std-thread-current-pass.patch

diff --git a/src/thread/lib_pthread.cr b/src/thread/lib_pthread.cr
index 5094260..96f2530 100644
--- a/src/thread/lib_pthread.cr
+++ b/src/thread/lib_pthread.cr
@@ -17,6 +17,7 @@ lib LibPThread
 
   fun create = pthread_create(thread : Thread*, attr : Void*, start : Void* ->, arg : Void*) : Int32
   fun exit = pthread_exit(value : Void*)
+  fun yield = pthread_yield() : Int32
   fun join = pthread_join(thread : Thread, value : Void**) : Int32
 
   fun mutex_init = pthread_mutex_init(mutex : Mutex*, mutex_attr : MutexAttr) : Int32
diff --git a/src/thread/thread.cr b/src/thread/thread.cr
index b10d57d..e024ece 100644
--- a/src/thread/thread.cr
+++ b/src/thread/thread.cr
@@ -1,6 +1,21 @@
 require "./*"
 
 class Thread(T, R)
+  @[ThreadLocal]
+  $__crystal_current_thread = nil
+
+  def self.current
+    if thread = $__crystal_current_thread
+      thread
+    else
+      raise "Could not get current thread"
+    end
+  end
+
+  def self.pass
+    LibPThread.yield
+  end
+
   def self.new(&func : -> R)
     Thread(Nil, R).new(nil) { func.call }
   end
@@ -8,19 +23,17 @@ class Thread(T, R)
   def initialize(arg : T, &func : T -> R)
     @func = func
     @arg = arg
-    ret = LibPThread.create(out @th, nil, ->(data) {
-        (data as Thread(T, R)).start
+
+    success = LibPThread.create(out @th, nil, ->(data) {
+        ($__crystal_current_thread = data as Thread(T, R)).start
       }, self as Void*)
 
-    if ret != 0
-      raise Errno.new("pthread_create")
-    end
+    raise Errno.new("pthread_create") if success != 0
   end
 
   def join
-    if LibPThread.join(@th, out _ret) != 0
-      raise Errno.new("pthread_join")
-    end
+    success = LibPThread.join(@th, out _ret)
+    raise Errno.new("pthread_join") if success != 0
 
     if exception = @exception
       raise exception
@@ -44,6 +57,8 @@ class Thread(T, R)
       @ret = @func.call(@arg)
     rescue ex
       @exception = ex
+    ensure
+      $__crystal_current_thread = nil
     end
   end
 end