Dynamically Linked Library in CPP #11439

soumiiow · 2024-11-05T13:11:52Z

Related to prestodb/presto#23634 in the Prestissimo space
and based off of the following PR: https://github.com/facebookincubator/velox/pull/1005/files

These changes will allow users to dynamically load functions in prestissimo using cpp. The Presto Server will use this library to dynamically load User Defined Functions (UDFs), connectors, or types.

an example of dynamically registering a function is also provided for reference, along with a unit test

Currently, this library works on linux machines but not MacOS.

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pedroerp · 2024-11-05T15:50:57Z

@soumiiow thanks for looking into this. Out of curiosity, why doesn't this work in MacOS?

pedroerp · 2024-11-05T15:52:59Z

velox/common/CMakeLists.txt

@@ -15,6 +15,7 @@ add_subdirectory(base)
 add_subdirectory(caching)
 add_subdirectory(compression)
 add_subdirectory(config)
+add_subdirectory(dynamicRegistry)


we use snake case for directory names "dynamic_registry"

pedroerp

Very cool! I few small comments but overall looks good.

pedroerp · 2024-11-05T15:53:27Z

velox/common/dynamicRegistry/DynamicLibraryLoader.cpp

+#include <dlfcn.h>
+#include <iostream>
+#include "velox/common/base/Exceptions.h"
+namespace facebook::velox {


nit: new line before namespace definition.

pedroerp · 2024-11-05T15:55:15Z

velox/common/dynamicRegistry/DynamicLibraryLoader.cpp

+    VELOX_USER_FAIL("Couldn't find Velox registry symbol: {}", error);
+  }
+  registryItem();
+  std::cout << "LOADED DYLLIB 1" << std::endl;


for consistency, could you use LOG(INFO) and print the file name / path of the library loaded?

pedroerp · 2024-11-05T15:56:10Z

velox/common/dynamicRegistry/DynamicLibraryLoader.cpp

+
+static constexpr const char* kSymbolName = "registry";
+
+void loadDynamicLibraryFunctions(const char* fileName) {


we can probably omit the "Functions" from the name, and this can be used to really load anything, as long as you provide the registration functions. Let's name it loadDynamicLibrary()

pedroerp · 2024-11-05T15:57:02Z

velox/common/dynamicRegistry/README.md

+### 1. Create a cpp file for your dynamic library
+For dynamically loaded function registration, the format followed is mirrored of that of built-in function registration with some noted differences. Using [MyDynamicTestFunction.cpp](tests/MyDynamicTestFunction.cpp) as an example, the function uses the extern "C" keyword to protect against name mangling. A registry() function call is also necessary here.
+
+### 2. Register functions dynamically by creating .dylib or .so shared libraries and dropping them in a plugin directory


nit: the titles are too long; maybe just add the docs as a refular numbered list?

I pushed it out without the title formatting but does this look a bit cluttered now?

pedroerp · 2024-11-05T15:58:20Z

velox/common/dynamicRegistry/tests/DynamicLinkTest.cpp

+  auto signaturesBefore = getFunctionSignatures().size();
+
+  // Function does not exist yet.
+  EXPECT_THROW(dynamicFunction(0), VeloxUserError);


can you use VELOX_ASSERT_THROW() instead to validate the right exception is being thrown?

pedroerp · 2024-11-05T15:59:22Z

velox/common/dynamicRegistry/tests/CMakeLists.txt

+# `MyDynamicFunction.cpp` as a small .so library, and use the
+# MY_DYNAMIC_FUNCTION_LIBRARY_PATH macro to locate the .so binary.
+add_compile_definitions(
+  MY_DYNAMIC_FUNCTION_LIBRARY_PATH="${CMAKE_CURRENT_BINARY_DIR}")


please vendor the macro. Maybe something like VELOX_TEST_DYNAMIC_LIBRARY_PATH

majetideepak · 2024-11-05T17:57:06Z

velox/common/dynamicRegistry/DynamicLibraryLoader.cpp

+ * limitations under the License.
+ */
+
+#include "velox/common/dynamicRegistry/DynamicLibraryLoader.h"


this header include is not required.

majetideepak · 2024-11-05T18:02:38Z

velox/common/dynamicRegistry/tests/DynamicLinkTest.cpp

+
+  // Dynamically load the library.
+  std::string libraryPath = MY_DYNAMIC_FUNCTION_LIBRARY_PATH;
+  libraryPath += "/libvelox_function_my_dynamic.so";


