[Lldb-commits] [PATCH] D153735: [lldb][LocateModuleCallback] Implement API, Python interface

[Kazuki Sakamoto via Phabricator via lldb-commits]

splhack added a comment.

@clayborg yes, it'd be possible to pass the baton down to Platform.h since it is just `void *`, so no dependencies required.

But, first, let me explain the callback and baton flow.

----

For Python, user will set a callable Python object as the callback.
For C++ API, user will set a function pointer with a baton as the callback.

Both Python callback and C++ API callback will go into SBPlatform SetLocateModuleCallback.
SetLocateModuleCallback will use a lambda in order to convert ModuleSpec and FileSpec to SBModuleSpec and SBFileSpec.
This is because Platform.h and Target.cpp are not able to use SBModuleSpec and SBFileSpec.

  |               |                                      |                   |                                 |          |
  | user callback |<-----(SBModuleSpec, SBFileSpec)----->| SBPlatform lambda |<-----(ModuleSpec, FileSpec)---->| Platform |
  |      baton    |                                      |  captures callback|                                 |          |
  |               |                                      |           baton   |                                 |          |

This summary is what things are retained by which layer.

- Python
  - the user callable object
- SBPlatform
  - C++ API: the user callback and the baton
  - Python: LLDBSwigPythonCallLocateModuleCallback and the user callable object as a baton
- Platform
  - SBPlatform lambda in std::function

There are three things.

- SBPlatform lambda created by SetLocateModuleCallback, the type is Platform::LocateModuleCallback.
- The user callback or LLDBSwigPythonCallLocateModuleCallback, the type is SBPlatformLocateModuleCallback.
- The baton (for Python, this is the callable object)

----

And back to 'passing the baton down to Platform.h'.
As the locate callback implementation in D153734 <https://reviews.llvm.org/D153734> lldb/unittests/Target/LocateModuleCallbackTest.cpp,
internal users can use lambda to capture/retain anything for the callback. For example, `this` is captured by the locate callback in this case.
Therefore, no need to pass the baton down to Platform.h.

  m_platform_sp->SetLocateModuleCallback([this](const ModuleSpec &module_spec,
                                                FileSpec &module_file_spec,
                                                FileSpec &symbol_file_spec) {
    CheckCallbackArgs(module_spec, module_file_spec, symbol_file_spec);
    symbol_file_spec.SetPath(GetInputFilePath(k_breakpad_symbol_file));
    return Status();
  });




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  https://reviews.llvm.org/D153735/new/

https://reviews.llvm.org/D153735