Syncing file-backed variables.
Actions to propagate changes to file-backed Rdsm variables across a shared file system.
Name of the Rdsm variable, quoted.
This feature should be considered experimental, with poor performance and portability.
Suppose we have an Rdsm variable
x which is in
backing store (
fs = TRUE in call to
that we on a shared file system. (These functions are not needed if all
threads are on the same machine.) When one Rdsm thread writes to
x, the question here is when the updated value for
visible to other Rdsm threads.
The answer may depend on the underlying file system. The functions
writesync() force the updates across the
network. Normally one would call
rdsmlock() and call
writesync() just before calling
These should work on systems with "close-to-open cache coherency," as with the Network File System (NFS). On some systems, these functions should be unnecessary.
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library(parallel) c2 <- makeCluster(2) mgrinit(c2) mgrmakevar(c2,"x",1,1,fs=TRUE) clusterEvalQ(c2,me <- myinfo$id) clusterEvalQ(c2,if (me==1) x[1,1] <- 3) # force update on network clusterEvalQ(c2,if (me==1) writesync("x")) clusterEvalQ(c2,if (me==2) readsync("x")) clusterEvalQ(c2,if (me==2) x[1,1]) # should be 3 clusterEvalQ(c2,if (me==2) x[1,1] <- 8) clusterEvalQ(c2,if (me==2) writesync("x")) clusterEvalQ(c2,if (me==1) readsync("x")) clusterEvalQ(c2,x[1,1]) # both should yield 8
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