support gettid on macos

Author: king6cong

src/unistd.rs

@@ -165,7 +165,7 @@ pub fn getpgrp() -> pid_t {
 /// Get the caller's thread ID (see
 /// [gettid(2)](http://man7.org/linux/man-pages/man2/gettid.2.html).
 ///
-/// This function is only available on Linux based systems.  In a single
+/// This implementation is only available on Linux based systems.  In a single
 /// threaded process, the main thread will have the same ID as the process.  In
 /// a multithreaded process, each thread will have a unique thread id but the
 /// same process ID.
@@ -178,6 +178,15 @@ pub fn gettid() -> pid_t {
     unsafe { libc::syscall(libc::SYS_gettid) as pid_t }
 }
 
+/// Get the caller's thread ID
+/// This is the macos implementation
+#[cfg(target_os = "macos")]
+#[inline]
+pub fn gettid() -> pid_t {
+    unsafe { libc::pthread_self() as pid_t }
+}
+
+
 /// Create a copy of the specified file descriptor (see
 /// [dup(2)](http://man7.org/linux/man-pages/man2/dup.2.html)).
 ///
@@ -272,7 +281,7 @@ pub fn fchdir(dirfd: RawFd) -> Result<()> {
 /// - the path already exists
 /// - the path name is too long (longer than `PATH_MAX`, usually 4096 on linux, 1024 on OS X)
 ///
-/// For a full list consult 
+/// For a full list consult
 /// [man mkdir(2)](http://man7.org/linux/man-pages/man2/mkdir.2.html#ERRORS)
 ///
 /// # Example