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avoid segmentation faults in universe/uloop variable increment

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This commit is contained in:
Axel Kohlmeyer
2020-03-25 08:19:24 -04:00
parent 398c030925
commit 1192845ad5
1 changed files with 29 additions and 4 deletions
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33
src/variable.cpp
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@ -661,6 +661,8 @@ int Variable::next(int narg, char **arg)
} else if (istyle == UNIVERSE || istyle == ULOOP) { } else if (istyle == UNIVERSE || istyle == ULOOP) {
uloop_again:
// wait until lock file can be created and owned by proc 0 of this world // wait until lock file can be created and owned by proc 0 of this world
// rename() is not atomic in practice, but no known simple fix // rename() is not atomic in practice, but no known simple fix
// means multiple procs can read/write file at the same time (bad!) // means multiple procs can read/write file at the same time (bad!)
@ -669,7 +671,7 @@ int Variable::next(int narg, char **arg)
// delay for random fraction of 1 second before subsequent tries // delay for random fraction of 1 second before subsequent tries
// when successful, read next available index and Bcast it within my world // when successful, read next available index and Bcast it within my world
int nextindex; int nextindex = -1;
if (me == 0) { if (me == 0) {
int seed = 12345 + universe->me + which[find(arg[0])]; int seed = 12345 + universe->me + which[find(arg[0])];
RanMars *random = new RanMars(lmp,seed); RanMars *random = new RanMars(lmp,seed);
@ -682,10 +684,33 @@ int Variable::next(int narg, char **arg)
} }
delete random; delete random;
FILE *fp = fopen("tmp.lammps.variable.lock","r"); // if the file cannot be found, we may have a race with some
fscanf(fp,"%d",&nextindex); // other MPI rank that has called rename at the same time
//printf("READ %d %d\n",universe->me,nextindex); // and we have to start over.
// if the read is short (we need at least one byte) we try reading again.
FILE *fp;
char buf[64];
for (int loopmax = 0; loopmax < 100; ++loopmax) {
fp = fopen("tmp.lammps.variable.lock","r");
if (fp == NULL) goto uloop_again;
buf[0] = buf[1] = '\0';
fread(buf,1,64,fp);
fclose(fp); fclose(fp);
if (strlen(buf) > 0) {
nextindex = atoi(buf);
break;
}
delay = (int) (1000000*random->uniform());
usleep(delay);
}
if (nextindex < 0)
error->one(FLERR,"Unexpected error while incrementing uloop "
"style variable. Please contact LAMMPS developers.");
//printf("READ %d %d\n",universe->me,nextindex);
fp = fopen("tmp.lammps.variable.lock","w"); fp = fopen("tmp.lammps.variable.lock","w");
fprintf(fp,"%d\n",nextindex+1); fprintf(fp,"%d\n",nextindex+1);
//printf("WRITE %d %d\n",universe->me,nextindex+1); //printf("WRITE %d %d\n",universe->me,nextindex+1);