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Example Programs

Example Programs

world.f

include `/totem/pvm3/include/fpvm3.h'

c Example program illustrating the use of PVM 3

integer mytid, who, numt, info, msgtype

integer hellotid

c Enroll this program in PVM

call pvmfmytid( mytid )

c Start another task ie spawn hello

call pvmfspawn(`hello', PVMDEFAULT, `*', 1,

hellotid, numt)

c Send a message to other task to begin processing,

c ie intialise the send buffer, pack the message, and

c send the message

call pvmfinitsend(PVMDEFAULT,info)

call pvmfpack(INTEGER4, mytid, 1,1,info)

msgtype = 1

call pvmfsend(hellotid,msgtype, info)

c Receive message back from task ie a blocking

c receive waiting for a message of type 2

msgtype = 2

call pvmfrecv(-1,msgtype, info)

c Unpack the message and test its contents.

call pvmfunpack(INTEGER4, who, 1, 1, info)

if (who .ne. hellotid) then

print * , 'World: incorrect TID received.'

endif

c Continue with processing and exit pvm

print*, 'World'

print*, `end of processing'

call pvmfexit()

stop

end

hello.f

include `/totem/pvm3/include/fpvm3.h'

c Example program illustrating the use of PVM 3

integer mytid, parenttid, info, msgtype

c Enroll program in PVM and find the tid of the parent

call pvmfmytid(mytid)

call pvmfparent(parenttid)

c A blocking receive waiting for a message of type 1,

c unpacks it and carries out processing

msgtype = 1

call pvmfrecv(-1, msgtype, info)

call pvmfunpack(INTEGER4, who, 1, 1, info)

if (who .ne. parenttid)

& print *, 'Hello: incorrect TID received.'

print*, `Hello'

c Sends a message back to the parent and exits pvm

call pvmfinitsend(PVMDEFAULT,info)

call pvmfpack(INTEGER4, mytid, 1,1,info)

msgtype = 2

call pvmfsend(parenttid, msgtype, info)

call pvmfexit()

stop

end

PVMFINITSEND()

CALL PVMFINITSEND (ENCODING, BUFID)

• encoding - specifies the next message's encoding scheme where the options are:
  • PvmDataDefault ie XDR encoding used by default as PVM cannot know if a user is going to add a heterogeneous machine before this message

  • PvmDataRaw ie no encoding used when it is known that the receiving machine understands the native format

  • PvmDataInPlace ie specifies that data be left in place during packing

• bufid - integer returned containing the message buffer identifier. Values less than zero indicate an error.

PVMFPACK()

CALL PVMFPACK(WHAT, XP, NITEM, STRIDE,

INFO)

• what - specifies the type of data being packed
  
  

• xp - pointer to the start of a block of bytes, can be of any data type but must match the corresponding unpack data type

• nitem - total number of items to be packed (not the number of bytes)

• stride - the stride to be used when packing the items

• info - integer status code returned by the routine, values less than zero indicate an error.

CALL PVMFPACK(INTEGER4, NSIZE, 1, 1, INFO)

C Packing Functions

• Each data type is packed by a different function:

also

pkbyte, pkcplx, pkdcplx, pkdouble, pkfloat,

pklong, pkshort, pkstr

• Arguments are:
  • a pointer to the first item

  • nitem - number of items

  • stride - stride/step through the data

  • pvm_pkstr - packs a null terminated string (no nitem or stride)

• Can be called multiple times in any combination

• C structures must be packed by element

• Complexity of packed message is unlimited

• Unpacking should occur in the same order (and size) as packing (not strictly necessary but good programming practice)

• Similar functions exist for unpacking

PVMFSEND()

CALL PVMFSEND(TID, MSGTAG, INFO)

• tid - integer task identifier of destination process

• msgtag - integer message tag supplied by the user, should be >= 0

• info - integer status code returned by the routine, values less than zero indicate an error.

CALL PVMFSEND(TID, MSGTAG, INFO)

PVMFRECV()

CALL PVMFRECV(TID, MSGTAG, BUFID)

• tid - integer identifier of sending process supplied by the user, a -1 in this argument matches any tid ie. a wildcard.

• msgtag - integer message tag supplied by the user, should be >= 0, allows the user's program to distinguish between different kinds of messages. A -1 in this argument matches any msgtag ie. a wildcard.

• bufid - integer returns the value of the new active receive buffer identifier. Values less than zero indicate an error.

CALL PVMFRECV(-1, 4, BUFID)

PVMFBUFINFO()

• Returns information about the message in the nominated buffer. Useful when the message was received with wildcards for TID and msgtag

MSGTAG, TID, INFO)

• BUFID - integer buffer id returned by pvmfrecv

• BYTES - length of the last message

• MSGTAG - integer message tag

• TID - TID of sending process

• INFO - return status

PVMFSPAWN()

CALL PVMFSPAWN(TASK, FLAG, WHERE,

NTASK, TIDS, NUMT)

• task - character string containing the executable file name of the PVM process to be started

• flag - integer specifying spawn options eg PvmTaskDefault which means PVM can choose any machine to start task

• where - character string specifying where to start the PVM process

• ntask - integer specifying the number of copies of the executable to start up

• tids - array of length at least ntask which contains the tids of the PVM process started by this pvmfspawn call

• numt - integer returning the actual number of tasks started, values less than 0 indicate a system error. A positive value less than ntask also indicates a partial failure

CALL PVMFSPAWN(`nodeprog', FLAG, `sioux-atm',

1, TIDS(3), NUMT)

PVMFMCAST()

CALL PVMFMCAST(NTASK, TIDS, MSGTAG, INFO)

• ntask - specifies the number of tasks to be sent a message

• tids - array of length at least ntask which contains the tids of the tasks to be sent the message

• msgtag - integer message tag supplied by the user, should be >= 0

• info - integer status code returned by the routine, values less than zero indicate an error.

Compilation

• During compilation programs need to be linked to the PVM library and the Fortran header file included:

-Lpvm-root/lib/pvm-architecture -lfpvm3 -lpvm3

or

cc -Ipvm-include-directory -o hello hello.c

-Lpvm-root/lib/pvm-architecture -lpvm3

• Two environment variables PVM_ROOT and PVM_ARCH are provided to point to the location of PVM on the system. Hence
  • f77 -I$PVM_ROOT/include -o hello hello.f -L$PVM_ROOT/lib/$PVM_ARCH -lfpvm3 -lpvm3

Execution

• The PVM console command spawn searches for the executable programs in 2 places
  • in the user's directory - ~/pvm3/bin/$PVM_ARCH

  • in $PVM_ROOT/bin/$PVM_ARCH

• Therefore compiled programs should be moved to ~/pvm3/bin/$PVM_ARCH

Practical

• Compilation and execution of program hello and world