 #ifdef PROFILE
     call stop_timer(imi)
 #endif /* PROFILE */
@@ -201,6 +230,8 @@ module mesh
 
     if (master) close(funit)
 
+    if (allocated(work)) deallocate(work)
+
 #ifdef PROFILE
     call stop_timer(imi)
 #endif /* PROFILE */