mscorlib 4.0.0.0 System.Enum

Use this enumeration to specify the parameter of constructors. The effects of all constructors on thread synchronization can be described in terms of this enumeration, whether or not they have parameters.

A instance is initialized either by a user-specified initialization method or by the default constructor for . The initialization method is specified by the parameter of a constructor. The method returns an instance of , which is the type that is lazily instantiated by the instance of . If a constructor does not have a parameter, the default constructor for is used to initialize the instance. In either case, initialization occurs the first time you call the property.

In addition to specifying the thread safety of a instance, this enumeration affects exception caching. When exceptions are cached for a instance, you get only one chance to initialize the instance. If an exception is thrown the first time you call the property, that exception is cached and rethrown on all subsequent calls to the property. The advantage of caching exceptions is that any two threads always get the same result, even when errors occur.

When you specify the mode, exceptions are never cached. When you specify or , caching depends on whether you specify an initialization method or allow the default constructor for to be used. Specifying an initialization method enables exception caching for these two modes. The initialization method can be very simple. For example, it might call the default constructor for : new Lazy<Contents>(() => new Contents(), mode) in C#, or New Lazy(Of Contents)(Function() New Contents()) in Visual Basic. If you use a constructor that does not specify an initialization method, exceptions that are thrown by the default constructor for are not cached. The following table summarizes exception caching behavior.

Mode

Using initialization method

Using default constructor for

Cached

Not cached

Not cached

Not cached

Cached

Not cached

Specifies how a instance synchronizes access among multiple threads.

- Field
  4.0.0.0
  System.Threading.LazyThreadSafetyMode

  Locks are used to ensure that only a single thread can initialize a instance in a thread-safe manner. If the initialization method (or the default constructor, if there is no initialization method) uses locks internally, deadlocks can occur. If you use a constructor that specifies an initialization method ( parameter), and if that initialization method throws an exception (or fails to handle an exception) the first time you call the property, then the exception is cached and thrown again on subsequent calls to the property. If you use a constructor that does not specify an initialization method, exceptions that are thrown by the default constructor for are not cached. In that case, a subsequent call to the property might successfully initialize the instance. If the initialization method recursively accesses the property of the instance, an is thrown.

- Field
  4.0.0.0
  System.Threading.LazyThreadSafetyMode

  The instance is not thread safe; if the instance is accessed from multiple threads, its behavior is undefined. Use this mode only when high performance is crucial and the instance is guaranteed never to be initialized from more than one thread. If you use a constructor that specifies an initialization method ( parameter), and if that initialization method throws an exception (or fails to handle an exception) the first time you call the property, then the exception is cached and thrown again on subsequent calls to the property. If you use a constructor that does not specify an initialization method, exceptions that are thrown by the default constructor for are not cached. In that case, a subsequent call to the property might successfully initialize the instance. If the initialization method recursively accesses the property of the instance, an is thrown.

- Field
  4.0.0.0
  System.Threading.LazyThreadSafetyMode

  When multiple threads try to initialize a instance simultaneously, all threads are allowed to run the initialization method (or the default constructor, if there is no initialization method). The first thread to complete initialization sets the value of the instance. That value is returned to any other threads that were simultaneously running the initialization method, unless the initialization method throws exceptions on those threads. Any instances of that were created by the competing threads are discarded. If the initialization method throws an exception on any thread, the exception is propagated out of the property on that thread. The exception is not cached. The value of the property remains false, and subsequent calls to the property, either by the thread where the exception was thrown or by other threads, cause the initialization method to run again. If the initialization method recursively accesses the property of the instance, no exception is thrown.