[SOLVED] 程序代写 COMP5426 Distributed

COMP5426 Distributed
Distributed M

dard defines

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MPI defines a standard library for message-passing that can be used to develop portable message- passing programs using either C or Fortran
the semantics of a core set of library routines
both the syntax
ations of MPI are availabl
cial paralle
l computers

Subroutines for Communication
 No locks because
e or point-to-point: Send and Receive
Collectives all processor get together to
 Move data: Broadcast, Scatter/gather
 Compute and move: sum, product, max, prefix sum, … of data on many processors
Synchronization
many processes? Which one
variables to
? Any messages

Standard itself:
All MP HTML
I official r
Other information
http://www.mcs.anl
eleases, in
.gov/research/pr
both postscript and
ojects/mpi
pointers tutorials
to lots of stuff, including , a FAQ, other MPI page

MPI_Finalize
MPI_Comm_size
The minimal set
MPI_Comm_rank Determines t

Passing Interface
Determines the nu
Sends a message.
Receives a
of processes.
of calling

MPI_Init is called
purpose is to initialize the
MPI_Finalize is called at the end of the computat performs various clean-up tasks to terminate the environment
The prototypes of
int MPI_Init(int *argc, cha
int MPI_Finalize()
MPI_Init a
any calls to other
MPI environment
lso strips off any MPI related command-l
All MPI routines, data-types, “MPI_”. The return code for MPI_SUCCESS
and constants are prefixed successful completion is
ion, a MPI

A communicator defines set of processes that ar with each other
e transfer
ion about communic
in variables of type MPI_Comm Communicators are used as arguments to all
A process can belong to many dif overlapping) communication doma
MPI defines a default
MPI_COMM_WORLD processes
a communication domain – e allowed to communicate
PI routines
ation doma
ins is stored
ferent (possibly ins
municator called
which includes all the

The calling
int MPI_Co
up to the size of
s and data
Information
The MPI_Comm_size and MPI_Comm_rank func are used to determine the number of processes the label of the calling process, respectively
(MPI_Comm co
int MPI_Comm_rank(MPI_Comm comm, int *rank) The rank of a process is an integer that ranges from
SPMD – Single Program and Multiple Data
All processes run the same program on different
– Process’s
mmunicator minus one
id) is esse

#include
main(int argc, char *argv[])
int npes, myrank name_len;
char processor_name[MPI_MAX_PROCESSOR_N MPI_Init(&argc, &argv); MPI_Comm_size(MPI_COMM_WORLD, &npes); MPI_Comm_rank(MPI_COMM_WORLD, &myrank); MPI_Get_processor_name(processor_name, &name_len); printf(“Hello world from %s, rank %d/%d
”,
processor_name, myrank, npes);
_Finalize();
compile the program using mpicc:
mpicc –o myprog myprog.c
run the program using mpirun:
mpirun –np 5 myprog

The basic fun
MPI are the MPI_Send
int MPI_Recv(void
Data are presented b
MPI provides equivalent datatypes for all
is done for
portability reasons
and MPI_Recv, respectively
quences of these routines are as fol
int MPI_Send(void *buf, int count,
MPI_Datatype datatype, int MPI_Comm comm)
*buf, int coun
y triplet {buf, count,
The dest/source is receive/send process’s rank in a
communicator comm (default
t, MPI_Dat
int source, int tag, MPI_Comm comm,
MPI_Status
is MPI_COMM_WORLD)
and receiving messages in
C datatypes.

