Make the chdir tests thread safe

The both change their process's cwd, which is global.  Handle this by
running the tests in subprocesses.

Author: asomers

test/test_unistd.rs

@@ -8,12 +8,26 @@ use std::iter;
 use std::ffi::CString;
 use std::fs::File;
 use std::io::{Write, Read};
+use std::ops::Fn;
 use std::os::unix::prelude::*;
 use std::env::current_dir;
 use tempfile::tempfile;
 use tempdir::TempDir;
 use libc::off_t;
 
+fn test_in_subprocess<F: Fn()>(func: F) {
+    let pid = fork();
+    match pid {
+        Ok(Child) => {
+            func();
+        }
+        Ok(Parent{child}) => {
+            assert_eq!(waitpid(child, None), Ok(WaitStatus::Exited(child, 0)))
+        }
+        Err(_) => panic!("Error: fork")
+    }
+}
+
 #[test]
 fn test_fork_and_waitpid() {
     let pid = fork();
@@ -42,18 +56,22 @@ fn test_fork_and_waitpid() {
 
 #[test]
 fn test_wait() {
-    let pid = fork();
-    match pid {
-        Ok(Child) => {} // ignore child here
-        Ok(Parent { child }) => {
-            let wait_status = wait();
-
-            // just assert that (any) one child returns with WaitStatus::Exited
-            assert_eq!(wait_status, Ok(WaitStatus::Exited(child, 0)));
-        },
-        // panic, fork should never fail unless there is a serious problem with the OS
-        Err(_) => panic!("Error: Fork Failed")
-    }
+    // wait could reap a different test's child process
+    test_in_subprocess(|| {
+        let pid = fork();
+        match pid {
+            Ok(Child) => {} // ignore child here
+            Ok(Parent { child }) => {
+                let wait_status = wait();
+
+                // just assert that (any) one child returns with WaitStatus::Exited
+                assert_eq!(wait_status, Ok(WaitStatus::Exited(child, 0)));
+            },
+            // panic, fork should never fail unless there is a serious problem
+            // with the OS
+            Err(_) => panic!("Error: Fork Failed")
+        }
+    });
 }
 
 #[test]
@@ -144,40 +162,41 @@ macro_rules! execve_test_factory(
 
 #[test]
 fn test_fchdir() {
-    let tmpdir = TempDir::new("test_fchdir").unwrap();
-    let tmpdir_path = tmpdir.path().canonicalize().unwrap();
-    let tmpdir_fd = File::open(&tmpdir_path).unwrap().into_raw_fd();
-    let olddir_path = getcwd().unwrap();
-    let olddir_fd = File::open(&olddir_path).unwrap().into_raw_fd();
-
-    assert!(fchdir(tmpdir_fd).is_ok());
-    assert_eq!(getcwd().unwrap(), tmpdir_path);
+    // fchdir changes the process's cwd
+    test_in_subprocess(|| {
+        let tmpdir = TempDir::new("test_fchdir").unwrap();
+        let tmpdir_path = tmpdir.path().canonicalize().unwrap();
+        let tmpdir_fd = File::open(&tmpdir_path).unwrap().into_raw_fd();
 
-    assert!(fchdir(olddir_fd).is_ok());
-    assert_eq!(getcwd().unwrap(), olddir_path);
+        assert!(fchdir(tmpdir_fd).is_ok());
+        assert_eq!(getcwd().unwrap(), tmpdir_path);
 
-    assert!(close(olddir_fd).is_ok());
-    assert!(close(tmpdir_fd).is_ok());
+        assert!(close(tmpdir_fd).is_ok());
+    });
 }
 
 #[test]
 fn test_getcwd() {
-    let tmp_dir = TempDir::new("test_getcwd").unwrap();
-    assert!(chdir(tmp_dir.path()).is_ok());
-    assert_eq!(getcwd().unwrap(), current_dir().unwrap());
-
-    // make path 500 chars longer so that buffer doubling in getcwd kicks in.
-    // Note: One path cannot be longer than 255 bytes (NAME_MAX)
-    // whole path cannot be longer than PATH_MAX (usually 4096 on linux, 1024 on macos)
-    let mut inner_tmp_dir = tmp_dir.path().to_path_buf();
-    for _ in 0..5 {
-        let newdir = iter::repeat("a").take(100).collect::<String>();
-        //inner_tmp_dir = inner_tmp_dir.join(newdir).path();
-        inner_tmp_dir.push(newdir);
-        assert!(mkdir(inner_tmp_dir.as_path(), stat::S_IRWXU).is_ok());
-    }
-    assert!(chdir(inner_tmp_dir.as_path()).is_ok());
-    assert_eq!(getcwd().unwrap(), current_dir().unwrap());
+    // chdir changes the process's cwd
+    test_in_subprocess(|| {
+        let tmp_dir = TempDir::new("test_getcwd").unwrap();
+        assert!(chdir(tmp_dir.path()).is_ok());
+        assert_eq!(getcwd().unwrap(), current_dir().unwrap());
+
+        // make path 500 chars longer so that buffer doubling in getcwd
+        // kicks in.  Note: One path cannot be longer than 255 bytes
+        // (NAME_MAX) whole path cannot be longer than PATH_MAX (usually
+        // 4096 on linux, 1024 on macos)
+        let mut inner_tmp_dir = tmp_dir.path().to_path_buf();
+        for _ in 0..5 {
+            let newdir = iter::repeat("a").take(100).collect::<String>();
+            //inner_tmp_dir = inner_tmp_dir.join(newdir).path();
+            inner_tmp_dir.push(newdir);
+            assert!(mkdir(inner_tmp_dir.as_path(), stat::S_IRWXU).is_ok());
+        }
+        assert!(chdir(inner_tmp_dir.as_path()).is_ok());
+        assert_eq!(getcwd().unwrap(), current_dir().unwrap());
+    });
 }
 
 #[test]