Hi;

I have a hashtable that I am using in my codebehind in ASP.NET. In that
codebehind the hashtable is read, written to, and enumerated. Each entry in
the hashtable is tied to a session - the SessionId is the key for the entry.
So I will only have 1 thread writing to or reading from a specific entry in
the hashtable.

But there can be multiple threads (sessions) that all read/write/add/remove
the table at the same time. Reading the docs it looks like I need to put all
this access inside a lock() {...} or is there a better way?

--
thanks - dave
david_at_windward_dot_net
http://www.windwardreports.com

Cubicle Wars - http://www.windwardreports.com/film.htm

Using a lock is really the answer. So long as you need to
read/write/enumerate from any number of threads, you're stuck doing that.

In some use cases, the ReaderWriterLock works out better - it depends on the
ration of reads to the writes.

--
Chris Mullins, MCSD.NET, MCPD:Enterprise
http://www.coversant.net/blogs/cmullins

[quoted text, click to view]

Hi Dave,

Yes, from the doc we will know that when multiple threads may read/write to
the HashTable in the same time, we need to do thread synchronization.

Thread Safety
Hashtable is thread safe for use by multiple reader threads, or a single
writing thread. It is not thread safe for multi-thread use, when any of the
threads perform write (update) operations. To support multiple writers all
operations on the Hashtable must be done through the wrapper returned by
the Synchronized method, provided that there are no threads reading the
Hashtable object.

Enumerating through a collection is intrinsically not a thread safe
procedure. Even when a collection is synchronized, other threads can still
modify the collection, which causes the enumerator to throw an exception.
To guarantee thread safety during enumeration, you can either lock the
collection during the entire enumeration or catch the exceptions resulting
from changes made by other threads.
Hashtable Class
http://msdn2.microsoft.com/en-us/library/system.collections.hashtable.aspx

Hashtable.Synchronized Method
http://msdn2.microsoft.com/en-us/library/system.collections.hashtable.synchr
onized.aspx

In addition to the lock method, we have other approach thread
synchronization approach, but I think this one is easier.
e.g. ReaderWriterLock, AutoResetEvent and so on.

The goal to do thread synchronization is to prevent the scenario that
multiple threads access to a not thread safe object in the same time. In
this scenario, no writer thread and read thread access to the HashTable in
the same time.

Best regards,

Perter Huang
Microsoft Online Partner Support

Get Secure! - www.microsoft.com/security
This posting is provided "AS IS" with no warranties, and confers no rights.

Yep, doing all that. However the reads have to be in a lock also as the
add/delete could be happening during the read.

--
thanks - dave
david_at_windward_dot_net
http://www.windwardreports.com

Cubicle Wars - http://www.windwardreports.com/film.htm




[quoted text, click to view]