sync: add `pub sync.thread_id() u64 {` API

vlib/sync/sync_darwin.c.v

@@ -10,6 +10,7 @@ import time
 #include <sys/errno.h>
 
 [trusted]
+fn C.pthread_self() usize
 fn C.pthread_mutex_init(voidptr, voidptr) int
 fn C.pthread_mutex_lock(voidptr) int
 fn C.pthread_mutex_unlock(voidptr) int

vlib/sync/sync_default.c.v

@@ -14,6 +14,7 @@ $if !android {
 #include <semaphore.h>
 
 [trusted]
+fn C.pthread_self() usize
 fn C.pthread_mutex_init(voidptr, voidptr) int
 fn C.pthread_mutex_lock(voidptr) int
 fn C.pthread_mutex_unlock(voidptr) int

vlib/sync/sync_windows.c.v

@@ -8,6 +8,7 @@ import time
 #include <synchapi.h>
 #include <time.h>
 
+fn C.GetCurrentThreadId() u32
 fn C.GetSystemTimeAsFileTime(lpSystemTimeAsFileTime &C._FILETIME)
 fn C.InitializeConditionVariable(voidptr)
 fn C.WakeConditionVariable(voidptr)

vlib/sync/thread.c.v

@@ -0,0 +1,9 @@
+module sync
+
+pub fn thread_id() u64 {
+	$if windows {
+		return u64(C.GetCurrentThreadId())
+	} $else {
+		return u64(C.pthread_self())
+	}
+}

vlib/sync/thread_test.v

@@ -0,0 +1,22 @@
+import sync
+
+fn simple_thread() u64 {
+	tid := sync.thread_id()
+	eprintln('simple_thread thread_id: $tid.hex()')
+	return tid
+}
+
+fn test_sync_thread_id() {
+	mtid := sync.thread_id()
+	eprintln('main thread_id: $sync.thread_id().hex()')
+	x := go simple_thread()
+	y := go simple_thread()
+	xtid := x.wait()
+	ytid := y.wait()
+	eprintln('main thread_id: $sync.thread_id().hex()')
+	dump(xtid.hex())
+	dump(ytid.hex())
+	assert mtid != xtid
+	assert mtid != ytid
+	assert xtid != ytid
+}