[1]

(1.1)
child:  XX
parent: DD

(1.2)
child:  XDXD
parent: XDXD

(1.3)
child:  XX
parent: DD

(1.4)
child:  XDXD
parent: XDXD

(1.5)
child:  XDXD
parent: BLANK

[2]

(2.1)
B
C

(2.2)
B
D
F

(2.3) UNPREDICTABLE, see output below:
F
@E\x85\xd9ڠ\xff\xff
B

[3]

Possible answers:

1) signal() may restart sem_wait(), leading to unbounded wait

2) There is a race condition: SIGALRM may be delivered after we call alarm()
   but before sem_wait()

3) SIGALRM may have been blocked before calling sem_wait_with_timeout()

4) sem_wait_with_timeout() would cancel an existing alarm, if there was one

5) A pending alarm could arrive after signal() but before alarm(timeout).
   Depending on the system, this could reset the SIGALRM handler.

6) sem_wait_with_timeout() replaces the existing SIGALRM disposition

7) sem_wait() could be interrupted by a different signal, which causes
   a race condition with alarm(0). This could incorrectly set errno
   to ETIMEDOUT.

[4]

(4.1) False

(4.2) False

(4.3) True

(4.4) True

(4.5) False