synchronization problem with rpc calls

Hi,

my chess application allows users to create game invitations to other users. To accept such an invitation, the invited user has to click on a hyperlink/anchor called "Accept". This will trigger a RPC call to the server, and the server will create a new game based on the invitation.

However, sometimes two games are created for the same invitation, with nearly the same starting time. The starting times differ in less than a second.

My assumption is the following: The invited user made a double click on the hyperlink, which caused the browser to generate two rpc calls. Is this possible? I would have expected that a browser will not generate a second HTTP request while another one is pending? Would you agree that this the explanation for the problem?

If so, then there is a piece of code on the server that gets executed in different threads, i. e. in parallel, potentially. So we need a kind of semaphore, to detect if we are actually creating a game for an invitation, where another game is already created in another thread.

What would be a good, elegant approach to do that? In theory we need some atomic test-and-set method. In single-threaded code we used a static variable. But how do we do this in muti-threaded GWT/RPC-code?

Thanks

Magnus

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