mpi

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mpi
Documentation
Examples
- Master/worker example
- Master/worker implemented with collective operations
About this egg

Documentation

MPI is a popular standard for distributed-memory parallel programming. It offers both point-to-point message passing and group communication operations (broadcast, scatter/gather, etc).

Open MPI is an implementation of the MPI standard that combines technologies and resources from several other projects (FT-MPI, LA-MPI, LAM/MPI, and PACX-MPI) in order to build the best MPI library available.

The Chicken MPI egg provides a Scheme interface to a large subset of the MPI 1.2 procedures for communication. It is based on the Ocaml MPI library by Xavier Leroy. The mpi library has been tested with Open MPI versions 1.2.4 - 1.10.1.

Initialization and time procedures

MPI:initprocedure: Initializes the MPI execution environment. This routine must be called before any other MPI routine. MPI can be initialized at most once.

MPI:spawnprocedure: Spawns MAXPROCS identical copies of the MPI program specified by COMMAND and returns an intercommunicator and a vector of status values. ARGUMENTS is a list of command-line arguments. LOCATIONS is a list of string pairs (HOST * WDIR) that tell MPI the host and working directory where to start processes.

MPI:finalizeprocedure: Terminates the MPI execution environment.

MPI:wtimeprocedure: Returns the number of seconds representing elapsed wall-clock time on the calling process.

Handling of communicators

MPI:comm?procedure: Returns true if OBJ is an MPI communicator object, false otherwise.

MPI:get-comm-world:procedure: Returns the default communicator created by MPI_Init; the group associated with this communicator contains all processes.

MPI:comm-sizeprocedure: Returns the size of the group associated with communicator COMM.

MPI:comm-rankprocedure: Returns the rank of the calling process in communicator COMM.

MPI:comm-equal?procedure: Returns true if the two given communicators are for identical groups, false otherwise.

MPI:comm-splitprocedure: Creates new communicators based on colors and keys.

MPI:comm-createprocedure: Creates a new communicator with communication group that spans all processes in GROUP and a new context. See the procedures in subsection Handling of communication groups for information on how to create process group objects.

MPI:make-cartprocedure: Creates a new communicator with Cartesian topology information. Argument DIMS is an SRFI-4 s32vector that contains the number of dimensions of the Cartesian grid. Argument PERIODS is an SRFI-4 s32vector of the same length as DIMS that indicates if the grid is periodic (1) or not (0) in each dimension. Argument REORDER is a boolean value that indicates whether process ranking may be reordered.

MPI:make-dimsprocedure: Creates a division of processes in a Cartesian grid. Argument NNODES is the number of nodes in the grid. Argument NDIMS is the number of Cartesian dimensions. The return values is an SRFI-4 s32vector.

MPI:cart-coordsprocedure: Determines process coordinates in Cartesian topology, given a rank in the group. The return value is an SRFI-4 s32vector of length NDIMS (the number of dimensions in the Cartesian topology).

Handling of communication groups

MPI:group?procedure: Returns true if OBJ is an MPI group object, false otherwise.

MPI:comm-groupprocedure: Returns the group associated with the given communicator.

MPI:group-sizeprocedure: Returns the size of the group GROUP.

MPI:group-rankprocedure: Returns the rank of the calling process in the given group.

MPI:group-translate-ranksprocedure: Translates the ranks of processes in one group to those in another group. The return value is an SRFI-4 s32vector.

MPI:group-unionprocedure

MPI:group-differenceprocedure

MPI:group-intersectionprocedure

MPI:group-inclprocedure: Produces a group by reordering an existing group and taking only members with the given ranks. Argument RANKS is an SRFI-4 s32vector.

MPI:group-exclprocedure: Produces a group by reordering an existing group and taking only members that do not have the given ranks. Argument RANKS is an SRFI-4 s32vector.

MPI datatypes

MPI:datatype?procedure: Returns true if `OBJ` is an MPI datatype object, false otherwise.

