BARRIER(3PVM) PVM Version 3.4 BARRIER(3PVM)NAME
pvm_barrier - Blocks the calling process until all processes in a group have called it.
SYNOPSIS
C int info = pvm_barrier( char *group, int count )
Fortran call pvmfbarrier( group, count, info )
PARAMETERS
group Character string group name. The group must exist and the calling process must be a member of the group.
count Integer specifying the number of group members that must call pvm_barrier before they are all released. Though not required, count
is expected to be the total number of members of the specified group.
info Integer status code returned by the routine. Values less than zero indicate an error.
DESCRIPTION
The routine pvm_barrier blocks the calling process until count members of the group have called pvm_barrier. The count argument is
required because processes could be joining the given group after other processes have called pvm_barrier. Thus PVM doesn't know how many
group members to wait for at any given instant. Although count can be set less, it is typically the total number of members of the group.
So the logical function of the pvm_barrier call is to provide a group synchronization. During any given barrier call all participating
group members must call barrier with the same count value. Once a given barrier has been successfully passed, pvm_barrier can be called
again by the same group using the same group name.
If pvm_barrier is successful, info will be 0. If some error occurs then info will be < 0.
EXAMPLES
C:
inum = pvm_joingroup( "worker" );
.
.
info = pvm_barrier( "worker", 5 );
Fortran:
CALL PVMFJOINGROUP( "shakers", INUM )
COUNT = 10
CALL PVMFBARRIER( "shakers", COUNT, INFO )
ERRORS
These error conditions can be returned by pvm_barrier
PvmSysErr
pvmd was not started or has crashed.
PvmBadParam
giving a count < 1.
PvmNoGroup
giving a non-existent group name.
PvmNotInGroup
calling process is not in specified group.
SEE ALSO pvm_joingroup(3PVM)
30 August, 1993 BARRIER(3PVM)
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SCATTER(3PVM) PVM Version 3.4 SCATTER(3PVM)NAME
pvm_scatter - Sends to each member of a group a section of an array from a specified member of the group.
SYNOPSIS
C int info = pvm_scatter( void *result, void *data,
int count, int datatype, int msgtag,
char *group, int rootginst)
Fortran call pvmfscatter(result, data, count, datatype,
msgtag, group, rootginst, info)
PARAMETERS
result Pointer to the starting address of an array of length count of datatype which will be overwritten by the message from the specified
root member of the group.
data On the root this is a pointer to the starting address of an array datatype of local values which are to be distributed to the mem-
bers of the group. If n is 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.
count Integer specifying the number of elements of datatype to be sent to each member of the group from 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 different
kinds of messages.
group Character string group name of an existing group.
rootginst
Integer instance number of group member who performs the scatter of its array to the members of the group.
info Integer status code returned by the routine. Values less than zero indicate an error.
DESCRIPTION
pvm_scatter() performs a scatter of data from the specified root member of the group to each of the members of the group, including itself.
All group members must call pvm_scatter(), each receives a portion of the data array from the root in their local result array. It is as
if the root node sends to the ith member of the group count elements from its array data starting at offset i*count from the beginning of
the data array. And, it is as if, each member of the group performs a corresponding receive of count values of datatype into its 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, typically starting with an offset of 1.
The current algorithm is very simple and robust. A future implementation may make more efficient use of the architecture to allow greater
parallelism.
EXAMPLES
C:
info = pvm_scatter(&getmyrow, &matrix, 10, PVM_INT,
msgtag, "workers", rootginst);
Fortran:
CALL PVMFSCATTER(GETMYCOLUMN, MATRIX, COUNT, INTEGER4,
& MTAG, 'workers', ROOT, INFO)
ERRORS
These error conditions can be returned by pvm_scatter
PvmNoInst
Calling task is not in the group
PvmBadParam
The datatype specified is not appropriate
PvmSysErr
Pvm system error
SEE ALSO pvm_bcast(3PVM), pvm_barrier(3PVM), pvm_psend(3PVM)
21 April, 1994 SCATTER(3PVM)