[tor-bugs] #23581 [Core Tor/Tor]: Die more helpfully if Schedulers option isn't compatible with platform

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#23581: Die more helpfully if Schedulers option isn't compatible with platform
------------------------------+--------------------------------
     Reporter:  pastly        |      Owner:  (none)
         Type:  defect        |     Status:  new
     Priority:  Medium        |  Milestone:  Tor: 0.3.3.x-final
    Component:  Core Tor/Tor  |    Version:
     Severity:  Normal        |   Keywords:  tor-sched
Actual Points:                |  Parent ID:
       Points:                |   Reviewer:
      Sponsor:                |
------------------------------+--------------------------------
 KIST isn't supported on OS X. The user is being dumb and setting
 `Schedulers` to just KIST, so we can't fallback to KISTLite or even
 Vanilla. Therefore `select_scheduler()` doesn't set `the_scheduler` and
 thus `the_scheduler->init()` doesn't work in `set_scheduler()`.

 This isn't a problem during a HUP because we already have a scheduler.
 `select_scheduler()` doesn't change anything and we keep on running with
 whatever scheduler we were using before.

 {{{
 cranium:tor mtraudt$ cat torrc
 DataDirectory data
 PidFile data/tor.pid
 Socks5Proxy 127.0.0.1:2343
 Schedulers KIST
 Log [sched]info [~sched]notice stdout
 }}}

 {{{
 cranium:tor mtraudt$ ./src/or/tor -f torrc
 Sep 19 09:33:26.370 [notice] Tor 0.3.2.1-alpha-dev (git-472858d629252ae8)
 running on Darwin with Libevent 2.1.8-stable, OpenSSL 1.0.2l, Zlib 1.2.5,
 Liblzma 5.2.3, and Libzstd N/A.
 Sep 19 09:33:26.371 [notice] Tor can't help you if you use it wrong! Learn
 how to be safe at https://www.torproject.org/download/download#warning
 Sep 19 09:33:26.371 [notice] This version is not a stable Tor release.
 Expect more bugs than usual.
 Sep 19 09:33:26.371 [notice] Read configuration file
 "/private/tmp/tor/torrc".
 Sep 19 09:33:26.373 [warn] Path for DataDirectory (data) is relative and
 will resolve to /private/tmp/tor/data. Is this what you wanted?
 Sep 19 09:33:26.374 [warn] Path for PidFile (data/tor.pid) is relative and
 will resolve to /private/tmp/tor/data/tor.pid. Is this what you wanted?

 ============================================================ T= 1505828006
 Tor 0.3.2.1-alpha-dev (git-472858d629252ae8) died: Caught signal 11
 0   tor                                 0x000000010a4e38d9 crash_handler +
 57
 1   libsystem_platform.dylib            0x00007fff9307d52a _sigtramp + 26
 2   tor                                 0x000000010a4d2a84 set_scheduler +
 164
 3   tor                                 0x000000010a4d34eb scheduler_init
 + 347
 4   tor                                 0x000000010a346115
 options_act_reversible + 453
 5   tor                                 0x000000010a345c24 set_options +
 68
 6   tor                                 0x000000010a350991
 options_init_from_string + 1697
 7   tor                                 0x000000010a34fa27
 options_init_from_torrc + 1399
 8   tor                                 0x000000010a42f833 tor_init + 1523
 9   tor                                 0x000000010a430147 tor_main + 103
 10  tor                                 0x000000010a2fb350 main + 48
 11  libdyld.dylib                       0x00007fff9e1765ad start + 1
 Abort trap: 6
 }}}

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/23581>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
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