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A lock statement, in C#, is a statement that contains the "lock" keyword and is used in multithreaded applications to ensure that the current thread executes a block of code to completion without interruption by other threads. The lock statement obtains a mutual exclusion lock for a given object so that one thread executes the code block at a time and exits the code block after releasing the lock.
The lock statement is an exclusive locking construct used to ensure synchronized access to shared data in multithreaded applications. It helps to protect the integrity of a mutable resource that is shared by multiple threads without creating interference between those threads. The lock statement can be used by a singleton object to prevent concurrent access of its common data by multiple clients.
The lock statement is the primary synchronization primitive available in the .NET Framework Class Library. It automatically generates consistent and exception-safe code that can handle synchronization needs in multithreaded programs. It also provides an easy method to control synchronization by generating efficient code, which prevents errors that can be caused by manually written code.
The lock statement should be provided with an argument of reference type, not of value type. In general, it is recommended to lock on a private instance member or private static member to protect the data that is shared among all the instances of the object. Since locking on public type or instances that are beyond the control of code can result in deadlock situations where multiple threads wait for the release of a single object used for a lock statement, they have to be avoided.
An example for the usage of the lock statement can be a multithreaded application in which an account object with a method to withdraw a balance uses the lock statement to prevent multiple threads from executing the same method simultaneously, which could push the balance to a negative number.
The body of a lock statement needs to be small to reduce the time needed for other threads waiting on the lock, decreasing the chances for deadlock and minimizing the possibility that an exception will occur.
The limitations in using lock statements include that they can only be used with data that's relevant to the current application. Lock statements are also unable to support a timeout.