All--
I'm having a problem with the ReadWriteLock object in .net and wondering
if I'm misunderstanding the concept:
The class I've written manages a log that stores messages in a queue and
periodically flushes the queue to save the messages to a text file.
In order to minimize blocking, I've written the class to copy the queue
into an array, reset the queue, and release the reader lock. There is no
place anywhere else that the queue is reinitialized or anything is
dequeued.
And yet, I am still having a problem where, during amsg = mQueue.ToArray
is failing because the queue is empty. FileSave is never called with the
queue empty.
I suspect there's some conceptual error here, but I'll be damned if I
can figure it out on my own. Can anyone help?
TIA
--Jekke
Protected Sub FileSave()
'Lock all threads out of the queue while we copy it.
mWRLQueue.AcquireReaderLock(miQueueReadWriteTimeout)
'Copy the message queue to an array.
Dim amsg() As Object
If mQueue.Count > 0 Then
amsg = mQueue.ToArray()
'Clear the queue
mQueue = New LogMessageQueue
Else
mWRLQueue.ReleaseReaderLock()
Exit Sub
End If
mWRLQueue.ReleaseReaderLock()
'The queue is not touched after this point. Nothing to see below
here...probably
'Saving the file is a critical section. Disc read/write must
'be done by exactly one thread at a time.
SyncLock FileSLMessage
'Open or create the logfile
Dim sr As StreamWriter = File.AppendText(msFileName)
'Write each message to the end of the logfile.
Dim thisObj As Object
Dim thisMsg As LogMessage
For Each thisObj In amsg
thisMsg = CType(thisObj, LogMessage)
'Only write messages that reach the required level
'of severity. This way, developers can change
SeverityTolerance
'on later builds to get less verbose information.
If thisMsg.Severity >= miSeverityTolerance Then
sr.WriteLine(thisMsg.ToString())
End If
Next
'Save and close the file.
sr.Flush()
sr.Close()
End SyncLock
End Sub
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