Remove signalfd feature in favor of conditional compilation

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.

1 files changed, 3 insertions, 7 deletions

diff --git a/src/sys/signalfd.rs b/src/sys/signalfd.rs
index a3dfb6be..fcf2efa9 100644
--- a/src/sys/signalfd.rs
+++ b/src/sys/signalfd.rs
@@ -60,12 +60,10 @@ pub fn signalfd(fd: RawFd, mask: &SigSet, flags: SfdFlags) -> Result<RawFd> {
 /// # Examples
 ///
 /// ```
-/// use nix::sys::signalfd::*;
-///
+/// # use nix::sys::signalfd::*;
+/// // Set the thread to block the SIGUSR1 signal, otherwise the default handler will be used
 /// let mut mask = SigSet::empty();
-/// mask.add(signal::SIGUSR1).unwrap();
-///
-/// // Block the signal, otherwise the default handler will be invoked instead.
+/// mask.add(signal::SIGUSR1);
 /// mask.thread_block().unwrap();
 ///
 /// // Signals are queued up on the file descriptor
@@ -74,11 +72,9 @@ pub fn signalfd(fd: RawFd, mask: &SigSet, flags: SfdFlags) -> Result<RawFd> {
 /// match sfd.read_signal() {
 ///     // we caught a signal
 ///     Ok(Some(sig)) => (),
-///
 ///     // there were no signals waiting (only happens when the SFD_NONBLOCK flag is set,
 ///     // otherwise the read_signal call blocks)
 ///     Ok(None) => (),
-///
 ///     Err(err) => (), // some error happend
 /// }
 /// ```