<meta http-equiv="Content-Type" content="text/html; charset=iso-8859-1"><font face="Default Sans Serif,Verdana,Arial,Helvetica,sans-serif" size="2">Good Afternoon,<br><br> I am working on an MPI application which needs to listen to a UDP socket connection in the background. I caught this behavior and I was curious if this is expected or if this is a potential issue. <br><br>Essentially, until you call MPI_Init_thread, the Linux socket command will return 0 for all ranks except rank 0. This seems to me like a problem. It is easy enough to fix if MPI_Init is called first, however it does not lend itself well if you want to do any initialization work before MPI is started. <br><br>Thanks for your input<br>Marvin Smith<br><br>Given the following code sample...<br><br><b>// Libraries<br>#include <mpi.h><br>#include <arpa/inet.h><br>#include <iostream><br>#include <sys/socket.h><br>#include <unistd.h><br><br>/**<br> * Main Program<br> */<br>int main( int argc, char* argv[] )<br>{<br><br> // Test Socket Command<br> std::cout << "Pre Socket: " << socket( AF_INET, SOCK_DGRAM, IPPROTO_UDP ) << std::endl;<br><br> // Initialize MPI<br> int mpi_thread_act;<br> std::cout << "MPI_Init" << std::endl;<br> MPI_Init_thread( &argc, &argv, MPI_THREAD_MULTIPLE, &mpi_thread_act );<br><br><br> // Test another socket<br> std::cout << "Post Socket: " << socket( AF_INET, SOCK_DGRAM, IPPROTO_UDP ) << std::endl;<br><br> // Finalize MPI<br> MPI_Finalize();<br><br> // Exit<br> return 0;<br>}<br><br><br></b>The application returns output this with mpirun.<br><b><br>$ mpirun -np 2 ./test-socket <br>Pre Socket: 10<br>MPI_Init<br>Pre Socket: 0<br>MPI_Init<br>Post Socket: 14<br>Post Socket: 10<br><br><br>$ mpirun -np 3 ./test-socket <br>Pre Socket: 10<br>MPI_Init<br>Pre Socket: 0<br>MPI_Init<br>Pre Socket: 0<br>MPI_Init<br>Post Socket: 14<br>Post Socket: 10<br>Post Socket: 8</b><br><br>It appears that all ranks except 0 will not create valid sockets until MPI_Init_thread is called. <br><br>I am running this code sample using Red-Hat Enterprise Linux 7.1 with mpich<br><br><br>Below is my output from mpirun<br>$ mpirun --version<br>HYDRA build details:<br> Version: 3.0.4<br> Release Date: Wed Apr 24 10:08:10 CDT 2013<br> CC: cc -m64 -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -m64 -mtune=generic -fPIC -Wl,-z,noexecstack <br> CXX: c++ -m64 -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -m64 -mtune=generic -fPIC -Wl,-z,noexecstack <br> F77: gfortran -m64 -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -m64 -mtune=generic -fPIC -Wl,-z,noexecstack <br> F90: gfortran -m64 -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -m64 -mtune=generic -fPIC -Wl,-z,noexecstack <br> Configure options: '--disable-option-checking' '--prefix=/usr' '--build=x86_64-redhat-linux-gnu' '--host=x86_64-redhat-linux-gnu' '--program-prefix=' '--disable-dependency-tracking' '--exec-prefix=/usr' '--bindir=/usr/bin' '--sbindir=/usr/sbin' '--sysconfdir=/etc' '--datadir=/usr/share' '--includedir=/usr/include' '--libdir=/usr/lib64' '--libexecdir=/usr/libexec' '--localstatedir=/var' '--sharedstatedir=/var/lib' '--mandir=/usr/share/man' '--infodir=/usr/share/info' '--enable-sharedlibs=gcc' '--enable-shared' '--enable-lib-depend' '--disable-rpath' '--enable-fc' '--with-device=ch3:nemesis' '--with-pm=hydra:gforker' '--sysconfdir=/etc/mpich-x86_64' '--includedir=/usr/include/mpich-x86_64' '--bindir=/usr/lib64/mpich/bin' '--libdir=/usr/lib64/mpich/lib' '--datadir=/usr/share/mpich' '--mandir=/usr/share/man/mpich' '--docdir=/usr/share/mpich/doc' '--htmldir=/usr/share/mpich/doc' '--with-hwloc-prefix=system' 'FC=gfortran' 'F77=gfortran' 'CFLAGS=-m64 -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -m64 -mtune=generic -fPIC -O2' 'CXXFLAGS=-m64 -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -m64 -mtune=generic -fPIC -O2' 'FCFLAGS=-m64 -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -m64 -mtune=generic -fPIC -O2' 'FFLAGS=-m64 -O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -m64 -mtune=generic -fPIC -O2' 'LDFLAGS=-Wl,-z,noexecstack ' 'MPICH2LIB_CFLAGS=-O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -m64 -mtune=generic' 'MPICH2LIB_CXXFLAGS=-O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -m64 -mtune=generic' 'MPICH2LIB_FCFLAGS=-O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -m64 -mtune=generic' 'MPICH2LIB_FFLAGS=-O2 -g -pipe -Wall -Wp,-D_FORTIFY_SOURCE=2 -fexceptions -fstack-protector-strong --param=ssp-buffer-size=4 -grecord-gcc-switches -m64 -mtune=generic' 'build_alias=x86_64-redhat-linux-gnu' 'host_alias=x86_64-redhat-linux-gnu' '--cache-file=/dev/null' '--srcdir=.' 'CC=cc' 'LIBS=-lrt -lpthread ' 'CPPFLAGS= -I/builddir/build/BUILD/mpich-3.0.4/src/mpl/include -I/builddir/build/BUILD/mpich-3.0.4/src/mpl/include -I/builddir/build/BUILD/mpich-3.0.4/src/openpa/src -I/builddir/build/BUILD/mpich-3.0.4/src/openpa/src -I/builddir/build/BUILD/mpich-3.0.4/src/mpi/romio/include'<br> Process Manager: pmi<br> Launchers available: ssh rsh fork slurm ll lsf sge manual persist<br> Topology libraries available: <br> Resource management kernels available: user slurm ll lsf sge pbs cobalt<br> Checkpointing libraries available: <br> Demux engines available: poll select<br><br></font>
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