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https://issues.apache.org/jira/browse/MESOS-5293?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15260606#comment-15260606
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Anand Mazumdar commented on MESOS-5293:
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This has been there for a long time before we implemented the executor
endpoint. It's just that the example mentions them. We would need to fix this
for all the slave endpoints if it turns out to be a bug. (haven't read the
description fully yet)
> Endpoint handlers for master and agent need to be implemented surprisingly
> differently
> --------------------------------------------------------------------------------------
>
> Key: MESOS-5293
> URL: https://issues.apache.org/jira/browse/MESOS-5293
> Project: Mesos
> Issue Type: Bug
> Components: master, slave
> Reporter: Benjamin Bannier
> Labels: tech-debt
>
> The way endpoints are routed is inconsistent between master and agent code
> which makes adding or extending handlers error prone.
> In the master we route like this:
> {code}
> // Setup HTTP routes.
> route("/api/v1/scheduler",
> DEFAULT_HTTP_FRAMEWORK_AUTHENTICATION_REALM,
> Http::SCHEDULER_HELP(),
> [this](const process::http::Request& request,
> const Option<string>& principal) {
> Http::log(request);
> return http.scheduler(request, principal);
> });
> {code}
> We capture a pointer to the current {{Master}} in the callback which allows
> us to access master state from an endpoint handler. The handler is a
> (probably non-static) member function of the master's member variable
> {{http}} which outlives the callback.
> Routing in the agent looks like this:
> {code}
> // Setup HTTP routes.
> Http http = Http(this);
> route("/api/v1/executor",
> Http::EXECUTOR_HELP(),
> [http](const process::http::Request& request) {
> Http::log(request);
> return http.executor(request);
> });
> {code}
> In contrast to the master code we here copy a {{Http}} by value into the
> callback. Since the callback is currently treated like a value and might
> e.g., be freely copied around we are only guaranteed that {{http}} lives long
> enough for the handler (here {{Http::executor}}) to return. In particular,
> since endpoint handlers return a {{Future<Response>}} there is no guarantee
> that the used {{http}} lives long enough to be still valid once a
> conventional (e.g., non-static member) continuation is executed.
> Both models have their merit:
> * capturing a pointer to the master simplifies reasoning about lifetimes,
> * capturing just a {{Http}} with very short lifetime minimizes interactions
> among (e.g., concurrent) invocations of endpoint handlers.
> This great inconsistency comes with a cost though, as employing patterns
> borrowed from master endpoint handlers in agent code will lead to potentially
> subtle bugs where a developer assuming that {{http}} would outlive a
> handler's execution might introduce code invoking member functions of already
> destructed variables. This is especially likely in code employing multiple
> layers of {{delay}} or {{defer}} for which compilers seem unable to detect
> lifetime problems and emit diagnostics.
> It would be great if we could to use just one of the patterns to minimize
> confusion, e.g., the more straight-forward master pattern.
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