| MPI_ALLTOALL(sendbuf, sendcount, sendtype, recvbuf, recvcount, recvtype, comm) | |
| IN sendbuf | starting address of send buffer (choice) |
| IN sendcount | number of elements sent to each process (non-negative integer) |
| IN sendtype | data type of send buffer elements (handle) |
| OUT recvbuf | address of receive buffer (choice) |
| IN recvcount | number of elements received from any process (non-negative integer) |
| IN recvtype | data type of receive buffer elements (handle) |
| IN comm | communicator (handle) |
int MPI_Alltoall(void* sendbuf, int sendcount, MPI_Datatype sendtype, void* recvbuf, int recvcount, MPI_Datatype recvtype, MPI_Comm comm)
MPI_ALLTOALL(SENDBUF, SENDCOUNT, SENDTYPE, RECVBUF, RECVCOUNT, RECVTYPE, COMM, IERROR)
MPI_ALLTOALL is an extension of MPI_ALLGATHER to the case
where each process sends distinct data to each of the receivers.
The
j-th
block sent from process i is received by process j
and is placed in the
i-th
block of recvbuf.
The type signature associated with sendcount, sendtype,
at a process must be equal to the type signature associated with
recvcount, recvtype at any other process.
This implies that the amount of data sent must be equal to the
amount of data received, pairwise between every pair of processes.
As usual, however, the type maps may be different.
If comm is an intracommunicator,
the outcome is as if each process executed a send to each
process (itself included)
with a call to,
MPI_Send(sendbuf+i· sendcount·
extent(sendtype),sendcount,sendtype,i, ...),
and a receive from every other process
with a call to,
All arguments
on all processes are significant. The argument comm
must have identical values on all processes.
The ``in place'' option for intracommunicators is specified by passing
MPI_IN_PLACE to the argument sendbuf at all processes.
In such a case, sendcount and sendtype are ignored.
The data to be sent is taken from the recvbuf and replaced by the received data.
Data sent and received must have the same type map as specified by recvcount and recvtype.
For large MPI_ALLTOALL instances,
allocating both send and receive buffers may consume too much memory.
The ``in place'' option effectively halves the application memory consumption
and is useful in situations where the data to be sent will not be used by the
sending process after the MPI_ALLTOALL exchange (e.g., in parallel
Fast Fourier Transforms).
( End of rationale.)
Users may opt to use the ``in place'' option in order to conserve memory.
Quality MPI implementations should thus strive to minimize system buffering.
( End of advice to implementors.)
When a complete exchange is executed on an intercommunication domain, thenthe number of data items sent from processes in group A to processes
in group B need not equal the number of items sent in the reverse
direction. In particular, one can have unidirectional communication
by specifying sendcount = 0 in the reverse direction.
( End of advice to users.)
int MPI_Alltoallv(void* sendbuf, int *sendcounts, int *sdispls, MPI_Datatype sendtype, void* recvbuf, int *recvcounts, int *rdispls, MPI_Datatype recvtype, MPI_Comm comm)
MPI_ALLTOALLV(SENDBUF, SENDCOUNTS, SDISPLS, SENDTYPE, RECVBUF, RECVCOUNTS, RDISPLS, RECVTYPE, COMM, IERROR)
MPI_ALLTOALLV adds flexibility to MPI_ALLTOALL in that
the location of data for the send is specified by sdispls
and the location of the placement of the data on the receive side
is specified by rdispls.
If comm is an intracommunicator, then
the
j-th
block sent from process i is received by process j
and is placed in the
i-th
block of recvbuf. These blocks need not all have the same size.
The type signature associated with
sendcounts[j], sendtype at process i must be equalto the type signature
associated with recvcounts[i], recvtype at process j.This implies that the amount of data sent must be equal to the
amount of data received, pairwise between every pair of processes.
Distinct type maps between sender and receiver are still allowed.
The outcome is as if each process sent a message to every other process
with,
MPI_Send(sendbuf+MPIupdate2.2113sdispls[i]· extent(sendtype),sendcounts[i],sendtype,i,...),
and received a message from every other process with
a call to
MPI_Recv(recvbuf+MPIupdate2.2113rdispls[i]· extent(recvtype),recvcounts[i],recvtype,i,...).