MPI_SHORT MPI_INT MPI_LONG
MPI_UNSIGNED
MPI_UNSIGNED
MPI_UNSIGNED
MPI_UNSIGNED
MPI_DOUBLE MPI_LONG_DOUBLE MPI_BYTE
MPI_PACKED
C Datatype
signed short signed int signed long int
double long doub
ed long int

The message-tag can take
If ta any t
ecification
Messages are sent with an accompanying user-defined integer tag, to assist the receiving process in identifying the message
to the MPI defined constant MPI_TAG_UB
If source is set to MPI_ANY_SOURCE, then any process of the communication domain can be the
g is set to MPI_ANY_T ag are accepted
ranging from z
of wildcard arguments fo
then messages

The corresponding data
typedef struct MPI_Status {
PI_SOURCE;
PI_TAG; PI_ERROR
I_Get_count(MPI_
On the receiving end, the status variable ca to get information about the MPI_Recv ope
structure contains:
et_count function returns t
count of data items received
MPI_Datatype
datatype, i
n be used ration
he precise

The process is blocked in the MP
On the receive side, the message must be of length equal to or less than the length field specified
 For receives the remote data has been safely copied into the receive buffer
s the send
buffer can be safely
by the user without impacting the message transfer
I function

int a[10],
b[10], myrank;
MPI_Status status;
MPI_Comm_rank(MPI_COMM_WORLD, &myrank);
if (myrank == 0) {
MPI_Recv(b, 10,
MPI_Send(a, 10,
MPI_Recv(a, 10, MPI_INT, 0, 1,
MPI_Send(b, 10,
I_Recv is blockin
MPI_INT, 1, 2, M
MPI_INT, 1, 1, MPI_COMM
MPI_INT, 0, 2, MPI_COMM_WORLD);

… MPI MPI MPI
In the following code, process i r from process i – 1 (module the nu and sends a message to process i
number of processes)
int a[10], b[10],
_Comm_size(MPI_COMM_WORLD, &npes); _Comm_rank(MPI_COMM_WORLD, &myrank); _Recv(b, 10, MPI_INT, (myrank-1+npes)%npes, 1, M
&status); _Send(a, 10, MPI
_INT, (myrank+1)%npe
have a deadlock
eceives a message mber of processes)
+ 1 (modulo the
s, 1, MPI_C
OMM_WORLD);

Avoiding D
int a[10], b[1
MPI_Status
_Comm_size(MPI_COMM_WORLD, &npes);
MPI_Comm_rank(MPI_COMM_WORLD, &myra
if (myrank%2 == 1) {
MPI_Send(a, 10, MPI_INT, (myrank+1)%npes, 1, MPI_COMM MPI_Recv(b, 10, MPI_INT, (myrank-1+npes)%npes, 1,
MPI_COMM_WORLD, &status);
MPI_Recv(b, 10, MPI_I
MPI_COMM_W
wait to avoid dea
NT, (myrank-1+npes)%npes, 1,
MPI_Send(a, 10, MPI_INT, (myrank+1)%npes, 1, MPI_COMM

Sending and Receivin
ages Simultaneo
To exchange messages, MPI provides the following
MPI_Sendrecv(void *sendbuf, int sendcount, MPI_Datatype senddatatype, int dest, int sendtag,
void *recvbuf, int recvcount, MPI_Datatype recvdatatype,
int source, int recvtag, MPI_Comm comm, MPI_Status *status)
The arguments include functions. If we wish t receive, we can use:
arguments to the send and receive
o use the same buffer for both send and
MPI_Sendrecv_replace(void *buf, int count, MPI_Datatype datatype, int dest, int sendtag, int so int recvtag, MPI_Comm comm, MPI_Status *status)

Non-Blockin
MPI Functions:
MPI_ISend,
MPI_Request *request: a so called opaque object, which identifies communication operations and
matches the operation tha
communication with the op
t initiates the
eration that termin

Non-Blockin
Functions:
MPI_Wait blocks
until operation is finish

Non-Blockin
unctions: MPI_Testsome,
*array_of_reques
MPI_Status
tsome(int incount,
int MPI_Testsome(int incount, MPI_Request *array_of_requests, int *outcount, int *array_of_indices, MPI_Status *array_of_statuses)
ts, int *outcount, int
*array_of_statuses)
Tests or waits until at least one of the operations with active handles in the list have completed
Needs an array of requests (also indices and statuses) multiple Isend/Irecv operations
MPI_Waitso
MPI_Request
*array_of_indices,

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