[Core][Feature] Add cross thread propagation (#62)

README.md

@@ -86,7 +86,7 @@ with context.new_local_span(op='https://github.com/apache') as span:
 from time import sleep
 
 from skywalking import Component
-from skywalking.decorators import trace
+from skywalking.decorators import trace, runnable
 from skywalking.trace.context import SpanContext, get_context
 
 @trace()  # the operation name is the method name('some_other_method') by default
@@ -99,6 +99,15 @@ def some_method():
     some_other_method()
 
 
+@runnable() # cross thread propagation
+def some_method(): 
+    some_other_method()
+
+from threading import Thread
+t = Thread(target=some_method)
+t.start()
+
+
 context: SpanContext = get_context()
 with context.new_entry_span(op=str('https://github.com/apache/skywalking')) as span:
     span.component = Component.Flask

skywalking/decorators.py

@@ -44,3 +44,30 @@ def trace(
         return wrapper
 
     return decorator
+
+
+def runnable(
+        op: str = None,
+        layer: Layer = Layer.Unknown,
+        component: Component = Component.Unknown,
+):
+    def decorator(func):
+        snapshot = get_context().capture()
+
+        @wraps(func)
+        def wrapper(*args, **kwargs):
+            _op = op or "Thread/"+func.__name__
+            context = get_context()
+            with context.new_local_span(op=_op) as span:
+                context.continued(snapshot)
+                span.layer = layer
+                span.component = component
+                try:
+                    func(*args, **kwargs)
+                except Exception:
+                    span.raised()
+                    raise
+
+        return wrapper
+
+    return decorator

tests/plugin/sw_flask/services/consumer.py

@@ -18,6 +18,7 @@
 import requests
 
 from skywalking import agent, config
+from skywalking.decorators import runnable
 
 if __name__ == '__main__':
     config.service_name = 'consumer'
@@ -34,17 +35,13 @@ if __name__ == '__main__':
         from skywalking.trace.context import get_context
         get_context().put_correlation("correlation", "correlation")
 
-        def post(snap):
-            with get_context().new_local_span("/test"):
-                get_context().continued(snap)
-                requests.post("http://provider:9091/users")
-
-        snapshot = get_context().capture()
+        @runnable(op="/test")
+        def post():
+            requests.post("http://provider:9091/users")
 
         from threading import Thread
-        t = Thread(target=post, args=(snapshot,))
+        t = Thread(target=post)
         t.start()
-        t.join()
 
         res = requests.post("http://provider:9091/users")