[tahoe-lafs-trac-stream] [Tahoe-LAFS] #3883: The dependency of allmydata.stats.CPUUsageMonitor on foolscap is unnecessary

[Tahoe-LAFS]

#3883: The dependency of allmydata.stats.CPUUsageMonitor on foolscap is
unnecessary
---------------------+---------------------------
 Reporter:  exarkun  |          Owner:
     Type:  defect   |         Status:  new
 Priority:  normal   |      Milestone:  undecided
Component:  code     |        Version:  n/a
 Keywords:           |  Launchpad Bug:
---------------------+---------------------------
 `allmydata.stats.CPUUsageMonitor` uses `foolscap.api.eventually` to
 schedule collection of "the initial process CPU usage value" so that it is
 collected only after the reactor has started - which corresponds to a time
 after daemonization has completed and the right process will be sampled.

 This is obsolete because Tahoe no longer uses `.tac` files to start up and
 no longer offers any bespoke daemonization functionality itself.

 `CPUUsageMonitor` can just sample the process CPU usage on construction or
 in `startService`.

 Removing the Foolscap dependency here simplifies and shortens the code.

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Ticket URL: <https://tahoe-lafs.org/trac/tahoe-lafs/ticket/3883>
Tahoe-LAFS <https://Tahoe-LAFS.org>
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