Question

I’m trying to use a mutex to protect access to some hardware from multiple threads, but I’m confused as to what the exitContext parameter means / does:

public virtual bool WaitOne (
    int millisecondsTimeout,
    bool exitContext
)

The docs say:

exitContext – true to exit the synchronization domain for the context before the wait (if in a synchronized context), and reacquire it afterward; otherwise, false.

…but what does that actually mean and what are the consequences of setting it to either true or false? I’ve set it to true for now and the code appears to work, but I’m nervous that I don’t fully understand what it’s up to under the hood!

Answer 1

It also explains further down the page under Remarks that:

Notes on Exiting the Context

The exitContext parameter has no effect unless the WaitOne method is
called from inside a nondefault managed context. This can happen if
your thread is inside a call to an instance of a class derived from
ContextBoundObject. Even if you are currently executing a method on a
class that does not derive from ContextBoundObject, like String, you
can be in a nondefault context if a ContextBoundObject is on your
stack in the current application domain.

When your code is executing in a nondefault context, specifying true
for exitContext causes the thread to exit the nondefault managed
context (that is, to transition to the default context) before
executing the WaitOne method. The thread returns to the original
nondefault context after the call to the WaitOne method completes.

This can be useful when the context-bound class has
SynchronizationAttribute. In that case, all calls to members of the
class are automatically synchronized, and the synchronization domain
is the entire body of code for the class. If code in the call stack of
a member calls the WaitOne method and specifies true for exitContext,
the thread exits the synchronization domain, allowing a thread that is
blocked on a call to any member of the object to proceed. When the
WaitOne method returns, the thread that made the call must wait to
reenter the synchronization domain.