SDK - Got rid of the global variable collecting all created pipelines (…

…#1167)

* SDK - Got rid of the global variable collecting all created pipelines
This list was only used by the command-line compiler.
The command-line compiler can still collect the created pipelines by registering a handler function in `_pipeline_decorator_handlers`.

* Replaced handler stack with a single handler.

sdk/python/kfp/compiler/main.py

@@ -51,9 +51,7 @@ def parse_arguments():
   return args
 
 
-def _compile_pipeline_function(function_name, output_path, type_check):
-
-  pipeline_funcs = dsl.Pipeline.get_pipeline_functions()
+def _compile_pipeline_function(pipeline_funcs, function_name, output_path, type_check):
   if len(pipeline_funcs) == 0:
     raise ValueError('A function with @dsl.pipeline decorator is required in the py file.')
 
@@ -72,13 +70,28 @@ def _compile_pipeline_function(function_name, output_path, type_check):
   kfp.compiler.Compiler().compile(pipeline_func, output_path, type_check)
 
 
+class PipelineCollectorContext():
+  def __enter__(self):
+    pipeline_funcs = []
+    def add_pipeline(func):
+      pipeline_funcs.append(func)
+      return func
+    self.old_handler = dsl._pipeline._pipeline_decorator_handler
+    dsl._pipeline._pipeline_decorator_handler = add_pipeline
+    return pipeline_funcs
+
+  def __exit__(self, *args):
+    dsl._pipeline._pipeline_decorator_handler = self.old_handler
+
+
 def compile_package(package_path, namespace, function_name, output_path, type_check):
   tmpdir = tempfile.mkdtemp()
   sys.path.insert(0, tmpdir)
   try:
     subprocess.check_call(['python3', '-m', 'pip', 'install', package_path, '-t', tmpdir])
-    __import__(namespace)
-    _compile_pipeline_function(function_name, output_path, type_check)
+    with PipelineCollectorContext() as pipeline_funcs:
+      __import__(namespace)
+    _compile_pipeline_function(pipeline_funcs, function_name, output_path, type_check)
   finally:
     del sys.path[0]
     shutil.rmtree(tmpdir)
@@ -88,8 +101,9 @@ def compile_pyfile(pyfile, function_name, output_path, type_check):
   sys.path.insert(0, os.path.dirname(pyfile))
   try:
     filename = os.path.basename(pyfile)
-    __import__(os.path.splitext(filename)[0])
-    _compile_pipeline_function(function_name, output_path, type_check)
+    with PipelineCollectorContext() as pipeline_funcs:
+      __import__(os.path.splitext(filename)[0])
+    _compile_pipeline_function(pipeline_funcs, function_name, output_path, type_check)
   finally:
     del sys.path[0]
 

sdk/python/kfp/dsl/_pipeline.py

@@ -19,6 +19,11 @@
 import sys
 
 
+# This handler is called whenever the @pipeline decorator is applied.
+# It can be used by command-line DSL compiler to inject code that runs for every pipeline definition.
+_pipeline_decorator_handler = None
+
+
 def pipeline(name, description):
   """Decorator of pipeline functions.
 
@@ -35,8 +40,11 @@ def my_pipeline(a: PipelineParam, b: PipelineParam):
   def _pipeline(func):
     func._pipeline_name = name
     func._pipeline_description = description
-    Pipeline._add_pipeline_to_global_list(func)
-    return func
+
+    if _pipeline_decorator_handler:
+      return _pipeline_decorator_handler(func) or func
+    else:
+      return func 
 
   return _pipeline
 
@@ -82,31 +90,16 @@ class Pipeline():
   # _default_pipeline is set when it (usually a compiler) runs "with Pipeline()"
   _default_pipeline = None
 
-  # All pipeline functions with @pipeline decorator that are imported.
-  # Each key is a pipeline function. Each value is a (name, description).
-  _pipeline_functions = []
-
   @staticmethod
   def get_default_pipeline():
     """Get default pipeline. """
     return Pipeline._default_pipeline
 
-  @staticmethod
-  def get_pipeline_functions():
-    """Get all imported pipeline functions (decorated with @pipeline)."""
-    return Pipeline._pipeline_functions
-
-  @staticmethod
-  def _add_pipeline_to_global_list(func):
-    """Add a pipeline function (decorated with @pipeline)."""
-    Pipeline._pipeline_functions.append(func)
-
   @staticmethod
   def add_pipeline(name, description, func):
     """Add a pipeline function with the specified name and description."""
     # Applying the @pipeline decorator to the pipeline function
     func = pipeline(name=name, description=description)(func)
-    Pipeline._add_pipeline_to_global_list(pipeline_meta, func)
 
   def __init__(self, name: str):
     """Create a new instance of Pipeline.