Merge pull request #688 from robotpy/keep-putdata

Keep a reference to Sendable objects when passed to SmartDashboard::putData

gen/SmartDashboard.yml

@@ -1,5 +1,8 @@
 ---
 
+extra_includes:
+- src/rpy/SmartDashboardData.h
+
 classes:
   SmartDashboard:
     nodelete: true
@@ -21,13 +24,38 @@ classes:
       Delete:
       GetEntry:
       PutData:
+        # overrides ensure data doesn't die if this is the only reference
         overloads:
           wpi::StringRef, Sendable*:
-            # keepalive:
-            # - [1, 3]
+            cpp_code: |
+              [](py::str &key, std::shared_ptr<Sendable> data) {
+
+                // convert key to a raw string so that we can create a StringRef
+                Py_ssize_t raw_size;
+                const char *raw_str = PyUnicode_AsUTF8AndSize(key.ptr(), &raw_size);
+                if (raw_str == NULL) {
+                  throw py::error_already_set();
+                }
+
+                wpi::StringRef keyRef(raw_str, raw_size);
+                frc::SmartDashboard::PutData(keyRef, data.get());
+
+                // this comes after the PutData to ensure that the original object doesn't die
+                // while PutData is called
+                rpy::addSmartDashboardData(key, data);
+              }
           Sendable*:
-            # keepalive:
-            #   - [1, 2]
+            cpp_code: |
+              [](std::shared_ptr<Sendable> value) {
+                frc::SmartDashboard::PutData(value.get());
+                // this comes after the PutData to ensure that the original object doesn't die
+                // while PutData is called
+                auto name = SendableRegistry::GetInstance().GetName(value.get());
+                if (!name.empty()) {
+                  py::str key(name);
+                  rpy::addSmartDashboardData(key, value);
+                }
+              }
       GetData:
       PutBoolean:
       SetDefaultBoolean:
@@ -139,3 +167,11 @@ classes:
       GetValue:
       PostListenerTask:
       UpdateValues:
+
+inline_code: |
+  // ensure that the smart dashboard data is released when python shuts down
+  static int unused; // the capsule needs something to reference
+  py::capsule cleanup(&unused, [](void *) {
+      rpy::clearSmartDashboardData();
+  });
+  m.add_object("_sd_cleanup", cleanup);

pyproject.toml

@@ -30,6 +30,7 @@ sources = [
     "wpilib/src/main.cpp",
     "wpilib/src/rpy/ControlWord.cpp",
     "wpilib/src/rpy/Notifier.cpp",
+    "wpilib/src/rpy/SmartDashboardData.cpp",
     "wpilib/src/rpy/SpeedControllerGroup.cpp",
 ]
 

tests/test_wpilib.py

@@ -1,4 +1,5 @@
 import wpilib
+import weakref
 
 
 def test_sendable_chooser():
@@ -7,3 +8,12 @@ def test_sendable_chooser():
 
     chooser.setDefaultOption("option", True)
     assert chooser.getSelected() is True
+
+
+def test_smart_dashboard_putdata():
+    t = wpilib.Talon(4)
+    ref = weakref.ref(t)
+    wpilib.SmartDashboard.putData("talon", t)
+    del t
+    assert bool(ref) is True
+    assert wpilib.SmartDashboard.getData("talon") is ref()

wpilib/src/rpy/SmartDashboardData.cpp

@@ -0,0 +1,33 @@
+
+#include "SmartDashboardData.h"
+
+namespace rpy {
+
+//
+// Ensures that python objects added to the SmartDashboard have at least one
+// reference to them
+//
+// All functions here must be called with the GIL held
+//
+
+static py::dict &getSmartDashboardData() {
+  static py::dict data;
+  return data;
+}
+
+void addSmartDashboardData(py::str &key, std::shared_ptr<frc::Sendable> data) {
+  auto &sdData = getSmartDashboardData();
+  sdData[key] = py::cast(data);
+}
+
+void clearSmartDashboardData() {
+  auto &sdData = getSmartDashboardData();
+  if (sdData) {
+    sdData.clear();
+    // force the dictionary to be deleted otherwise it'll crash when libc++
+    // is unwinding static objects after interpreter destruction
+    sdData.dec_ref();
+  }
+}
+
+} // namespace rpy

wpilib/src/rpy/SmartDashboardData.h

@@ -0,0 +1,16 @@
+
+#pragma once
+
+#include <frc/smartdashboard/Sendable.h>
+#include <robotpy_build.h>
+
+namespace rpy {
+
+//
+// These functions must be called with the GIL held
+//
+
+void addSmartDashboardData(py::str &key, std::shared_ptr<frc::Sendable> data);
+void clearSmartDashboardData();
+
+} // namespace rpy