Re: How to use lock in C# - C# Discussion Boards

24-Mar-06 1:17

I have written a multithread program using lock(this) to realize sync.
I hung up the other day and i was told lock(this) is not a good way.
Can anyone give me some advice and tell my why?

Thank you!

leppie24-Mar-06 1:40

leppie

24-Mar-06 1:40

Bob_Sun wrote:
i was told lock(this) is not a good way.

And why didnt he back up his claim? It all depends what you need lock'd, but more important where the locking takes place.

xacc.ide-0.1.3.2

Bob_Sun24-Mar-06 4:54

24-Mar-06 4:54

I was just told that lock(this) is a bad sample which will bring about unlocked problem but no further back up. I found the following forum instead. And I am a little bit puzzled.

http://msdn.microsoft.com/msdnmag/issues/03/01/NET/[^]

Guffa24-Mar-06 1:44

24-Mar-06 1:44

What was wrong with the question you posted only half an hour before? Don't spam the forum.

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Bob_Sun24-Mar-06 4:48

24-Mar-06 4:48

Soory for made a mistake to post 2 messages.

I think it is better to use this thread only

Guffa24-Mar-06 4:57

24-Mar-06 4:57

Bob_Sun wrote:
I think it is better to use this thread only

I already replied in the first thread.

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Bob_Sun24-Mar-06 5:39

24-Mar-06 5:39

Thank you very much.
I have read your following reply.

Who told you that it wasn't a good way, and what was the arguments for that?

I was just told so, and I found the following forum.
http://msdn.microsoft.com/msdnmag/issues/03/01/NET/[^]

Locking should of course be kept as a minimum, and to avoid deadlocks a thread should never lock more than one object at a time. Still, for sharing data between threads there is hardly any alternative.

I wrote a class for statemachine, whenever a event is dispatched, the whole statemachine should be locked in the thread. As for number of objects locked in this thread, it is always more than 2. As this is a statemachine, state changes must be sent to upper class. As the so called upper class collects messages from many child classes, messages are first enqueued before processed.
So, in this thread

lock(this)    // Statemachine<br />
{<br />
    ...<br />
    lock(this)    // MessageQueue<br />
    {<br />
        ...<br />
    }<br />
}

When several events occured in different threads, I suppose all of them will be locked at the first
lock(this) // Statemachine

before processed. Will this cause a deadlock in my program ?

Guffa24-Mar-06 6:42

24-Mar-06 6:42

If those are the only lock statements in the code, and they always get called in that order, it won't cause a deadlock. But if they always get called in that order, the inner lock is of no use at all.

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Bob_Sun24-Mar-06 6:54

24-Mar-06 6:54

Guffa wrote:
If those are the only lock statements in the code, and they always get called in that order, it won't cause a deadlock. But if they always get called in that order, the inner lock is of no use at all.

First, the second lock(this) is not necessarily called every time, but when called the order is always the same. Second, the second lock(this) may also be called directly from other threads which have no relation to StateMachine(outside statemachine).

Steve Hansen24-Mar-06 1:58

Steve Hansen

24-Mar-06 1:58

lock(this) can bring you in a deadlock
instead create a field like this:
private object syncRoot = new object();
and use
lock(syncRoot)

[EDIT] Not static Smile | :)

field will be static only for static methods

Bob_Sun24-Mar-06 5:11

24-Mar-06 5:11

Thank you very much.

lock( a private object )

was the good way introduced to avoid deadlock.
But why lock(this) brings about deadlock?

I want to find the case in which my program falls into a deadlock.

Steve Hansen24-Mar-06 6:16

Steve Hansen

24-Mar-06 6:16

This article seems to mention a DeadLock
http://www.codeproject.com/csharp/lockmanager.asp

DG->GridView problem...

E.L. Golpe24-Mar-06 1:05

E.L. Golpe

24-Mar-06 1:05

I need a guru's advice: I am porting datagrids over to gridviews, and have the following old code:

<br />
            foreach (DataGridItem dgItem in dgClicks.Items)<br />
            {<br />
                CheckBox chkSelected = (CheckBox)dgItem.FindControl("chkSelection");<br />
                if (chkSelected != null && chkSelected.Checked)<br />
                {<br />
                    if (dgClicks.DataKeys[dgItem.DataSetIndex] != System.DBNull.Value)<br />
                    {<br />
                        int nTopupRequestID = (Int32)dgClicks.DataKeys[dgItem.DataSetIndex];<br />
<br />
                        BL.receipts.BlockCapturedTransaction(nTopupRequestID, edBlockReason.Text);<br />
                    }<br />
                }<br />
            }<br />

But I can't seem to figure out how to fix the second conditional in what I have written to convert.. I keep getting an operator overload error..

<br />
foreach (GridViewRow gvRow in gvClicks.Rows)<br />
            {<br />
                CheckBox chkSelected = (CheckBox)gvRow.FindControl("chkSelection");<br />
                if (chkSelected != null && chkSelected.Checked)<br />
                {<br />
                    if (gvClicks.DataKeys[gvRow.DataItemIndex] != System.DBNull.Value):confused:<br />
                    {<br />
                        int nTopupRequestID = Convert.ToInt32(gvClicks.DataKeys[gvRow.DataItemIndex]);<br />
<br />
                        BL.receipts.BlockCapturedTransaction(nTopupRequestID, edBlockReason.Text);<br />
                    }<br />
                }<br />
            }<br />

I'm sure this is an easy fix for some of yu guys.. so what did I do wrong? Is there a better way to approach this with the GridView??

Hoping for someones kind assistance!
-Eric

Practice sesquipedalianism! Wink | ;)

-- modified at 8:27 Friday 24th March, 2006
LETS SHORTEN MY QUESTION.. HOW WOULD YOU WRITE THIS WITH A GRIDVIEW, NOT A DATAGRID??

if (dgClicks.DataKeys[dgItem.DataSetIndex] != System.DBNull.Value)

About lock

Bob_Sun24-Mar-06 0:47

24-Mar-06 0:47

I have a problem about lock in C#.

I have written a multithread program, but the other day, the program hung up suddenly.
I have checked the code throughly but i could find nothing wrong.
In order to realize sync., i use lock(this) at several places.
But to my dismay, i was told this is not a good way at all recently.

Can anyone give me some information about this?

Thank you

-- modified at 6:57 Friday 24th March, 2006

Re: About lock

Guffa24-Mar-06 2:03