Invalid memory access in Fibers

[bararchy]

lldb:

* thread #1, name = 'my_program', stop reason = signal SIGSEGV: invalid address (fault address: 0x0)
    frame #0: my_program`__crystal_main at fiber.cr:74
   71  	    {% end %}
   72  	
   73  	    @prev_fiber = nil
-> 74  	    if last_fiber = @@last_fiber
   75  	      @prev_fiber = last_fiber
   76  	      last_fiber.next_fiber = @@last_fiber = self
   77  	    else
(lldb) bt
* thread #1, name = 'my_program', stop reason = signal SIGSEGV: invalid address (fault address: 0x0)
  * frame #0: my_program`__crystal_main at fiber.cr:74
    frame #1: my_program`main at main.cr:12
    frame #2: 0x00007ffff60ee511 libc.so.6`__libc_start_main + 241
    frame #3: 0x0000555555556dfa my_program`_start + 42

Crash without debugger:

Invalid memory access (signal 11) at address 0x0
[0x55e848c9eb56] ???
[0x55e848c64b20] __crystal_sigfault_handler +32
[0x7f350d775fe0] ???
[0x55e848c45932] ???
[0x55e848c645be] main +46
[0x7f350cb73511] __libc_start_main +241
[0x55e848c42dfa] _start +42
[0x0] ???

[kostya]

may be related: #3900

[bararchy]

@kostya I do use IO.select , should it be avoided ?

[RX14]

IO.select should be removed anyway as it blocks the event loop.

[bararchy]

Removing Select from my code and adding more checks indeed made this thing go away