Use CMAKE_SHARED_LIBRARY_SUFFIX and CMAKE_SHARED_LIBRARY_PREFIX to support MacOS.

https://stackoverflow.com/questions/32445070/how-does-cmake-know-which-prefixes-and-suffixes-to-add-to-shared-libraries
https://cmake.org/cmake/help/v3.0/variable/CMAKE_SHARED_LIBRARY_PREFIX.html
https://cmake.org/cmake/help/v3.0/variable/CMAKE_SHARED_LIBRARY_SUFFIX.html

What else is an issue for MacOS?

assignUser · 2024-11-12T19:54:41Z

velox/common/dynamic_registry/tests/CMakeLists.txt

+  ${GMock}
+  ${GTEST_BOTH_LIBRARIES})


please use the GTest:: targets

assignUser · 2024-11-12T19:56:46Z

velox/common/dynamic_registry/tests/CMakeLists.txt

+# To test functions being added by dynamically linked libraries, we compile
+# `MyDynamicFunction.cpp` as a small .so library, and use the
+# VELOX_TEST_DYNAMIC_LIBRARY_PATH macro to locate the .so binary.
+add_compile_definitions(


Please use target_compile_definitions( on the relevant target instead.

assignUser · 2024-11-12T19:58:15Z

velox/common/dynamic_registry/CMakeLists.txt

+if(${VELOX_BUILD_TESTING})
+  add_subdirectory(tests)
+endif()
+velox_add_library(velox_dynamic_function_loader DynamicLibraryLoader.cpp)


Suggested change

velox_add_library(velox_dynamic_function_loader DynamicLibraryLoader.cpp)

velox_add_library(velox_dynamic_function_loader DynamicLibraryLoader.cpp)

velox_link_libraries(velox_dynamic_function_loader PRIVATE velox_exception)

assignUser · 2024-11-12T19:59:38Z

velox/common/dynamic_registry/README.md

Thanks for adding docs!

majetideepak · 2024-11-12T19:57:00Z

velox/common/dynamic_registry/tests/CMakeLists.txt

+# VELOX_TEST_DYNAMIC_LIBRARY_PATH macro to locate the .so binary.
+add_compile_definitions(
+  VELOX_TEST_DYNAMIC_LIBRARY_PATH="${CMAKE_CURRENT_BINARY_DIR}")
+add_library(velox_function_my_dynamic SHARED MyDynamicFunction.cpp)


Add a new line before and after.

majetideepak · 2024-11-12T19:59:51Z

velox/common/dynamic_registry/tests/CMakeLists.txt

+# `MyDynamicFunction.cpp` as a small .so library, and use the
+# VELOX_TEST_DYNAMIC_LIBRARY_PATH macro to locate the .so binary.
+add_compile_definitions(
+  VELOX_TEST_DYNAMIC_LIBRARY_PATH="${CMAKE_CURRENT_BINARY_DIR}")


MacOS support is still missing. You can create the full library path here based on the CMake options I shared earlier.

majetideepak · 2024-11-12T20:00:38Z

velox/common/dynamic_registry/tests/MyDynamicFunction.cpp

@@ -0,0 +1,30 @@
+#include "velox/functions/Udf.h"


Missing license header here.

majetideepak · 2024-11-12T20:02:07Z

velox/common/dynamic_registry/README.md

@@ -0,0 +1,22 @@
+# Velox: Dynamically Loading Registry Libraries in C++


"Dynamic Loading of Velox Extensions" is probably a better title.

majetideepak · 2024-11-12T20:03:01Z

velox/common/dynamic_registry/README.md

@@ -0,0 +1,22 @@
+# Velox: Dynamically Loading Registry Libraries in C++
+
+This library adds the ability to load User Defined Functions (UDFs), connectors, or types without having to fork and build Prestissimo, through the use of shared libraries that a Prestissimo worker can access. These are to be loaded on launch of the Presto server. The Presto server searches for any .so or .dylib files and loads them using this library.


