Second sketch for mechanism to cancel DcmSCU negotiateAssociation before connectionTimeout elapses #79
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added 6 commits
April 17, 2023 08:46
… for cancelation of TCP connect attempts Here we extend the DUL_ASSOCIATESERVICEPARAMETERS struct with members for: * A cancelation callback function that can be implemented by client to cancel ongoing TCP connect attempts * A poll/select interval that is used to chop the poll/select timeout into shorter intervals to enable checking for cancelation.
This is implemented using a cancellation callback (not a cancellation flag). The reason for using a cancellation callback function is that this relieves the dul implementation from having to deal with potential data races related to a cancellation flag. It is now up to the caller to ensure appropriate synchronization of any data being involved in cancellation.
…s argument We'll use this cancel token to cancel ongoing TCP connect attempts. A cancel token allows the client to decide how a request should be cancelled, for example using std::stop_token in the implementation of the ICancelToken.
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If a server is unavailable, the DcmSCU::negotiateAssociation function call will block for the duration of the connectionTimeout. In many cases this timeout may be long, 30-60 seconds to ensure that we can robustly establish associations against slow servers. This is a long time for a user to wait for a device to shut down.
In some use cases, for example for portable imaging devices, the ability to quickly shut down is important to reduce the risk of the user pulling the power cable before the system is completely shut down. Such devices typically have a high risk that servers are temporarily unavailable, for example if they are serving multiple purposes and have to be moved from lab to lab.
This pull request adds support for early cancellation of TCP connect attempts by introducing a TCP poll interval and a cancellation callback to DUL_ASSOCIATESERVICEPARAMETERS. The requestAssociationTCP function will call the cancellation callback at intervals specified by the polling interval and allows the caller to decide if the TCP connect attempt should be cancelled.
On the DcmSCU level, DcmSCU::negotiateAssociation is changed to take a cancelation token as an optional argument, and allows the client to implement its own cancellation mechanism.
This draft has some weaknesses: