volatile keyword

• The volatile keyword indicates that a field can be modified in the program by something such as the operating system, the hardware, or a concurrently executing thread.
• The system always reads the current value of a volatile object at the point it is requested, even if the previous instruction asked for a value from the same object. Also, the value of the object is written immediately on assignment.
• The volatile modifier is usually used for a field that is accessed by multiple threads without using the lock statement to serialize access. Using the volatile modifier ensures that one thread retrieves the most up-to-date value written by another thread.
• The type of a field marked as volatile is restricted to the following types:
  * Any reference type.
  * Any pointer type (in an unsafe context).
  * The types sbyte, byte, short, ushort, int, uint, char, float, bool.
  * An enum type with an enum base type of byte, sbyte, short, ushort, int, or uint.

C# Programmer's Reference - volatile