MPI:type-extentprocedure: Returns the extent and lower bound of an MPI data type.

MPI:type-sizeprocedure

Returns the size of a datatype.

MPI:type-char
MPI:type-int
MPI:type-fixnum
MPI:type-flonum
MPI:type-byte
MPI:type-s8
MPI:type-u8
MPI:type-s16
MPI:type-u16
MPI:type-s32
MPI:type-u32
MPI:type-f32
MPI:type-f64

Predefined MPI data types.

MPI:make-type-structprocedure: Given a gield count, field lengths and field types, creates and returns a new MPI structure data type with the given fields.

Point-to-point communication

Most communication procedures in this library come in several flavors, for fixnums, integers, floating point numbers, bytevectors, and for each of the SRFI-4 homogeneous vector types.

MPI:sendprocedure
MPI:send-TYPEprocedure: Performs a standard-mode blocking send. Argument DEST is the rank of the destination process. Argument TAG is integer message tag. Argument DATATYPE is an MPI datatype object. TYPE is one of the following: fixnum, int, flonum, bytevector, s8vector, u8vector, s16vector, u16vector, s32vector, u32vector, f32vector, f64vector

MPI:receiveprocedure
MPI:receive-TYPEprocedure: Performs a standard-mode blocking receive. Argument DEST is the rank of the destination process. Argument TAG is integer message tag. Argument LENGTH is present only in the vector procedures. TYPE is one of the following: fixnum, int, flonum, bytevector, s8vector, u8vector, s16vector, u16vector, s32vector, u32vector, f32vector, f64vector

MPI:probeprocedure: Checks for an incoming message. This is a blocking call that returns only after a matching message is found. Argument DATATYPE is an MPI datatype object. Argument SOURCE can be MPI:any-source. Argument TAG can be MPI:any-tag.

Group communication

MPI:barrierprocedure: Barrier synchronization.

MPI:broadcastprocedure
MPI:broadcast-TYPEprocedure: Broadcasts a message from the process with rank root to all other processes of the group. Argument DATATYPE is an MPI datatype object. TYPE is one of the following: fixnum, int, flonum, bytevector, s8vector, u8vector, s16vector, u16vector, s32vector, u32vector, f32vector, f64vector

MPI:scatterprocedure
MPI:scatter-TYPEprocedure: Sends data from the root process to all processes in a group, and returns the data received by the calling process. Argument SENDCOUNT is the number of elements sent to each process. Argument DATATYPE is an MPI datatype object. Argument DATA is only required at the root process. All other processes can invoke this procedure with (void) as DATA. TYPE is one of the following: int, flonum, bytevector, s8vector, u8vector, s16vector, u16vector, s32vector, u32vector, f32vector, f64vector

MPI:scattervprocedure
MPI:scatterv-TYPEprocedure: Sends variable-length data from the root process to all processes in a group, and returns the data received by the calling process. Argument DATATYPE is an MPI datatype object. Argument DATA is only required at the root process, and is a list of values of type TYPE, where each element of the list is sent to the process of corresponding rank. All other processes can invoke this procedure with (void) as DATA. TYPE is one of the following: int, flonum, bytevector, s8vector, u8vector, s16vector, u16vector, s32vector, u32vector, f32vector, f64vector

MPI:gatherprocedure
MPI:gather-TYPEprocedure: Gathers data from a group of processes, where each process send data of the same length. Argument SENDCOUNT is the number of data elements being sent by each process. Argument DATATYPE is an MPI datatype object. TYPE is one of the following: int, flonum, bytevector, s8vector, u8vector, s16vector, u16vector, s32vector, u32vector, f32vector, f64vector

MPI:gathervprocedure
MPI:gatherv-TYPEprocedure: Gathers data from a group of processes, where each process can send data of variable length. Argument DATATYPE is an MPI datatype object. TYPE is one of the following: int, flonum, bytevector, s8vector, u8vector, s16vector, u16vector, s32vector, u32vector, f32vector, f64vector

