Vw Diagnostic Channel List

[Florentina Holcombe]

Itis intended that a module writer wanting to report diagnostics messageswill create one or many top-level channels to report messages through.Channels may also be acquired at runtime but it is not encourageddue to the additional overhead of doing so. Channels may be exported forconvenience, but as long as the name is known it can be acquired anywhere.

If you intend for your module to produce diagnostics data for others toconsume it is recommended that you include documentation of what namedchannels are used along with the shape of the message data. Channel namesshould generally include the module name to avoid collisions with data fromother modules.

Register a message handler to subscribe to this channel. This message handlerwill be run synchronously whenever a message is published to the channel. Anyerrors thrown in the message handler will trigger an 'uncaughtException'.

Creates a TracingChannel wrapper for the givenTracingChannel Channels. If a name is given, the corresponding tracingchannels will be created in the form of tracing:$name:$eventType whereeventType corresponds to the types of TracingChannel Channels.

The class Channel represents an individual named channel within the datapipeline. It is used to track subscribers and to publish messages when thereare subscribers present. It exists as a separate object to avoid channellookups at publish time, enabling very fast publish speeds and allowingfor heavy use while incurring very minimal cost. Channels are created withdiagnostics_channel.channel(name), constructing a channel directlywith new Channel(name) is not supported.

When channel.runStores(context, ...) is called, the given context datawill be applied to any store bound to the channel. If the store has already beenbound the previous transform function will be replaced with the new one.The transform function may be omitted to set the given context data as thecontext directly.

Applies the given data to any AsyncLocalStorage instances bound to the channelfor the duration of the given function, then publishes to the channel withinthe scope of that data is applied to the stores.

If a transform function was given to channel.bindStore(store) it will beapplied to transform the message data before it becomes the context value forthe store. The prior storage context is accessible from within the transformfunction in cases where context linking is required.

The context applied to the store should be accessible in any async code whichcontinues from execution which began during the given function, howeverthere are some situations in which context loss may occur.

The class TracingChannel is a collection of TracingChannel Channels whichtogether express a single traceable action. It is used to formalize andsimplify the process of producing events for tracing application flow.diagnostics_channel.tracingChannel() is used to construct aTracingChannel. As with Channel it is recommended to create and reuse asingle TracingChannel at the top-level of the file rather than creating themdynamically.

Trace a synchronous function call. This will always produce a start eventand end event around the execution and may produce an error eventif the given function throws an error. This will run the given function usingchannel.runStores(context, ...) on the start channel which ensures allevents should have any bound stores set to match this trace context.

To ensure only correct trace graphs are formed, events will only be publishedif subscribers are present prior to starting the trace. Subscriptions which areadded after the trace begins will not receive future events from that trace,only future traces will be seen.

Trace a promise-returning function call. This will always produce astart event and end event around the synchronous portion of thefunction execution, and will produce an asyncStart event andasyncEnd event when a promise continuation is reached. It may alsoproduce an error event if the given function throws an error or thereturned promise rejects. This will run the given function usingchannel.runStores(context, ...) on the start channel which ensures allevents should have any bound stores set to match this trace context.

Trace a callback-receiving function call. The callback is expected to followthe error as first arg convention typically used. This will always produce astart event and end event around the synchronous portion of thefunction execution, and will produce a asyncStart event andasyncEnd event around the callback execution. It may also produce anerror event if the given function throws or the first argument passed tothe callback is set. This will run the given function usingchannel.runStores(context, ...) on the start channel which ensures allevents should have any bound stores set to match this trace context.

A TracingChannel is a collection of several diagnostics_channels representingspecific points in the execution lifecycle of a single traceable action. Thebehavior is split into five diagnostics_channels consisting of start,end, asyncStart, asyncEnd, and error. A single traceable action willshare the same event object between all events, this can be helpful formanaging correlation through a weakmap.

These event objects will be extended with result or error values whenthe task "completes". In the case of a synchronous task the result will bethe return value and the error will be anything thrown from the function.With callback-based async functions the result will be the second argumentof the callback while the error will either be a thrown error visible in theend event or the first callback argument in either of the asyncStart orasyncEnd events.

To ensure only correct trace graphs are formed, events should only be publishedif subscribers are present prior to starting the trace. Subscriptions which areadded after the trace begins should not receive future events from that trace,only future traces will be seen.

The start event represents the point at which a function is called. At thispoint the event data may contain function arguments or anything else availableat the very start of the execution of the function.

The end event represents the point at which a function call returns a value.In the case of an async function this is when the promise returned not when thefunction itself makes a return statement internally. At this point, if thetraced function was synchronous the result field will be set to the returnvalue of the function. Alternatively, the error field may be present torepresent any thrown errors.

It is recommended to listen specifically to the error event to track errorsas it may be possible for a traceable action to produce multiple errors. Forexample, an async task which fails may be started internally before the syncpart of the task then throws an error.

The asyncStart event represents the callback or continuation of a traceablefunction being reached. At this point things like callback arguments may beavailable, or anything else expressing the "result" of the action.

The asyncEnd event represents the callback of an asynchronous functionreturning. It's not likely event data will change after the asyncStart event,however it may be useful to see the point where the callback completes.

The error event represents any error produced by the traceable functioneither synchronously or asynchronously. If an error is thrown in thesynchronous portion of the traced function the error will be assigned to theerror field of the event and the error event will be triggered. If an erroris received asynchronously through a callback or promise rejection it will alsobe assigned to the error field of the event and trigger the error event.

It is possible for a single traceable function call to produce errors multipletimes so this should be considered when consuming this event. For example, ifanother async task is triggered internally which fails and then the sync partof the function then throws and error two error events will be emitted, onefor the sync error and one for the async error.

Does anyone know how the "Diagnostic Channel" feature in v4.1 of WLC code can be used to troubleshoot client issues? Once I check the checkbox in the WLAN Advanced properties tab, what are the next steps? Do I need to do anything on the client(s)? Where do I find the logging information the diagnostics produce?

I thought the diagnostic channel is used when you are having problems with that WLAN, i.e., that it creates a separate channel between the client(s) and WLAN for sending client-side diagnostic data to the WLC.

I'm trying to find the best 2.4 ghz channel to use in a neighborhood with way too many wifi routers. It seems like Wireless Diagnostic's "Best 2.4 Ghz" channel feature would help with this, but I'm not sure I can trust it. It often recommends Channel 2, which is right up against Channel 1, and that's the default channel that routers typically get set to. Logically then, it seems like Channel 2 would get a lot of interference, and would be one of the WORST channels to use, as opposed to something like 8 or 9 which don't show up in the wireless network list as often. Am I missing something as far as the rationale for best channel selection?

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