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#############################################################################
##
#W cache.gi GAP library Chris Jefferson
##
##
#Y Copyright (C) 2017 University of St Andrews, Scotland
##
## This file defines various types of caching data structures
##
## Note that this file is read very early in GAP's startup, so we cannot
## make MemoizePosIntFunction a method and use method dispatch, or other
## bits of nice GAP functionality.
##
InstallGlobalFunction(MemoizePosIntFunction,
function(func, extra...)
local boundvals, original, uniqueobj, options, r;
# This is an object which cannot exist anywhere else
uniqueobj := "";
options := rec(
defaults := [],
flush := true,
errorHandler := function(x)
ErrorNoReturn("<val> must be a positive integer");
end);
if LEN_LIST(extra) > 0 then
for r in REC_NAMES(extra[1]) do
if IsBound(options.(r)) then
options.(r) := extra[1].(r);
else
ErrorNoReturn("Invalid option: ", r);
fi;
od;
fi;
original := AtomicList(options.defaults);
boundvals := MakeWriteOnceAtomic(AtomicList(original));
if options.flush then
InstallMethod(FlushCaches, [],
function()
boundvals := MakeWriteOnceAtomic(AtomicList(original));
TryNextMethod();
end);
fi;
return function(val)
local v, boundcpy;
if not IsPosInt(val) then
return options.errorHandler(val);
fi;
# Make a copy of the reference to boundvals, in case the cache
# is flushed, which will causes boundvals to be bound to a new list.
boundcpy := boundvals;
v := GetWithDefault(boundcpy, val, uniqueobj);
if IsIdenticalObj(v, uniqueobj) then
# As the list is WriteOnceAtomic, if two threads call
# func(val) at the same time they will still return the
# same value (the first assigned to the list).
boundcpy[val] := func(val);
v := boundcpy[val];
fi;
return v;
end;
end);
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