PGAS Programming with UPC and Fortran Coarrays
PGAS Programming with UPC and Fortran Coarrays
PGAS Programming with UPC and Fortran Coarrays
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segmentsegment12/19/2012More on Synchronisation• We have to be careful <strong>with</strong> one-sided updates• If we read remote data, was it valid?• Could another process send us data <strong>and</strong> overwritesomething we have not yet used?• How do we know when remote data has arrived?• The st<strong>and</strong>ard introduces execution segments to deal <strong>with</strong> this:segments are bounded by image control statementsThe st<strong>and</strong>ard can be summarized as follows:• If a variable is defined in a segment, it must not be referenced,defined, or become undefined in another segment unless thesegments are ordered – John Reid3Execution Segmentsimage 1program hotdouble precision :: a(n)double precision :: temp(n)[*]!...if (this_image() == 1) thendo i=1, num_images()read *,atemp(:)[i] = aend doend iftemp = temp + 273d0sync all! …call ensemble(temp)2image 2program hotdouble precision :: a(n)double precision :: temp(n)[*]!...if (this_image() == 1) thendo i=1, num_images()read *,atemp(:)[i] = aend doend if2temp = temp + 273d0sync all! …call ensemble(temp)orderingiimage synchronisation points42
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