c# - Parallel.Foreach vs Foreach and Task in local variable -

when use foreach , tasks need use local variables this:

list<task> taskpool = new list<task>(); foreach (targettype item in source) {   targettype localitem = item;   taskpool.add(task.factory.startnew(() => dosomething(localitem))); } task.waitall(taskpool.toarray()); 

but how parallel.foreach, use this:

parallel.foreach(source, (targettype item) => dosomething(item)); 

so there not local variable see. how parallel.foreach work? there no need introduce local variables? or if needed, how can define it?

update

is there difference in .net 4 , .net 4.5?

you not define local variable in parallel.foreach - item nothing more formal parameter - implementation code of parallel.foreach 1 have handle variables, , whether local, captured or else.

there no need define local variable related formal parameter parallel.foreach - caller code of anonymous delegate handle variable , pass function.

however in c#4, might need use local variable if capture variable, is:

void dosomething(itemtype item, othertype other) { }  void yourfunction(ienumerable<itemtype> items, ienumerable<othertype> others) {      foreach (var otheritem in others) {         var localotheritem = otheritem;         parallel.foreach(items, item => dosomething(item, localotheritem));     } } 

you can see difference above: localotheritem taken context anonymous function defined: called closure. whereas items in items passed method parameter anonymous function.

in short: item in parallel.foreach , item in c# foreach 2 different problems.