Lock statements

A lock statement executes a body while holding the monitor associated with a reference value:

lock gate {
    updateSharedState()
}

The lock expression must have a reference type. It is evaluated exactly once before the monitor is acquired. The monitor is released when control leaves the body, including when the body returns or throws an exception.

The statement is equivalent in effect to evaluating the expression into a hidden local, calling System.Threading.Monitor.Enter, executing the body in a try, and calling System.Threading.Monitor.Exit from finally.