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MPI: Difference between revisions
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The Message Passing Interface (MPI) is, strictly speaking, a ''standard'' describing a set of subroutines, functions, objects, ''etc.'', with which one can write parallel programs in a distributed memory environment. Many different ''implementations'' of the standard have been produced, such as Open MPI, MPICH, and MVAPICH. The standard describes how MPI should be called from Fortran, C, and C++ languages, but unofficial "bindings" can be found for several other languages. | The Message Passing Interface (MPI) is, strictly speaking, a ''standard'' describing a set of subroutines, functions, objects, ''etc.'', with which one can write parallel programs in a distributed memory environment. Many different ''implementations'' of the standard have been produced, such as Open MPI, Intel MPI, MPICH, and MVAPICH. The standard describes how MPI should be called from Fortran, C, and C++ languages, but unofficial "bindings" can be found for several other languages. Note that MPI 3.0 dropped official C++ bindings but instead you can use the C bindings from C++, or Boost MPI. | ||
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Each MPI program must include the relevant header file or use the relevant module (<tt>mpi.h</tt> for C/C++, <tt>mpif.h</tt>, <tt>use mpi</tt>, or <tt>use mpi_f08</tt> for Fortran, where <tt>mpif.h</tt> is strongly discouraged and <tt>mpi_f08</tt> recommended for new Fortran 2008 code), and be compiled and linked against the desired MPI implementation. Most MPI implementations provide a handy script, often called a ''compiler wrapper'', that handles all set-up issues with respect to <code>include</code> and <code>lib</code> directories, linking flags, ''etc.'' Our examples will all use these compiler wrappers: | Each MPI program must include the relevant header file or use the relevant module (<tt>mpi.h</tt> for C/C++, <tt>mpif.h</tt>, <tt>use mpi</tt>, or <tt>use mpi_f08</tt> for Fortran, where <tt>mpif.h</tt> is strongly discouraged and <tt>mpi_f08</tt> recommended for new Fortran 2008 code), and be compiled and linked against the desired MPI implementation. Most MPI implementations provide a handy script, often called a ''compiler wrapper'', that handles all set-up issues with respect to <code>include</code> and <code>lib</code> directories, linking flags, ''etc.'' Our examples will all use these compiler wrappers: | ||
* C language wrapper: <tt>mpicc</tt> | * C language wrapper: <tt>mpicc</tt> | ||
* Fortran: <tt>mpif90</tt> | * Fortran: <tt>mpifort</tt> (recommended) or <tt>mpif90</tt> | ||
* C++: <tt>mpiCC</tt> | * C++: <tt>mpiCC</tt> | ||
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<tt>MPI_Recv</tt> works in much the same way as <tt>MPI_Send</tt>. Referring to the function prototypes below, <tt>message</tt> is now a pointer to an allocated buffer of sufficient size to store <tt>count</tt> instances of <tt>datatype</tt>, to be received from process <tt>rank</tt>. <tt>MPI_Recv</tt> takes one additional argument, <tt>status</tt>, which should, in C, be a reference to an allocated <tt>MPI_Status</tt> structure, and, in Fortran, be an array of <tt>MPI_STATUS_SIZE</tt> integers. Upon return it will contain some information about the received message. Although we will not make use of it in this tutorial, the argument must be present. | <tt>MPI_Recv</tt> works in much the same way as <tt>MPI_Send</tt>. Referring to the function prototypes below, <tt>message</tt> is now a pointer to an allocated buffer of sufficient size to store <tt>count</tt> instances of <tt>datatype</tt>, to be received from process <tt>rank</tt>. <tt>MPI_Recv</tt> takes one additional argument, <tt>status</tt>, which should, in C, be a reference to an allocated <tt>MPI_Status</tt> structure, and, in Fortran, be an array of <tt>MPI_STATUS_SIZE</tt> integers or, for <tt>mpi_f08</tt>, a derived <tt>TYPE(MPI_Status)</tt> variable. Upon return it will contain some information about the received message. Although we will not make use of it in this tutorial, the argument must be present. | ||
</translate> | </translate> | ||
<tabs> | <tabs> | ||
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implicit none | implicit none | ||
use | use mpi | ||
integer, parameter :: BUFMAX=81 | integer, parameter :: BUFMAX=81 | ||
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call MPI_FINALIZE(ierr) | call MPI_FINALIZE(ierr) | ||
end program phello3 | |||
}} | |||
</tab> | |||
<tab name="Fortran 2008"> | |||
{{File | |||
|name=phello3.f90 | |||
|lang="fortran" | |||
|contents= | |||
program phello3 | |||
implicit none | |||
use mpi_f08 | |||
integer, parameter :: BUFMAX=81 | |||
character(len=BUFMAX) :: outbuf, inbuf, tmp | |||
integer :: rank, num_procs | |||
integer :: sendto, recvfrom | |||
type(MPI_Status) :: status | |||
call MPI_Init() | |||
call MPI_Comm_rank(MPI_COMM_WORLD, rank) | |||
call MPI_Comm_size(MPI_COMM_WORLD, num_procs) | |||
outbuf = 'Hello, world! from process ' | |||
write(tmp,'(i2)') rank | |||
outbuf = outbuf(1:len_trim(outbuf)) // tmp(1:len_trim(tmp)) | |||
write(tmp,'(i2)') num_procs | |||
outbuf = outbuf(1:len_trim(outbuf)) // ' of ' // tmp(1:len_trim(tmp)) | |||
sendto = mod((rank + 1), num_procs) | |||
recvfrom = mod(((rank + num_procs) - 1), num_procs) | |||
if (MOD(rank,2) == 0) then | |||
call MPI_Send(outbuf, BUFMAX, MPI_CHARACTER, sendto, 0, MPI_COMM_WORLD) | |||
call MPI_Recv(inbuf, BUFMAX, MPI_CHARACTER, recvfrom, 0, MPI_COMM_WORLD, status) | |||
else | |||
call MPI_RECV(inbuf, BUFMAX, MPI_CHARACTER, recvfrom, 0, MPI_COMM_WORLD, status) | |||
call MPI_SEND(outbuf, BUFMAX, MPI_CHARACTER, sendto, 0, MPI_COMM_WORLD) | |||
endif | |||
print *, 'Process', rank, ': Process', recvfrom, ' said:', inbuf | |||
call MPI_Finalize() | |||
end program phello3 | end program phello3 | ||