Prestissimo -> Velox. Remaining paragraph as well.

majetideepak · 2024-11-12T20:04:24Z

velox/common/dynamic_registry/README.md

+target_link_libraries(name_of_dynamic_fn PRIVATE xsimd fmt::fmt velox_expression)
+```
+
+3. In the Prestissimo worker's config.properties file, set the plugin.dir property


Move this to Prestissimo.

majetideepak · 2024-11-12T20:04:33Z

velox/common/dynamic_registry/README.md

+```
+plugin.dir="User\Test\Path\plugin"
+```
+4. When the worker or the sidecar process starts, it will scan the plugin directory and attempt to dynamically load all shared libraries


Move this to Prestissimo.

majetideepak · 2024-11-12T20:05:33Z

velox/common/dynamic_registry/DynamicLibraryLoader.h

+
+namespace facebook::velox {
+
+/// Dynamically opens and registers functions defined in a shared library (.so)


Remove (.so)
Add fullstop.

majetideepak · 2024-11-12T20:07:50Z

velox/common/dynamic_registry/DynamicLibraryLoader.h

+
+/// Dynamically opens and registers functions defined in a shared library (.so)
+///
+/// Given a shared library name (.so), this function will open it using dlopen,


Opens a shared library using dlopen, looks for the symbol registry, and invokes it.

majetideepak · 2024-11-12T20:10:07Z

velox/common/dynamic_registry/DynamicLibraryLoader.cpp

+
+  // Lookup the symbol.
+  void* registrySymbol = dlsym(handler, kSymbolName);
+  auto registryItem = reinterpret_cast<void (*)()>(registrySymbol);


How do we ensure the signature is void registry();? What happens if the return type is different or there are arguments?

aditi-pandit

Thanks @soumiiow. Had bunch of minor comments, except for a bigger one around testing.

aditi-pandit · 2024-11-13T05:04:56Z

velox/common/dynamic_registry/CMakeLists.txt

@@ -0,0 +1,4 @@
+if(${VELOX_BUILD_TESTING})


Nit : Don't think its a convention, but most CMakeLists files have the velox_add_library function calls before the sub-directory related functions/macros.

aditi-pandit · 2024-11-13T05:35:23Z

velox/common/dynamic_registry/DynamicLibraryLoader.cpp

+
+  // Lookup the symbol.
+  void* registrySymbol = dlsym(handler, kSymbolName);
+  auto registryItem = reinterpret_cast<void (*)()>(registrySymbol);


Nit : rename registryFunction

hey!! so i got some previous feedback to stay away from the "registryFunction" in the naming so as to not make it seem like this library is to be used exclusively for functions, and to move away from our initial design which was made with only the function loading in mind. Perhaps, would there be a better name for this variable than the work "item"? I can only rlly think of registryItem or registryPtr but would love to hear your suggestions too

@soumiiow : To me this is almost like the "main" function in a executable program. How about "loadLibrary" or "loadUserLibrary" or "enterUserLibrary" ? There could be code beyond registration here as well.

aditi-pandit · 2024-11-13T05:36:07Z

velox/common/dynamic_registry/DynamicLibraryLoader.cpp

+  if (error != nullptr) {
+    VELOX_USER_FAIL("Couldn't find Velox registry symbol: {}", error);
+  }
+  registryItem();


Add a comment "Invoke the registry function"

aditi-pandit · 2024-11-13T05:47:30Z

velox/common/dynamic_registry/tests/MyDynamicFunction.cpp

+
+void registry() {
+  facebook::velox::registerFunction<
+      facebook::velox::common::dynamicRegistry::Dynamic123Function,


This assumes that certain types/functions are already available at this point. Those types and functions depend on the registrations that the service like Prestissimo have done apriori before the "registry" function here is invoked. For this test, since its inherited from FunctionTestBase, all the Velox registrations are available.

So in general, this function assumes some context setup done already. It might be better to explicitly describe those assumptions here.