All arguments
on all processes are significant. The argument comm
must have identical values on all processes.
The ``in place'' option for intracommunicators is specified by passing
MPI_IN_PLACE to the argument sendbuf at all processes.
In such a case, sendcounts, sdispls and sendtype are ignored.
The data to be sent is taken from the recvbuf and replaced by the received data.
Data sent and received must have the same type map as specified by the recvcounts
array and the recvtype, and is taken from the locations of the receive buffer
specified by rdispls.
Specifying the ``in place'' option (which must be given on all processes)
implies that the same amount and type of data is sent and received between
any two processes in the group of the communicator.
Different pairs of processes can exchange different amounts of data.
Users must ensure that recvcounts[j] and recvtype on process
i match recvcounts[i] and recvtype on process j.
This symmetric exchange can be useful in applications where the data to be sent will
not be used by the sending process after the MPI_ALLTOALLV exchange.
( End of advice to users.)
The definitions of MPI_ALLTOALL and MPI_ALLTOALLV give as much
flexibility as one would achieve by specifying n independent,
point-to-point communications, with two exceptions: all messages use the same
datatype, and messages are scattered from (or gathered to) sequential
storage.
( End of rationale.)
Although the discussion of collective communication in terms of
point-to-point operation implies that each message is transferred directly
from sender to receiver, implementations may use a tree communication
pattern. Messages can be forwarded by intermediate nodes where they
are split (for scatter) or concatenated (for gather), if this
is more efficient.
( End of advice to implementors.)
int MPI_Alltoallw(void *sendbuf, int sendcounts[], int sdispls[], MPI_Datatype sendtypes[], void *recvbuf, int recvcounts[], int rdispls[], MPI_Datatype recvtypes[], MPI_Comm comm)
MPI_ALLTOALLW(SENDBUF, SENDCOUNTS, SDISPLS, SENDTYPES, RECVBUF, RECVCOUNTS, RDISPLS, RECVTYPES, COMM, IERROR)
{ void MPI::Comm::Alltoallw(const void* sendbuf, const int sendcounts[], const int sdispls[], const MPI::Datatype sendtypes[], void* recvbuf, const int recvcounts[], const int rdispls[], const MPI::Datatype recvtypes[]) const = 0 (binding deprecated, see Section Deprecated since MPI-2.2
) }
MPI_ALLTOALLW
is the most general form of complete exchange.Like MPI_TYPE_CREATE_STRUCT, the most general type constructor,
MPI_ALLTOALLW allows separate specification of count,
displacement and datatype. In addition, to allow maximum flexibility,
the displacement of blocks within the send and receive buffers is
specified in bytes.
If comm is an intracommunicator, then
the j-th block sent from process i is received by process
j and is placed in the i-th block of recvbuf.
These blocks need not all have the same size.
The type signature associated with
sendcounts[j], sendtypes[j] at process i must be equal
to the type signature
associated with recvcounts[i], recvtypes[i] at process j.
This implies that the amount of data sent must be equal to the
amount of data received, pairwise between every pair of processes.
Distinct type maps between sender and receiver are still allowed.
The outcome is as if each process sent a message to every other process with
MPI_Send(sendbuf+sdispls[i],sendcounts[i],sendtypes[i] ,i,...),
and received a message from every other process with a call to
MPI_Recv(recvbuf+rdispls[i],recvcounts[i],recvtypes[i] ,i,...).
All arguments on all processes are significant. The argument
comm must describe the same communicator on all processes.
Like for MPI_ALLTOALLV, the ``in place'' option for intracommunicators
is specified by passing MPI_IN_PLACE to the argument sendbuf
at all processes.
In such a case, sendcounts, sdispls and sendtypes are ignored.
The data to be sent is taken from the recvbuf and replaced by the received data.
Data sent and received must have the same type map as specified by the recvcounts
and recvtypes arrays, and is taken from the locations of the receive buffer
specified by rdispls.
If comm is an intercommunicator, then the outcome is as if
each process in group A sends a message to each process in group B,
and vice versa. The j-th send buffer of process i in group A should
be consistent with the i-th receive buffer of process j in group B,
and vice versa.
