1559268 - Implement Service Workers' about:debugging "Inspect" with dom.serviceWorkers.parent_intercept=true

Status: RESOLVED FIXED

(DevTools :: about:debugging, task, P3)

Comment 1

[Perry Jiang [:perry] [no longer employee, use ni?]]

Attachment: Bug 1559268 - WIP

Comment 2

[BugBot [:suhaib / :marco/ :calixte]]

Bugbug thinks this bug is a task, but please change it back in case of error.

Comment 3

[Perry Jiang [:perry] [no longer employee, use ni?]]

What the problem is:

Service Workers may be terminated when they're idle, i.e. they've handled an event and there are no more subsequent events dispatched. For debugging purposes, this isn't a desirable behavior. To keep a Service Worker alive when the toolbox opens, the current code on trunk calls nsIServiceWorkerInfo.attachDebugger [1]; nsIServiceWorkerInfo.detachDebugger is then called when the toolbox closes [2].

This works fine when the nsIServiceWorkerInfo and the worker (and thus its corresponding WorkerTargetActor) exist in the same process; this is the case for on-trunk code, regardless of the dom.serviceWorkers.parent_intercept pref's value (if the pref is on, they'll all exist in the parent process, and if it's off, they'll all exist in a content process).

With all that said, the actual problem is that once the "new implementation" (waiting in bug 1231213) lands, dom.serviceWorkers.parent_intercept=true will be so that the nsIServiceWorkerInfo and its corresponding worker exist in separate processes. Service Workers will all exist in content processes but be "controlled" from the parent, which means the nsIServiceWorkerInfo will exist in the parent, while the WorkerTargetActor will exist in a content process. So, we'd like a way to make a cross-process call to nsIServiceWorkerInfo.{attach,detach}debugger when the toolbox opens/closes.

The fix

The WIP patch shows what a fix might look like, but it doesn't work due to the setupInParent not being available to anything other than Frame and WebExtensions actors (I think). This idea is just to replace the in-process calls in [1] and [2] with cross-process/message manager/IPC calls. A worker and its corresponding nsIServiceWorkerInfo will have the same ID (depending on bug 1552945's patches), so the nsIServiceWorkerInfo could be obtained by enumerating all nsIServiceWorkerRegistrationInfos in the parent and matching agains their active workers' ID.

Another idea (discussed at All Hands) is to pass an identifier of a worker's registration in the toolbox URL. The attachDebugger method can be called via nsIServiceWorkerRegistrationInfo.activeWorker.attachDebugger, and the worker's ID can be obtained via nsIServiceWorkerRegistrationInfo.activeWorker.id, which can be used (I think) to get the WorkerTargeActor.

[1] https://searchfox.org/mozilla-central/rev/928742d3ea30e0eb4a8622d260041564d81a8468/devtools/server/actors/targets/worker.js#68
[2] https://searchfox.org/mozilla-central/rev/928742d3ea30e0eb4a8622d260041564d81a8468/devtools/server/actors/targets/worker.js#178

Comment 4

[Julian Descottes [:jdescottes]]

Attachment: Bug 1559268 - Prevent service worker shutdown while debugging in parent-intercept mode

Comment 5

[Pulsebot]

Pushed by [e-mail]:
https://hg.mozilla.org/mozilla-central/rev/41e0d5d0947e
Prevent service worker shutdown while debugging in parent-intercept mode r=ochameau,perry

Comment 6

[Daniel Varga [:dvarga]]

https://hg.mozilla.org/mozilla-central/rev/41e0d5d0947e