Use gettid for thread id on unix

examples/hello.rs

@@ -1,3 +1,5 @@
+use std::thread;
+
 use log::*;
 
 fn main() {
@@ -15,8 +17,22 @@ fn main() {
     // Use a custom target string that is used as tag
     info!(target: "custom", "hello custom target");
 
-    // Invoke a log from a submodule
-    hello_again::hello();
+    for _ in 0..3 {
+        thread::spawn(|| {
+            trace!("hello");
+            info!("helloHello");
+            warn!("hellohello");
+            error!("HELLOHELLO");
+
+            // Use a custom target string that is used as tag
+            info!(target: "custom", "hello custom target");
+
+            // Invoke a log from a submodule
+            hello_again::hello();
+        })
+        .join()
+        .expect("failed to join thread");
+    }
 }
 
 mod hello_again {

src/thread.rs

@@ -1,21 +1,30 @@
-#[cfg(unix)]
+#[cfg(any(target_os = "linux", target_os = "android"))]
 #[inline]
-pub fn id() -> usize {
+pub fn id() -> i32 {
     #[allow(clippy::unnecessary_cast)]
     unsafe {
-        libc::pthread_self() as usize
+        libc::gettid() as i32
+    }
+}
+
+#[cfg(target_os = "macos")]
+#[inline]
+pub fn id() -> i32 {
+    #[allow(clippy::unnecessary_cast)]
+    unsafe {
+        libc::pthread_self() as i32
     }
 }
 
 #[cfg(windows)]
 #[inline]
-pub fn id() -> usize {
-    unsafe { winapi::um::processthreadsapi::GetCurrentThreadId() as usize }
+pub fn id() -> i32 {
+    unsafe { winapi::um::processthreadsapi::GetCurrentThreadId() as i32 }
 }
 
 #[cfg(target_os = "redox")]
 #[inline]
-pub fn id() -> usize {
+pub fn id() -> i32 {
     // Each thread has a separate pid on Redox.
-    syscall::getpid().unwrap()
+    syscall::getpid().unwrap() as i32
 }