The MPI_ALLTOALLW function generalizes several MPI functions by
carefully selecting the input arguments. For example, by making all but one
process have sendcounts[i] = 0, this achieves an MPI_SCATTERW
function.
( End of rationale.)
<type> SENDBUF(*), RECVBUF(*)
INTEGER SENDCOUNT, SENDTYPE, RECVCOUNT, RECVTYPE, COMM, IERROR
{ void MPI::Comm::Alltoall(const void* sendbuf, int sendcount, const MPI::Datatype& sendtype, void* recvbuf, int recvcount, const MPI::Datatype& recvtype) const = 0 (binding deprecated, see Section Deprecated since MPI-2.2
) }
Rationale.
Advice
to implementors.
If comm is an intercommunicator, then the outcome is as if
each process in group A sends a message to each process in group B,
and vice versa. The j-th send buffer of process i in group A should
be consistent with the i-th receive buffer of process j in group B,
and vice versa.
Advice to users.
MPI_ALLTOALLV(sendbuf, sendcounts, sdispls, sendtype,
recvbuf, recvcounts, rdispls, recvtype, comm) IN sendbuf starting address of send buffer (choice) IN sendcounts non-negative
integer array (of length group size) specifying the number of elements to send to each processor IN sdispls integer array (of length group size). Entry
j specifies the displacement (relative to sendbuf from
which to take the outgoing data destined for process j IN sendtype data type of send buffer elements (handle) OUT recvbuf address of receive buffer (choice) IN recvcounts non-negative
integer array (of length group size) specifying the number of elements that can be received from
each processor IN rdispls integer array (of length group size). Entry
i specifies the displacement (relative to recvbuf at
which to place the incoming data from process i IN recvtype data type of receive buffer elements (handle) IN comm communicator (handle)
<type> SENDBUF(*), RECVBUF(*)
INTEGER SENDCOUNTS(*), SDISPLS(*), SENDTYPE, RECVCOUNTS(*), RDISPLS(*), RECVTYPE, COMM, IERROR
{ void MPI::Comm::Alltoallv(const void* sendbuf, const int sendcounts[], const int sdispls[], const MPI::Datatype& sendtype, void* recvbuf, const int recvcounts[], const int rdispls[], const MPI::Datatype& recvtype) const = 0 (binding deprecated, see Section Deprecated since MPI-2.2
) }
Advice to users.
If comm is an intercommunicator, then the outcome is as if
each process in group A sends a message to each process in group B,
and vice versa. The j-th send buffer of process i in group A should
be consistent with the i-th receive buffer of process j in group B,
and vice versa.
Rationale.
Advice
to implementors.
MPI_ALLTOALLW(sendbuf, sendcounts, sdispls, sendtypes,
recvbuf, recvcounts, rdispls, recvtypes, comm) IN sendbuf starting address of send buffer (choice) IN sendcounts non-negative integer array (of length group size) specifying the
number of elements to send to each processor IN sdispls integer array (of length group size). Entry j specifies
the displacement in bytes (relative to sendbuf) from which to take
the outgoing data destined for process j (array of integers) IN sendtypes array of datatypes (of length group size). Entry j
specifies the type of data to send to process j (array of handles) OUT recvbuf address of receive buffer (choice) IN recvcounts non-negative integer array (of length group size) specifying the
number of elements that can be received from each processor IN rdispls integer array (of length group size). Entry i specifies
the displacement in bytes (relative to recvbuf) at which to place the
incoming data from process i (array of integers) IN recvtypes array of datatypes (of length group size). Entry i
specifies the type of data received from process i (array of handles) IN comm communicator (handle)
<type> SENDBUF(*), RECVBUF(*)
INTEGER SENDCOUNTS(*), SDISPLS(*), SENDTYPES(*), RECVCOUNTS(*), RDISPLS(*), RECVTYPES(*), COMM, IERROR
Rationale.
Up: Contents
Next: Global Reduction Operations
Previous: Example using MPI_ALLGATHER
Return to MPI-2.2 Standard Index
Return to MPI Forum Home Page
(Unofficial) MPI-2.2 of September 4, 2009
HTML Generated on September 10, 2009