<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML3.2 EN"> <HTML> <HEAD> <META NAME="GENERATOR" CONTENT="DOCTEXT"> <TITLE>MPI_Allgather</TITLE> </HEAD> <BODY BGCOLOR="FFFFFF"> <A NAME="MPI_Allgather"><H1>MPI_Allgather</H1></A> Gathers data from all tasks and distribute the combined data to all tasks <H2>Synopsis</H2> <PRE> int MPI_Allgather(void *sendbuf, int sendcount, MPI_Datatype sendtype, void *recvbuf, int recvcount, MPI_Datatype recvtype, MPI_Comm comm) </PRE> <H2>Input Parameters</H2> <DL> <DT><B>sendbuf </B><DD>starting address of send buffer (choice) <DT><B>sendcount </B><DD>number of elements in send buffer (integer) <DT><B>sendtype </B><DD>data type of send buffer elements (handle) <DT><B>recvcount </B><DD>number of elements received from any process (integer) <DT><B>recvtype </B><DD>data type of receive buffer elements (handle) <DT><B>comm </B><DD>communicator (handle) </DL> <P> <H2>Output Parameter</H2> <DL><DT><B>recvbuf </B> <DD> address of receive buffer (choice) </DL> <P> <H2>Notes</H2> The MPI standard (1.0 and 1.1) says that <BR> <P> <BR> <P> The jth block of data sent from each proess is received by every process and placed in the jth block of the buffer <TT>recvbuf</TT>. <BR> <P> <BR> <P> This is misleading; a better description is <BR> <P> <BR> <P> The block of data sent from the jth process is received by every process and placed in the jth block of the buffer <TT>recvbuf</TT>. <BR> <P> <BR> <P> This text was suggested by Rajeev Thakur and has been adopted as a clarification by the MPI Forum. <P> <H2>Thread and Interrupt Safety</H2> <P> This routine is thread-safe. This means that this routine may be safely used by multiple threads without the need for any user-provided thread locks. However, the routine is not interrupt safe. Typically, this is due to the use of memory allocation routines such as <TT>malloc </TT>or other non-MPICH runtime routines that are themselves not interrupt-safe. <P> <H2>Notes for Fortran</H2> All MPI routines in Fortran (except for <TT>MPI_WTIME</TT> and <TT>MPI_WTICK</TT>) have an additional argument <TT>ierr</TT> at the end of the argument list. <TT>ierr </TT>is an integer and has the same meaning as the return value of the routine in C. In Fortran, MPI routines are subroutines, and are invoked with the <TT>call</TT> statement. <P> All MPI objects (e.g., <TT>MPI_Datatype</TT>, <TT>MPI_Comm</TT>) are of type <TT>INTEGER </TT>in Fortran. <P> <H2>Errors</H2> <P> All MPI routines (except <TT>MPI_Wtime</TT> and <TT>MPI_Wtick</TT>) return an error value; C routines as the value of the function and Fortran routines in the last argument. Before the value is returned, the current MPI error handler is called. By default, this error handler aborts the MPI job. The error handler may be changed with <TT>MPI_Comm_set_errhandler</TT> (for communicators), <TT>MPI_File_set_errhandler</TT> (for files), and <TT>MPI_Win_set_errhandler</TT> (for RMA windows). The MPI-1 routine <TT>MPI_Errhandler_set</TT> may be used but its use is deprecated. The predefined error handler <TT>MPI_ERRORS_RETURN</TT> may be used to cause error values to be returned. Note that MPI does <EM>not</EM> guarentee that an MPI program can continue past an error; however, MPI implementations will attempt to continue whenever possible. <P> <DL><DT><B>MPI_ERR_COMM </B> <DD> Invalid communicator. A common error is to use a null communicator in a call (not even allowed in <TT>MPI_Comm_rank</TT>). </DL> <DL><DT><B>MPI_ERR_COUNT </B> <DD> Invalid count argument. Count arguments must be non-negative; a count of zero is often valid. </DL> <DL><DT><B>MPI_ERR_TYPE </B> <DD> Invalid datatype argument. May be an uncommitted MPI_Datatype (see <TT>MPI_Type_commit</TT>). </DL> <DL><DT><B>MPI_ERR_BUFFER </B> <DD> Invalid buffer pointer. Usually a null buffer where one is not valid. </DL> <P><B>Location:</B>allgather.c<P> </BODY></HTML>