Unsafe: removing the monitorEnter/monitorExit/tryMonitorEnter methods

[David Holmes]

On 5/03/2014 1:32 AM, David M. Lloyd wrote:
> On 03/03/2014 09:45 PM, David Holmes wrote:
>> On 3/03/2014 10:56 PM, David M. Lloyd wrote:
>>> Yes, that would necessarily be the contract of a Monitors class, just as
>>> it is part of the contract of Lock today.  If your argument is that it
>>> shouldn't be allowed because it might be used wrong, we might as well
>>> just delete most of the JDK, ReentrantLock included, since it suffers
>>> from the exact same potential problem.  The difference is that monitors
>>> have a simple API in the form of synchronized that people were in the
>>> past and would continue to be free (and recommended) to use.
>>
>> We should not introduce anything that allows something that was
>> guaranteed to be safe by the language, to become unsafe.
>
> Define 'safe'.  Because I don't think it's unsafe, any more than
> unpaired lock/unlock are.  There is no uninitialized memory being
> accessed, no way to bypass security checks, no way to manipulate memory
> directly, etc.  I find this argument to be particularly weak without
> specific cases.  As far as I can tell, the language doesn't make it
> safe, it makes it *convenient*, and that's a big distinction.

I agree it is as unsafe as using Lock. I think not being able to forget 
to unlock a monitor is more than just convenient. YMMV and obviously does.

David
-----

> There are two cases I can see that are potentially problematic: extra
> acquires, and extra releases.
>
> The risk of extra acquires is that the thread might exit while still
> holding the lock, leaving it locked forever.  However, just parking a
> thread indefinitely (via various means) within a synchronized block is
> equally unsafe.
>
> The risk of extra releases is that you'll hit IllegalMonitorState
> exceptions and thread-safety/publication problems.  But a user can make
> this same mistake today with locks.  The difference is, that in most
> cases people would choose the convenience of synchronized unless there
> is a specific reason for it, making this problem far less likely than
> the corresponding locks case.
>