1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
|
.\" $Id: pvm_gather.3,v 1.1 1996/09/23 22:01:18 pvmsrc Exp $
.TH GATHER 3PVM "21 April, 1994" "" "PVM Version 3.4"
.SH NAME
pvm_gather \- A specified member of the group receives messages
from each member of the group and gathers these messages into
a single array.
.SH SYNOPSIS
.nf
.ft B
C int info = pvm_gather( void *result, void *data,
.br
int count, int datatype, int msgtag,
.br
char *group, int rootginst)
.br
Fortran call pvmfgather(result, data, count, datatype,
.br
msgtag, group, rootginst, info)
.fi
.SH PARAMETERS
.IP result 0.8i
On the root this is a
pointer to the starting address of an array
.I 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
.I datatype
should be of length at least
n*\fIcount\fR.
This argument is meaningful only on the root.
.br
.IP data
For each group member this is a pointer to the starting
address of an array of length
.I count
of
.I datatype
which will be sent to the specified root member of the group.
.br
.IP count
Integer specifying the number of elements of
.I datatype
to be sent by each member of the group to the root.
.br
.IP datatype
Integer specifying the type of the entries in the result and data arrays.
(See below for defined types.)
.IP 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.
.br
.IP group
Character string group name of an existing group.
.br
.IP rootginst
Integer instance number of group member who performs the
gather of the messages from the members of the group.
.br
.IP info
Integer status code returned by the routine.
Values less than zero indicate an error.
.SH DESCRIPTION
.I pvm_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
.I data
of length
.I count
of
.I datatype
to the root which accumulates these messages into its
.I result
array.
It is as if the root receives
.I count
elements of
.I datatype
from the ith member of the group and places these values in its
.I result
array starting with offset i*\fIcount\fR from the beginning of the
.I result
array.
The root task is identified by its instance number in the group.
.PP
C and Fortran defined
.I datatypes
are:
.nf
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
.fi
.PP
In using the scatter and gather routines, keep in mind that
C stores multidimensional arrays in row order,
typically starting with an initial index of 0; whereas,
Fortran stores arrays in column order,
typically starting with an offset of 1.
.PP
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.
.PP
The current algorithm is very simple and robust. A future implementation
may make more efficient use of the architecture to allow greater
parallelism.
.SH EXAMPLES
.nf
C:
info = pvm_gather(&getmatrix, &myrow, 10, PVM_INT,
msgtag, "workers", rootginst);
.sp
Fortran:
CALL PVMFGATHER(GETMATRIX, MYCOLUMN, COUNT, INTEGER4,
& MTAG, 'workers', ROOT, INFO)
.fi
.SH ERRORS
These error conditions can be returned by
.I pvm_gather
.IP PvmNoInst
Calling task is not in the group
.IP PvmBadParam
The datatype specified is not appropriate
.IP PvmSysErr
Pvm system error
.PP
.SH SEE ALSO
pvm_bcast(3PVM),
pvm_barrier(3PVM),
pvm_psend(3PVM)
|