Or then change the test to not assume anything and do all the registrations within its code itself.

aditi-pandit · 2024-11-13T05:51:11Z

velox/common/dynamic_registry/tests/DynamicLinkTest.cpp

+  std::string libraryPath = VELOX_TEST_DYNAMIC_LIBRARY_PATH;
+  libraryPath += "/libvelox_function_my_dynamic.so";
+
+  loadDynamicLibrary(libraryPath.data());


Lets add some more test cases :
i) One that loads 2 different libraries and checks that the number of function signatures increment at each point.
ii) One that loads the same library again and validates the behavior. We are not likely to load the same library again in the service, but then its better to make that assumption explicit. But in any case its possible that you have 2 libraries that do the exact same thing that are loaded one after another. So then we should be explicit about the behavior then.
iii) An error case with an incorrect implementation of the
/ registry function signature.
iv) Generally when adding functions, we want to add them to a catalog, so they have a namespace. Prestissimo definitely has namespaces. How do you incorporate this in the logic ? It would be good for your test to demo a function added to a non-default namespace.

aditi-pandit · 2024-11-13T05:55:58Z

velox/common/dynamic_registry/tests/MyDynamicFunction.cpp

@@ -0,0 +1,30 @@
+#include "velox/functions/Udf.h"


Why does this file not have the copyright header ? Is it intentional so that we ensure we didn't trigger the build rules for it ?

BTW, our clients might use any copyright header they want. So we should ensure our builds can handle that.

aditi-pandit · 2024-11-13T05:58:52Z

velox/common/dynamic_registry/tests/MyDynamicFunction.cpp

+
+extern "C" {
+
+void registry() {


Do we need the entire function definition in the extern or is it possible to just declare the function here and have the definition elsewhere. Just asking as its possible the registration is big function or we want it to call other functions.

e.g. In this folder we have a bunch of window functions we want to expose for users to register. Might be better to use this kind of file structure as its more realistic : https://github.com/facebookincubator/velox/blob/main/velox/functions/prestosql/window/WindowFunctionsRegistration.cpp#L30

aditi-pandit · 2024-11-13T06:07:54Z

velox/common/dynamic_registry/README.md

+target_link_libraries(name_of_dynamic_fn PRIVATE xsimd fmt::fmt velox_expression)
+```
+
+3. In the Prestissimo worker's config.properties file, set the plugin.dir property


This is not relevant in Velox. And also since its not used anywhere in the current code, its hard to put this in picture.

aditi-pandit · 2024-11-13T06:18:03Z

velox/common/dynamic_registry/README.md

@@ -0,0 +1,22 @@
+# Velox: Dynamically Loading Registry Libraries in C++
+
+This library adds the ability to load User Defined Functions (UDFs), connectors, or types without having to fork and build Prestissimo, through the use of shared libraries that a Prestissimo worker can access. These are to be loaded on launch of the Presto server. The Presto server searches for any .so or .dylib files and loads them using this library.


It might be good to not talk about Prestissimo in this README.

This is a generic utility for dynamically loading a "registry" function from a library. Its sufficient to just say that this is for "Extensibility" features that add custom user code which could include new Velox types, functions, operators and connectors.

soumiiow requested a review from majetideepak as a code owner November 5, 2024 13:11

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soumiiow force-pushed the velox-dylib branch from 789da39 to c5cbea2 Compare November 12, 2024 15:42

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soumiiow force-pushed the velox-dylib branch from c5cbea2 to f8afbc0 Compare November 12, 2024 15:51

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soumiiow force-pushed the velox-dylib branch from f8afbc0 to 45cf7af Compare December 3, 2024 23:21

dylib functionality + test + readme with updates from reviews

4e82b71

soumiiow force-pushed the velox-dylib branch from 45cf7af to 4e82b71 Compare December 4, 2024 07:04


		static constexpr const char* kSymbolName = "registry";

		void loadDynamicLibraryFunctions(const char* fileName) {

	velox_add_library(velox_dynamic_function_loader DynamicLibraryLoader.cpp)
	velox_add_library(velox_dynamic_function_loader DynamicLibraryLoader.cpp)
	velox_link_libraries(velox_dynamic_function_loader PRIVATE velox_exception)

		@@ -0,0 +1,22 @@
		# Velox: Dynamically Loading Registry Libraries in C++

		@@ -0,0 +1,22 @@
		# Velox: Dynamically Loading Registry Libraries in C++

		This library adds the ability to load User Defined Functions (UDFs), connectors, or types without having to fork and build Prestissimo, through the use of shared libraries that a Prestissimo worker can access. These are to be loaded on launch of the Presto server. The Presto server searches for any .so or .dylib files and loads them using this library.


		namespace facebook::velox {

		/// Dynamically opens and registers functions defined in a shared library (.so)

Dynamically Linked Library in CPP #11439

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Dynamically Linked Library in CPP #11439

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soumiiow commented Nov 5, 2024

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