10.10 Execution order

10.10 Execution order

Execution shall proceed such that the side effects of each executing thread

are preserved at critical execution

points. A side effect is defined as a read or write of a volatile field, a

write to a non-volatile variable, a write

to an external resource, and the throwing of an exception. The critical

execution points at which the order of

these side effects must be preserved are references to volatile fields (?7.4

.3), lock statements (?5.12), and

thread creation and termination. An implementation is free to change the

order of execution of a

C# program, subject to the following constraints:

?Data dependence is preserved within a thread of execution. That is, the

value of each variable is

computed as if all statements in the thread were executed in original

program order.

?Initialization ordering rules are preserved (?7.4.4 and ?7.4.5).

?The ordering of side effects is preserved with respect to volatile reads

and writes (?7.4.3). Additionally,

an implementation need not evaluate part of an expression if it can deduce

that that expression.s value is

not used and that no needed side effects are produced (including any caused

by calling a method or

accessing a volatile field). When program execution is interrupted by an

asynchronous event (such as an

exception thrown by another thread), it is not guaranteed that the

observable side effects are visible in

the original program order.