https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107874
--- Comment #13 from Jerry DeLisle <jvdelisle at gcc dot gnu.org> --- A debug session gives: (gdb) c Continuing. ^C Program received signal SIGINT, Interrupt. futex_wait (private=0, expected=2, futex_word=0x405950) at ../sysdeps/nptl/futex-internal.h:146 146 int err = lll_futex_timed_wait (futex_word, expected, NULL, private); (gdb) bt #0 futex_wait (private=0, expected=2, futex_word=0x405950) at ../sysdeps/nptl/futex-internal.h:146 #1 __GI___lll_lock_wait (futex=futex@entry=0x405950, private=0) at lowlevellock.c:49 #2 0x00007ffff79d1432 in lll_mutex_lock_optimized (mutex=0x405950) at pthread_mutex_lock.c:48 #3 ___pthread_mutex_lock (mutex=0x405950) at pthread_mutex_lock.c:93 #4 0x00007ffff7e73503 in __gthread_mutex_lock (__mutex=0x405950) at ../libgcc/gthr-default.h:749 #5 get_gfc_unit (n=6, do_create=1) at ../../../trunk/libgfortran/io/unit.c:395 #6 0x00007ffff7e71b85 in data_transfer_init (dtp=0x7fffffffd9d0, read_flag=0) at ../../../trunk/libgfortran/io/transfer.c:3007 #7 0x00000000004017dd in testmerge9::tstuff () at merge_1.f90:39 #8 0x000000000040128c in testmerge9 () at merge_1.f90:14 #9 0x000000000040184f in main (argc=1, argv=0x7fffffffe2c4) at merge_1.f90:36 #10 0x00007ffff796a510 in __libc_start_call_main ( main=main@entry=0x40181b <main>, argc=argc@entry=1, argv=argv@entry=0x7fffffffdfa8) at ../sysdeps/nptl/libc_start_call_main.h:58 #11 0x00007ffff796a5c9 in __libc_start_main_impl (main=0x40181b <main>, argc=1, argv=0x7fffffffdfa8, init=<optimized out>, fini=<optimized out>, rtld_fini=<optimized out>, stack_end=0x7fffffffdf98) at ../csu/libc-start.c:381 I would speculate we are trashing some memory since there is no reason to hang in there.