There were a few random places where 0 was being used as a null pointer
constant.

We have a NULL macro for this very purpose, use it.

There is also some interest in actually deprecating the use of 0 as a
null pointer constant in C.

This was found with -Wzero-as-null-pointer-constant which was enabled
for C in GCC 15 (not enabled with Wall or Wextra... yet).

Link: <https://gcc.gnu.org/bugzilla/show_bug.cgi?id=117059>

libcrypt is no longer part of glibc, so it might not be available.

Signed-off-by: Piotr Sikora <piotr@aviatrix.com>

Notably, Apple Silicon CPUs have 128 byte cache line size,
which is twice the default configured for generic aarch64.

Signed-off-by: Piotr Sikora <piotr@aviatrix.com>

The old code was breaking strict aliasing rules.

Signed-off-by: Piotr Sikora <piotr@aviatrix.com>

Each AIO (thread IO) operation being run is now accompanied with 1-minute
timer.  This timer prevents unexpected shutdown of the worker process while
an AIO operation is running, and logs an alert if the operation is running
for too long.

This fixes "open socket left" alerts during worker processes shutdown
due to pending AIO (or thread IO) operations while corresponding requests
have no timers.  In particular, such errors were observed while reading
cache headers (ticket #2162), and with worker_shutdown_timeout.

When graceful shutdown was requested, and then nginx was forced to
do fast shutdown, it used to (incorrectly) complain about open sockets
left in connections which weren't yet closed when fast shutdown
was requested.

Fix is to avoid complaining about open sockets when fast shutdown was
requested after graceful one.  Abnormal termination, if requested with
the WINCH signal, can still happen though.

rand() is used on win32. RAND_MAX is implementation defined. win32's is
0x7fff.

Existing uses of ngx_random() rely upon 0x7fffffff range provided by
POSIX implementations of random().

MTU selection starts by doubling the initial MTU until the first failure.
Then binary search is used to find the path MTU.