Fix thread safety issues in aio, chdir, and wait tests

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

1 files changed, 12 insertions, 0 deletions

diff --git a/test/test.rs b/test/test.rs
index 2cf30360..4c81aa2b 100644
--- a/test/test.rs
+++ b/test/test.rs
@@ -25,6 +25,7 @@ mod test_unistd;
 
 use nixtest::assert_size_of;
 use std::os::unix::io::RawFd;
+use std::sync::Mutex;
 use nix::unistd::read;
 
 /// Helper function analogous to std::io::Read::read_exact, but for `RawFD`s
@@ -37,6 +38,17 @@ fn read_exact(f: RawFd, buf: &mut  [u8]) {
     }
 }
 
+lazy_static! {
+    /// Any test that changes the process's current working directory must grab
+    /// this mutex
+    pub static ref CWD_MTX: Mutex<()> = Mutex::new(());
+    /// Any test that creates child processes must grab this mutex, regardless
+    /// of what it does with those children.
+    pub static ref FORK_MTX: Mutex<()> = Mutex::new(());
+    /// Any test that registers a SIGUSR2 handler must grab this mutex
+    pub static ref SIGUSR2_MTX: Mutex<()> = Mutex::new(());
+}
+
 #[test]
 pub fn test_size_of_long() {
     // This test is mostly here to ensure that 32bit CI is correctly