Parent process hangs on:
* thread #1, queue = 'com.apple.main-thread', stop reason = signal SIGSTOP
  * frame #0: 0x00007fff6741181e libsystem_kernel.dylib`read + 10
    frame #1: 0x000000010226a117 python.exe`_Py_read(fd=3, buf=0x00007f8d24009840, count=8192) at fileutils.c:1744:13
    frame #2: 0x00000001022f1335 python.exe`_io_FileIO_readinto_impl(self=0x0000000103b284d0, buffer=0x00007ffeedcbe928) at fileio.c:645:9
    frame #3: 0x00000001022f063e python.exe`_io_FileIO_readinto(self=0x0000000103b284d0, arg=0x0000000102f5d090) at fileio.c.h:205:20
    frame #4: 0x00000001020050e9 python.exe`method_vectorcall_O(func=0x00000001026fd970, args=0x00007ffeedcbeaf0, nargsf=2, kwnames=0x0000000000000000) at descrobject.c:462:24
    frame #5: 0x0000000101ff323d python.exe`_PyObject_VectorcallTstate(tstate=0x00007f8d20d04f00, callable=0x00000001026fd970, args=0x00007ffeedcbeaf0, nargsf=2, kwnames=0x0000000000000000) at abstract.h:114:11
    frame #6: 0x0000000101ff30c9 python.exe`PyObject_VectorcallMethod(name=0x00000001026fcbe0, args=0x00007ffeedcbeaf0, nargsf=2, kwnames=0x0000000000000000) at call.c:770:24
    frame #7: 0x00000001022f92a0 python.exe`PyObject_CallMethodOneArg(self=0x0000000103b284d0, name=0x00000001026fcbe0, arg=0x0000000102f5d090) at abstract.h:204:12

where "name" in frame #7 is the "readinto" method of <_io.FileIO name=3 mode='rb' closefd=True> and "arg" is <memory at 0x102f5d090>.


Child process hangs on:

* thread #1, queue = 'com.apple.main-thread', stop reason = signal SIGSTOP
  * frame #0: 0x00007fff67413bf6 libsystem_kernel.dylib`write + 10
    frame #1: 0x000000010226a3e0 python.exe`_Py_write_impl(fd=2, buf=0x00007ffeedcbcbcb, count=1, gil_held=0) at fileutils.c:1813:17
    frame #2: 0x000000010226a535 python.exe`_Py_write_noraise(fd=2, buf=0x00007ffeedcbcbcb, count=1) at fileutils.c:1871:12
    frame #3: 0x0000000102257834 python.exe`_Py_DumpASCII(fd=2, text=0x0000000102a1bed0) at traceback.c:1002:13
    frame #4: 0x0000000102258ba5 python.exe`dump_frame(fd=2, frame=0x00000001025dbba8) at traceback.c:1035:9
    frame #5: 0x00000001022579fa python.exe`dump_traceback(fd=2, tstate=0x00007f8d20d04f00, write_header=0) at traceback.c:1084:9
    frame #6: 0x0000000102257bc6 python.exe`_Py_DumpTracebackThreads(fd=2, interp=0x00007f8d2281b010, current_tstate=0x00007f8d20d04f00) at traceback.c:1186:9
    frame #7: 0x0000000102311dc3 python.exe`faulthandler_dump_traceback(fd=2, all_threads=1, interp=0x00007f8d2281b010) at faulthandler.c:245:15
    frame #8: 0x000000010231224b python.exe`faulthandler_user(signum=14) at faulthandler.c:843:5
    frame #9: 0x00007fff674c85fd libsystem_platform.dylib`_sigtramp + 29
    frame #10: 0x00007fff6741435f libsystem_kernel.dylib`__ioctl + 11
    frame #11: 0x00007fff6741434b libsystem_kernel.dylib`ioctl + 150
    frame #12: 0x00007fff6734ad63 libsystem_c.dylib`tcsetattr + 111
    frame #13: 0x0000000103c772ee libreadline.8.dylib`_set_tty_settings + 28
    frame #14: 0x0000000103c76d87 libreadline.8.dylib`rl_prep_terminal + 683
    frame #15: 0x0000000103c88ce9 libreadline.8.dylib`_rl_callback_newline + 51
    frame #16: 0x0000000103c5ae75 readline.cpython-311d-darwin.so`readline_until_enter_or_signal(prompt="prompt", signal=0x00007ffeedcbd63c) at readline.c:1318:5
    frame #17: 0x0000000103c58637 readline.cpython-311d-darwin.so`call_readline(sys_stdin=0x00007fff8d9c8d90, sys_stdout=0x00007fff8d9c8e28, prompt="prompt") at readline.c:1396:9
    frame #18: 0x0000000101fad9b6 python.exe`PyOS_Readline(sys_stdin=0x00007fff8d9c8d90, sys_stdout=0x00007fff8d9c8e28, prompt="prompt") at myreadline.c:391:14
    frame #19: 0x00000001021a071d python.exe`builtin_input_impl(module=0x000000010268c0b0, prompt=0x00000001027a0400) at bltinmodule.c:2188:13