GATHER(3PVM) PVM Version 3.4 GATHER(3PVM)NAMEpvm_gather - A specified member of the group receives messages from
each member of the group and gathers these messages into a single
array.
SYNOPSIS
C int info = pvm_gather( void *result, void *data,
int count, int datatype, int msgtag,
char *group, int rootginst)
Fortran call pvmfgather(result, data, count, datatype,
msgtag, group, rootginst, info)
PARAMETERS
result On the root this is a pointer to the starting address of an
array datatype of local values which are to be accumulated from
the members of the group. If n if the number of members in the
group, then this array of datatype should be of length at least
n*count. This argument is meaningful only on the root.
data For each group member this is a pointer to the starting address
of an array of length count of datatype which will be sent to
the specified root member of the group.
count Integer specifying the number of elements of datatype to be
sent by each member of the group to the root.
datatype
Integer specifying the type of the entries in the result and
data arrays. (See below for defined types.)
msgtag Integer message tag supplied by the user. msgtag should be >=
0. It allows the user's program to distinguish between differ‐
ent kinds of messages.
group Character string group name of an existing group.
rootginst
Integer instance number of group member who performs the gather
of the messages from the members of the group.
info Integer status code returned by the routine. Values less than
zero indicate an error.
DESCRIPTIONpvm_gather() performs a send of messages from each member of the group
to the specified root member of the group. All group members must call
pvm_gather(), each sends its array data of length count of datatype to
the root which accumulates these messages into its result array. It is
as if the root receives count elements of datatype from the ith member
of the group and places these values in its result array starting with
offset i*count from the beginning of the result array. The root task
is identified by its instance number in the group.
C and Fortran defined datatypes are:
C datatypes FORTRAN datatypes
-----------------------------------
PVM_BYTE BYTE1
PVM_SHORT INTEGER2
PVM_INT INTEGER4
PVM_FLOAT REAL4
PVM_CPLX COMPLEX8
PVM_DOUBLE REAL8
PVM_DCPLX COMPLEX16
PVM_LONG
In using the scatter and gather routines, keep in mind that C stores
multidimensional arrays in row order, typically starting with an ini‐
tial index of 0; whereas, Fortran stores arrays in column order, typi‐
cally starting with an offset of 1.
Note: pvm_gather() does not block. If a task calls pvm_gather and
then leaves the group before the root has called pvm_gather an error
may occur.
The current algorithm is very simple and robust. A future implementa‐
tion may make more efficient use of the architecture to allow greater
parallelism.
EXAMPLES
C:
info = pvm_gather(&getmatrix, &myrow, 10, PVM_INT,
msgtag, "workers", rootginst);
Fortran:
CALL PVMFGATHER(GETMATRIX, MYCOLUMN, COUNT, INTEGER4,
& MTAG, 'workers', ROOT, INFO)
ERRORS
These error conditions can be returned by pvm_gather
PvmNoInst
Calling task is not in the group
PvmBadParam
The datatype specified is not appropriate
PvmSysErr
Pvm system error
SEE ALSOpvm_bcast(3PVM), pvm_barrier(3PVM), pvm_psend(3PVM)
21 April, 1994 GATHER(3PVM)
