Title: COMP309/509 - Lecture 16 class: middle, center, inverse

COMP309/509 - Parallel and Distributed Computing

Lecture 16 - PVM Progamming Examples

By Mitchell Welch

University of New England

Reading

• The PVM User Interface from PVM: Parallel Virtual Machine A Users' Guide and Tutorial for Networked Parallel Computing

Summary

• Makefiles in PVM
• Error Checking PVM Function Calls
• PVM Examples Walk-through

Makefiles in PVM

• makefiles are required in all assignments.
• Your make file should contain:
  • An all target so produce all executables for the assignment
  • A clean target that will allow for fast rebuilds (i.e. it should remove all binaries from the build directory)
  • For PVM programs it should contain a host target to copy all required executables to the pvm/bin/LINUXX86_64 directory.

Makefiles in PVM

• Sample makefile:

COMPILER = gcc
CFLAGS =  -Wall
LIBS = -L$(PVM_ROOT)/lib/$(PVM_ARCH) -I$(PVM_ROOT)/include -lpvm3
GLIBS = ${LIBS} -lgpvm3 
EXES = spmd2

all:   ${EXES}

spmd2: spmd2.c
    ${COMPILER} ${CFLAGS} spmd2.c $(GLIBS) -o spmd2  

host:
    cp -f ${EXES} ${HOME}/pvm3/bin/$(PVM_ARCH)/  

clean: 
    rm -f *~ *.o  ${EXES}

Makefiles in PVM

• This is the makefile for the example in lecture 15
• Notice the environment variables PVM_ROOT and PVM_ARCH
• These must set when you install PVM so that they available for PVM itself and also for use by make.
• Note the library and include paths in the LIBS variable. These should remain the same for your makefiles.

Error Checking PVM Function Calls

• All(?) PVM routines return negative error codes.
• More accurately: If a PVM routine returns a negative number, it indicates an error.
• On success, most but not all, return the constant PvmOk
• PvmOk is zero.
• Some, like pvm_spawn, return a non-negative number on success.
• A good professional programmer would check each PVM library call!
• If not done systematically this can lead to code bloat, and errors.

Error Checking PVM Function Calls

• One idea is to have a routine:

int pvm_error_check(int info, char* routine){
  if(info < 0){
    fprintf(stderr, 
            "PVM error code %d: %s failed -- aborting\n", 
            info, routine);
    pvm_exit();
    exit(EXIT_FAILURE);
  } 
  return info;
}

Error Checking PVM Function Calls

• Then instead of:

int receive_row(int tid, int nproc, int* row){
  pvm_recv(tid, ROWTAG);
  return pvm_upkint(row, nproc, 1);  
}

• Write:

int receive_row(int tid, int nproc, int* row){
  pvm_error_check(pvm_recv(tid, ROWTAG), "receive_row:pvm_recv");
  return pvm_error_check(pvm_upkint(row, nproc, 1), "receive_row:pvm_upkint");  
}

Error Checking PVM Function Calls

• Though this has the following disadvantages:
  • The call to pvm_exit(); exit(EXIT_FAILURE); is hardwired in.
  • The call to exit(EXIT_FAILURE); is thus hidden at top level.
• Another possibility is to use a macro

#define  PVM_ERROR_CHECK(X, Y) \
{ int _err_rtn_;\
  if((_err_rtn_ = X) < 0){\
    fprintf(stderr, "PVM error code %d: %s failed -- aborting\n", _err_rtn_, #X);\
    (Y);  } }

• For an example of using this see e_macro.c

Error Checking PVM Function Calls

• PVM has (at least) 27 error codes.
• All are negative integers.
• A good professional programmer who had to write PVM programs routinely would improve on the previous version of pvm_error_check like so:

Error Checking PVM Function Calls

int pvm_error_check(int info, char* routine){
  if(info < 0){
    fprintf(stderr, 
            "PVM error %s: %s failed -- aborting\n", 
            pvmErrorCode2String(info), routine);
    pvm_exit();
    exit(EXIT_FAILURE);
  } 
  return info;
}
char* pvmErrorCode2String(int errcode){
  switch(errcode){
  case PvmBadParam:   return "PvmBadParam";
  case PvmMismatch:   return "PvmMismatch";
  case PvmNoData:     return "PvmNoData";
  case PvmNoHost:     return "PvmNoHost";
  case PvmNoFile:     return "PvmNoFile";
  case PvmNoMem:      return "PvmNoMem";
  case PvmBadMsg:     return "PvmBadMsg";
  case PvmSysErr:     return "PvmSysErr";
  case PvmNoBuf:      return "PvmNoBuf";
  case PvmNoSuchBuf:  return "PvmNoSuchBuf";
  case PvmNullGroup:  return "PvmNullGroup";
  case PvmDupGroup:   return "PvmDupGroup";
  case PvmNoGroup:    return "PvmNoGroup";
  case PvmNotInGroup: return "PvmNotInGroup";
  case PvmNoInst:     return "PvmNoInst";
  case PvmHostFail:   return "PvmHostFail";
  case PvmNoParent:   return "PvmNoParent";
  case PvmNotImpl:    return "PvmNotImpl";
  case PvmDSysErr:    return "PvmDSysErr";
  case PvmBadVersion: return "PvmBadVersion";
  case PvmOutOfRes:   return "PvmOutOfRes";
  case PvmDupHost:    return "PvmDupHost";
  case PvmCantStart:  return "PvmCantStart";
  case PvmAlready:    return "PvmAlready";
  case PvmNoTask:     return "PvmNoTask";
  case PvmNoEntry:    return "PvmNoEntry";
  case PvmDupEntry:   return "PvmDupEntry";
  default:            return "Unknown Code";
  }
}

PVM Examples Walk-through

• Last lecture we looked at synchronization and dynamic groups in PVM.
• In particular we saw how to build a token ring using groups.
• In this lecture we’ll look at how to build rings without dynamic groups.
• Recall that the main use of dynamic groups was to ascertain ones rank in the ring.
• As well as the tids of thine neighbours!

PVM Examples Walk-through

• We have already seen how to do this without dynamic groups:
• The parent broadcasts the array of tids to the slaves!
• Each slave finds its tid in the array and uses that index as its rank.
• The neighbouring tids are it’s neighbours of course!

PVM Examples Walk-through

• sspmd.c - no error checking
• e_sspmd.c - with our error checking function
• vsspmd.c - variable sized ring
• e_vsspmd.c - variable sized ring with error checking
  • Examples Directory

Summary

• Makefiles in PVM
• Error Checking PVM Function Calls
• PVM Example Walkthrough

class: middle, center, inverse

Questions?

Reading

• The PVM User Interface from PVM: Parallel Virtual Machine A Users' Guide and Tutorial for Networked Parallel Computing