"Got signal before environment was installed on our thread"

[Dima Pasechnik]

Discussing the issue with GC people here
https://github.com/ivmai/bdwgc/issues/180

On Fri, Sep 22, 2017 at 1:14 PM, Daniel Kochmański <daniel at turtleware.eu> wrote:
> On 22.09.2017 13:31, Dima Pasechnik wrote:
>>
>> No, we have not done that before, and everything worked on Linux and
>> OSX, and even on Cygwin (that is to say, we were lucky with threads
>> implementations on these platforms, depending on some sort of
>> undefined behaviour). Now I am trying
>> ecl_import_current_thread/ecl_release_current_thread on FreeBSD, and
>> it certainly appears to be the right direction, but I have a couple of
>> questions, at least one of them related to signal handling.
>>
>> 0) any advice on signal flags to be set to certain values?
>> Namely, ECL_OPT_SIGNAL_HANDLING_THREAD and
>> ECL_OPT_THREAD_INTERRUPT_SIGNAL? They seem to affect
>> the setup quite a bit; I had to do some trial and error, setting the
>> former to 1 and the latter to 67 (probably OS-specific value) seemed
>> to have done the trick...
>>
>> 1) as ECL must be built with --enable-threads, does it mean
>> that it will also try to spawn threads on its own?
>> (so far we always used to --disable-threads; for debugging purposes
>> I'd rather not let ECL run its own threads)
>>
>> [I'd say this is a documentation issue, too, as it's not clear what
>> exactly --enable-threads is doing: enabling own ECL's threads, or
>> enabling ECL embedding in a multithreaded program, or both?]
>
> --enable-threads gives ECL ability to use threads (i.e programmer may create
> his own
> thread in Lisp program). ECL may be embedded in any scenario (having both
> threads enabled
> and disabled), but if threads for ECL are disabled, than it is calling
> program responsibility to
> assure that ECL is accessed synchronously (i.e no two functions in ECL at
> the same time are called).
>
> ECL_OPT_SIGNAL_HANDLING_THREAD is a flag, which when set to 1 makes ECL
> create
> a separate thread meant for handling signals (so ECL in that case runs two
> threads). If
> ECL has threads disabled, then this flag does nothing.
>
>>
>> 2) for some reason calling ecl_release_current_thread()
>> leads to a nasty  crash, with lines like
>>
>>      frame #299974: 0x0000000883a52463
>> libecl.so.16.1`FElibc_error(msg="", narg=0) at error.d:490
>>      frame #299975: 0x0000000883ab3e2c libecl.so.16.1`ecl_process_env
>> at process.d:70
>>      frame #299976: 0x0000000883aba9d4
>> libecl.so.16.1`ecl_alloc_compact_object(t=t_base_string,
>> extra_space=12) at alloc_2.d:622
>>      frame #299977: 0x0000000883a8c782
>> libecl.so.16.1`ecl_alloc_simple_vector(l=11, aet=ecl_aet_bc) at
>> array.d:585
>>      frame #299978: 0x0000000883a5331d
>> libecl.so.16.1`make_base_string_copy(s="No error: 0") at string.d:136
>>      frame #299979: 0x0000000883a52320
>> libecl.so.16.1`_ecl_strerror(code=0) at error.d:475
>>      frame #299980: 0x0000000883a52463
>>
>> repeating endlessly in the backtrace.
>> Must it be called at all?
>> (The test program in examples you pointed at does work for me, with
>> few makefile changes...)
>>
>>
>>
>> 3) How does one call cl_boot() in such a multithreaded setting? I
>> tried merely putting the call to
>>
>>     ecl_import_current_thread()
>>
>> before the call to
>>
>>     cl_boot()
>>
>> but I get an error from GC:
>>
>> "Threads explicit registering is not previously enabled"
>> and the program aborts.
>> Without doing ecl_import_current_thread(), cl_boot() succeeds in "main"
>> thread,
>> but coredumps if invoked from another thread---this is the behaviour
>> you mistook for another instance of GC kicking in)
>>
>> While we probably can live with cl_boot() always being called in the
>> main thread, this would be an extra burden to implement...
>
> ecl_import_current_thread and ecl_release_current_thread needs to be called
> in threads, which call ECL and are different than thread where cl_boot is
> called.
> For the thread where cl_boot was called you don't call import/release, they
> are
> implicit for cl_boot / cl_shutdown. You may run cl_boot in thread not being
> main
> one, that's not the issue.
>>
>>
>> 4) GC_THREADS is #define'd both in ECL and in GC headers.
>> This seems wrong to me.
>
> No idea why it is that way. I'll keep in mind investigating that.
>
> Regards,
> Daniel