[hal] Add HAL_Shutdown and simulation shutdown callbacks

This is useful for clean shutdown of simulation extensions.

hal/src/main/native/athena/HAL.cpp

@@ -420,6 +420,8 @@ HAL_Bool HAL_Initialize(int32_t timeout, int32_t mode) {
   return true;
 }
 
+void HAL_Shutdown(void) {}
+
 int64_t HAL_Report(int32_t resource, int32_t instanceNumber, int32_t context,
                    const char* feature) {
   if (feature == nullptr) {

hal/src/main/native/cpp/jni/HAL.cpp

@@ -36,6 +36,18 @@ Java_edu_wpi_first_hal_HAL_initialize
   return HAL_Initialize(timeout, mode);
 }
 
+/*
+ * Class:     edu_wpi_first_hal_HAL
+ * Method:    shutdown
+ * Signature: ()V
+ */
+JNIEXPORT void JNICALL
+Java_edu_wpi_first_hal_HAL_shutdown
+  (JNIEnv*, jclass)
+{
+  return HAL_Shutdown();
+}
+
 /*
  * Class:     edu_wpi_first_hal_HAL
  * Method:    hasMain

hal/src/main/native/include/hal/Extensions.h

@@ -25,7 +25,10 @@
  */
 typedef int halsim_extension_init_func_t(void);
 
+#ifdef __cplusplus
 extern "C" {
+#endif
+
 /**
  * Loads a single extension from a direct path.
  *
@@ -82,5 +85,17 @@ void HAL_RegisterExtensionListener(void* param,
  * @param showMessage true to show message, false to not.
  */
 void HAL_SetShowExtensionsNotFoundMessages(HAL_Bool showMessage);
+
+/**
+ * Registers a function to be called from HAL_Shutdown(). This is intended
+ * for use only by simulation extensions.
+ *
+ * @param param parameter data to pass to callback function
+ * @param func callback function
+ */
+void HAL_OnShutdown(void* param, void (*func)(void*));
+
+#ifdef __cplusplus
 }  // extern "C"
+#endif
 /** @} */

hal/src/main/native/include/hal/HALBase.h

@@ -149,6 +149,14 @@ uint64_t HAL_ExpandFPGATime(uint32_t unexpanded_lower, int32_t* status);
  */
 HAL_Bool HAL_Initialize(int32_t timeout, int32_t mode);
 
+/**
+ * Call this to shut down HAL.
+ *
+ * This must be called at termination of the robot program to avoid potential
+ * segmentation faults with simulation extensions at exit.
+ */
+void HAL_Shutdown(void);
+
 #ifdef __cplusplus
 }  // extern "C"
 #endif

hal/src/main/native/sim/HAL.cpp

@@ -7,8 +7,11 @@
 
 #include "hal/HAL.h"
 
+#include <vector>
+
 #include <wpi/mutex.h>
 #include <wpi/raw_ostream.h>
+#include <wpi/spinlock.h>
 
 #ifdef _WIN32
 #include <Windows.h>
@@ -28,6 +31,8 @@
 using namespace hal;
 
 static HAL_RuntimeType runtimeType{HAL_Mock};
+static wpi::spinlock gOnShutdownMutex;
+static std::vector<std::pair<void*, void (*)(void*)>> gOnShutdown;
 
 namespace hal {
 namespace init {
@@ -312,6 +317,22 @@ HAL_Bool HAL_Initialize(int32_t timeout, int32_t mode) {
   return true;  // Add initialization if we need to at a later point
 }
 
+void HAL_Shutdown(void) {
+  std::vector<std::pair<void*, void (*)(void*)>> funcs;
+  {
+    std::scoped_lock lock(gOnShutdownMutex);
+    funcs.swap(gOnShutdown);
+  }
+  for (auto&& func : funcs) {
+    func.second(func.first);
+  }
+}
+
+void HAL_OnShutdown(void* param, void (*func)(void*)) {
+  std::scoped_lock lock(gOnShutdownMutex);
+  gOnShutdown.emplace_back(param, func);
+}
+
 int64_t HAL_Report(int32_t resource, int32_t instanceNumber, int32_t context,
                    const char* feature) {
   return 0;  // Do nothing for now