Note that this is now only available for Linux as support is missing in libc
for Android (see rust-lang/libc#671).
As part of this work the SIGUSR2 signal mutex was altered to be a general
signal mutex. This is because all signal handling is shared across all threads
in the Rust test harness, so if you alter one signal, depending on whether it's
additive or may overwrite the mask for other signals, it could break the other
ones. Instead of putting this on the user, just broaden the scope of the mutex
so that any altering of signal handling needs to use it.
They have four problems:
* The chdir tests change the process's cwd, which is global. Protect them
all with a mutex.
* The wait tests will reap any subprocess, and several tests create
subprocesses. Protect them all with a mutex so only one
subprocess-creating test will run at a time.
* When a multithreaded test forks, the child process can sometimes block in
the stack unwinding code. It blocks on a mutex that was held by a
different thread in the parent, but that thread doesn't exist in the
child, so a deadlock results. Fix this by immediately calling
std::process:exit in the child processes.
* My previous attempt at thread safety in the aio tests didn't work, because
anonymous MutexGuards drop immediately. Fix this by naming the
SIGUSR2_MTX MutexGuards.
Fixes#251
std::fs::File closes the underlying file descriptor on Drop, without
checking for errors. test_lseek and test_lseek64 also manually close
the file descriptor. That works for single threaded test runs. But for
multithreaded runs, it causes EBADF errors in other tests. Fix the
tests by consuming the File with into_raw_fd(), so its drop method will
never be called.
Also, fix a potential short read bug in the same tests.
test_getsockname used an IPv4 socket and assumed that localhost was
"127.0.0.1". But that assumption doesn't hold on IPv6-only hosts or on
shared-IP FreeBSD jails. Unfortunately, the Rust standard library
doesn't provide a good way to resolve localhost. So change the test to
use a unix-domain socket instead.