MPI:allgatherprocedure
MPI:allgather-TYPEprocedure: Gathers data of variable length from all processes and distributes it to all processes. Argument DATATYPE is an MPI datatype object. TYPE is one of the following: int, flonum, bytevector, s8vector, u8vector, s16vector, u16vector, s32vector, u32vector, f32vector, f64vector

MPI:reduce-TYPEprocedure: Reduces values on all processes within a group, using a global reduce operation, and return the result at the root process. OP is one of the following: MPI:i_max, MPI:i_min, MPI:i_sum, MPI:i_prod, MPI:i_land, MPI:i_lor, MPI:i_xor (integer operations); and MPI:f_max, MPI:f_min, MPI:f_sum, MPI:f_prod (floating point operations). TYPE is one of the following: int, flonum, bytevector, s8vector, u8vector, s16vector, u16vector, s32vector, u32vector, f32vector, f64vector

MPI:allreduce-TYPEprocedure: Reduces values on all processes within a group, using a global reduce operation, and return the result at each process. OP is one of the following: MPI:i_max, MPI:i_min, MPI:i_sum, MPI:i_prod, MPI:i_land, MPI:i_lor, MPI:i_xor (integer operations); and MPI:f_max, MPI:f_min, MPI:f_sum, MPI:f_prod (floating point operations). TYPE is one of the following: int, flonum, bytevector, s8vector, u8vector, s16vector, u16vector, s32vector, u32vector, f32vector, f64vector

MPI:scan-TYPEprocedure: Computes a partial reduction across the processes in a group. OP is one of the following: MPI:i_max, MPI:i_min, MPI:i_sum, MPI:i_prod, MPI:i_land, MPI:i_lor, MPI:i_xor (integer operations); and MPI:f_max, MPI:f_min, MPI:f_sum, MPI:f_prod (floating point operations). TYPE is one of the following: int, flonum, bytevector, s8vector, u8vector, s16vector, u16vector, s32vector, u32vector, f32vector, f64vector

Round-robin routines

The following variants of fold, map and for-each process lists in round-robin fashion on MPI nodes: for a given node n, only list elements whose index is a modulo of n will be processed on this node.

MPI-rr-foldprocedure

MPI-rr-mapprocedure

MPI-rr-for-eachprocedure

Examples

Master/worker example

;; Simple master/worker example
;; Can be run as follows: mpirun -np 4 csi -s master-worker.scm
;; where -np # indicates the number of processes

(import scheme (chicken base) srfi-4 mpi)

(MPI:init)

;; MPI uses objects called communicators to define how processes
;; communicate with each other.  Almost all MPI routines require a
;; communicator as an argument.  

;; `MPI:get-comm-world' returns the communicator object which can send
;; messages to all running MPI processes

(define comm-world  (MPI:get-comm-world))

;; `MPI:comm-size' returns the number of running MPI processes
;;  (including the current one)

(define size        (MPI:comm-size comm-world))

;; `MPI:comm-rank' returns the rank of the calling MPI process

(define myrank      (MPI:comm-rank comm-world))

;; We assign rank 0 to be the master process, and the rest will be
;; worker processes

(if (zero? myrank)
    (begin
      (printf "[~a/~a]: I am the master\n" myrank size)
      (let recur ((i 1))
        (if (< i size)
            (begin
              ;; Send Hello message to process of rank i
              (MPI:send-bytevector (string->blob (sprintf "Hello ~a..." i)) i 0 comm-world)
              (recur (+ 1 i)))
            ))

