David, Vitaly, I totally agree with Vitaly's explanation (Vitaly - thank you for that) and code in shmemBase.c (the usage of enterMutex() function for sending/receiving bytes through shared memory connection) illustrates on how the connection shutdown event is used as a "cancellation token". Thank you, -Aleksej On 05/14/2014 01:05 PM, David Holmes wrote:
On 14/05/2014 11:06 AM, Vitaly Davidovich wrote:
In windows, you acquire a mutex by waiting on it using one of the wait functions, one of them employed in the code in question. If WaitForMultipleObjects succeeds and returns the index of the mutex, current thread has ownership now.
Yes I understand the basic mechanics :)
It's also common to use multi wait functions where the event is a "cancelation token", e.g. manual reset event; this allows someone to cancel waiting on mutex acquisition and return from the wait function. Presumably that's the case here, but I'll let Aleksej confirm; just wanted to throw this out there in the meantime :).
Ah I see - yes cancellable lock acquisition would make sense.
Thanks, David
Sent from my phone
On May 13, 2014 6:46 PM, "David Holmes" <david.holmes@oracle.com <mailto:david.holmes@oracle.com>> wrote:
Hi Aleksej,
Thanks for the doc references regarding abandonment.
Let me rephrase my question. What is this logic trying to achieve by waiting on both a mutex and an event? Do we already own the mutex when this function is called?
David
On 13/05/2014 11:19 PM, Aleksej Efimov wrote:
David,
The Windows has a different terminology for mutex objects (much differs from the POSIX one). This one link gave me some understanding of it [1].
Here is the MSDN [1] description of what "abandoned mutex" is: " If a thread terminates without releasing its ownership of a mutex object, the mutex object is considered to be abandoned. A waiting thread can acquire ownership of an abandoned mutex object, but the wait function will return*WAIT_ABANDONED*to indicate that the mutex object is abandoned. An abandoned mutex object indicates that an error has occurred and that any shared resource being protected by the mutex object is in an undefined state. If the thread proceeds as though the mutex object had not been abandoned, it is no longer considered abandoned after the thread releases its ownership. This restores normal behavior if a handle to the mutex object is subsequently specified in a wait function."
What does it mean to wait on mutex and ownership of the mutex object: "Any thread with a handle to a mutex object can use one of thewait functions <http://msdn.microsoft.com/en-__gb/library/windows/desktop/__ms687069%28v=vs.... <http://msdn.microsoft.com/en-gb/library/windows/desktop/ms687069%28v=vs.85%29.aspx>>to request ownership of the mutex object. If the mutex object is owned by another thread, the wait function blocks the requesting thread until the owning thread releases the mutex object using the*ReleaseMutex* <http://msdn.microsoft.com/en-__gb/library/windows/desktop/__ms685066%28v=vs.... <http://msdn.microsoft.com/en-gb/library/windows/desktop/ms685066%28v=vs.85%29.aspx>>__function."
How we can release mutex and wait on already owned mutex: " After a thread obtains ownership of a mutex, it can specify the same mutex in repeated calls to the wait-functions <http://msdn.microsoft.com/en-__gb/library/windows/desktop/__ms687069%28v=vs.... <http://msdn.microsoft.com/en-gb/library/windows/desktop/ms687069%28v=vs.85%29.aspx>>__without blocking its execution. This prevents a thread from deadlocking itself while waiting for a mutex that it already owns. To release its ownership under such circumstances, the thread must call*ReleaseMutex* <http://msdn.microsoft.com/en-__gb/library/windows/desktop/__ms685066%28v=vs.... <http://msdn.microsoft.com/en-gb/library/windows/desktop/ms685066%28v=vs.85%29.aspx>>__once for each time that the mutex satisfied the conditions of a wait function."
[1] http://msdn.microsoft.com/en-__gb/library/windows/desktop/__ms684266(v=vs.85... <http://msdn.microsoft.com/en-gb/library/windows/desktop/ms684266(v=vs.85).aspx>
-Aleksej
On 05/13/2014 04:00 PM, David Holmes wrote:
I don't understand this one at all. What is an "abandoned mutex"? For that matter why does the code wait on a mutex and an event? Do we already own the mutex? If so what does it mean to wait on it? If not then how can we release it?
???
Thanks, David
On 13/05/2014 8:57 PM, Alan Bateman wrote:
This is debugger's shared memory transport so cc'ing serviceability-dev as that is there this code is maintained.
Is there a test case or any outline of the conditions that cause this? I think that would be useful to understand the issue further.
-Alan
On 13/05/2014 11:46, Aleksej Efimov wrote:
Hi,
Can I have a review for 8032901 bug [1] fix [2]. There is a possible case when 'WaitForMultipleObjects' function can return the WAIT_ABANDONED_0 [3] error value. In such case it's better to release the mutex and return error value. This will prevent other threads to be blocked on abandoned mutex.
Thank you, Aleksej
[1] https://bugs.openjdk.java.net/__browse/JDK-8032901 <https://bugs.openjdk.java.net/browse/JDK-8032901> [2] http://cr.openjdk.java.net/~__aefimov/8032901/9/webrev.00/ <http://cr.openjdk.java.net/~aefimov/8032901/9/webrev.00/> [3] http://msdn.microsoft.com/en-__gb/library/windows/desktop/__ms687025(v=vs.85... <http://msdn.microsoft.com/en-gb/library/windows/desktop/ms687025(v=vs.85).aspx>