c# - LINQ on loop conditions -

let's suppose have following piece of code:

ienumerable<string> allkeys = _cache.select(o => o.key); parallel.foreach(allkeys, key => _cache.remove(key)); 

as can see, i'm retrieving keys in _cache, storing them in local variable allkeys, , concurrently removing keys _cache.

i however, 1 single line. comes mind is:

parallel.foreach(_cache.select(o => o.key), key => _cache.remove(key)); 

but statement _cache.select(o => o.key) called on each loop iteration, therefore retrieving different amount of elements each time (because i'm deleting them @ same time).

is latter line of code safe?

does _cache.select(o => o.key) in loop statements, called once, , each iteration uses original result, or processed in every iteration step?

as can see, i'm retrieving keys in _cache, storing them in local variable allkeys

no, don't. due called deferred execution, store command keys. need materialize command think do:

var allkeys = _cache.select(o => o.key).tolist();

that said: cache thread safe? why not feature clear method? getting keys , removing using multi threading seems not-so-great-idea.

if insist have in 1 line, use plinq:

_cache.select(o => o.key).asparallel().forall(key => _cache.remove(key)); 

but again: seems bad idea.