      (let recur ((i 1))
        (if (< i size)
             ;; Wait for a response from process of rank i
            (let ((n (blob->string (MPI:receive-bytevector i MPI:any-tag comm-world))))
              (printf "[~a/~a]: received: ~a~%" myrank size n)
              (recur (+ 1 i)))
            ))
      )
    (begin
      (printf "[~a/~a]: I am a worker\n" myrank size)
      ;; Wait for a message from the master (process 0)
      (let ((n (blob->string (MPI:receive-bytevector 0 MPI:any-tag comm-world))))
        (printf "[~a/~a]: received: ~a\n" myrank size n)
        ;; Send a response back to the master
        (MPI:send-bytevector (string->blob (sprintf "Processor ~a reporting!" myrank))
                     0 0 comm-world))
      )
    )

(MPI:finalize)

Master/worker implemented with collective operations

;; Master/worker example implemented with collective operations
;; Can be run as follows: mpirun -np 4 csi -s master-worker.scm

(import scheme (chicken base) srfi-1 srfi-4 mpi)

(MPI:init)

;; MPI uses objects called communicators to define how processes
;; communicate with each other.  Almost all MPI routines require a
;; communicator as an argument.  

;; `MPI:get-comm-world' returns the communicator object which can send
;; messages to all running MPI processes

(define comm-world  (MPI:get-comm-world))

;; `MPI:comm-size' returns the number of running MPI processes
;;  (including the current one)

(define size        (MPI:comm-size comm-world))

;; `MPI:comm-rank' returns the rank of the calling MPI process

(define myrank      (MPI:comm-rank comm-world))

;; We assign rank 0 to be the master process, and the rest will be
;; worker processes

(if (zero? myrank)
    (begin
      (printf "[~a/~a]: I am the master\n" myrank size)
      
      ;; data is a list of vectors to be sent to each process.  The
      ;; master process sends element i from the list to process i
      ;; (including itself). Note that each process must call scatterv
      ;; in order to receive its data. In this example, the master
      ;; ignores the result to its call to scatterv.

      (let ((data (list-tabulate size (lambda (i) (string->blob (sprintf "Hello ~a..." i))))))
        (MPI:scatterv-bytevector data 0 comm-world))
   
      ;; With gatherv, each process (master process included) sends
      ;; the contents of its send buffer to the master process. The
      ;; master process receives the messages and stores them in rank
      ;; order.

      (let ((v (MPI:gatherv-bytevector (string->blob "I am the master!") 0 comm-world)))
        (printf "[~a/~a]: received: ~a\n" myrank size (map blob->string v))
        ))
    (begin
      (printf "[~a/~a]: I am a worker\n" myrank size)

      ;; The worker collects its data via a call to scatterv. The data
      ;; argument is #f because the worker is not sending anything,
      ;; just receiving.

      (let ((n (blob->string (MPI:scatterv-bytevector #f 0 comm-world))))
        (printf "[~a/~a]: received: ~a\n" myrank size n)

        ;; The worker sends its result back to the master via a call to gatherv.
        (MPI:gatherv-bytevector (string->blob (sprintf "Processor ~a reporting!" myrank))
                                0 comm-world))
      )
    )

(MPI:finalize)

2.2: Ported to CHICKEN 5
2.1: Support for MPI alltoall / alltoallv operations
2.0: Added support for MPI derived datatypes
1.14: Added simple round-robin routines
1.12: Fixes to allgather-int and allgather-flonum (thanks to Peter Bex)
1.11: Test script fixes
1.9: Ensure test script returns non-zero on error (thanks to mario)
1.7: Switched to wiki documentation
1.6: Ported to Chicken 4
1.5: Added a binding for MPI:spawn
1.3: Bug fix in MPI:scatter-int
1.2: Bug fix in the meta file
1.1: Bug fixes and improvements to the regression tests
1.0: Initial release

License

Copyright 2007-2018 Ivan Raikov.

Based on the Ocaml MPI library by Xavier Leroy. 

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or (at
your option) any later version.

This program is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
General Public License for more details.

A full copy of the GPL license can be found at
<http://www.gnu.org/licenses/>.

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