volatile (C# Reference) （转自msdn）

The volatile keyword indicates that a field might be modified by multiple threads that are executing at the same time. Fields that are declared volatile are not subject to compiler optimizations that assume access by a single thread. This ensures that the most up-to-date value is present in the field at all times.

The volatile modifier is usually used for a field that is accessed by multiple threads without using the lock statement to serialize access.

The volatile keyword can be applied to fields of these types:

• Reference types.

• Pointer types (in an unsafe context). Note that although the pointer itself can be volatile, the object that it points to cannot. In other words, you cannot declare a "pointer to volatile."

• Types such as sbyte, byte, short, ushort, int, uint, char, float, and bool.

• An enum type with one of the following base types: byte, sbyte, short, ushort, int, or uint.

• Generic type parameters known to be reference types.

• IntPtr and UIntPtr.

The volatile keyword can only be applied to fields of a class or struct. Local variables cannot be declared volatile.