Comment 1 for bug 1438702

Got it to happen locally (clang on arm64):

(gdb) info threads
  Id Target Id Frame
  7 Thread 0x7f11e661b700 (LWP 27521) ".mir_acceptance" 0x00007f11ea4b08ed in pthread_join (threadid=139714606655952,
    thread_return=0x0) at pthread_join.c:90
  6 Thread 0x7f11e5ad2700 (LWP 27529) "Mir/Snapshot" pthread_cond_wait@@GLIBC_2.3.2 ()
    at ../sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
  5 Thread 0x7f11d7fff700 (LWP 27532) "Mir/IPC" 0x00007f11ea1e54f3 in epoll_wait ()
    at ../sysdeps/unix/syscall-template.S:81
  4 Thread 0x7f11e50a8700 (LWP 27533) "Mir/IPC" pthread_cond_wait@@GLIBC_2.3.2 ()
    at ../sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
  3 Thread 0x7f11e48a7700 (LWP 27534) "Mir/Comp" pthread_cond_wait@@GLIBC_2.3.2 ()
    at ../sysdeps/unix/sysv/linux/x86_64/pthread_cond_wait.S:185
  2 Thread 0x7f11d77fe700 (LWP 27535) "Mir/Input" 0x00007f11ea1e54f3 in epoll_wait ()
    at ../sysdeps/unix/syscall-template.S:81
* 1 Thread 0x7f11ee98d840 (LWP 27438) ".mir_acceptance" 0x00007f11ea4b08ed in pthread_join (threadid=139714856335824,
    thread_return=0x0) at pthread_join.c:90