kernel: Add interrupt function to C header

Calling interrupt can halt long-running functions associated with
objects that were created through the passed-in context.

src/kernel/bitcoinkernel.cpp

@@ -676,6 +676,11 @@ btck_Context* btck_context_copy(const btck_Context* context)
     return btck_Context::copy(context);
 }
 
+int btck_context_interrupt(btck_Context* context)
+{
+    return (*btck_Context::get(context)->m_interrupt)() ? 0 : -1;
+}
+
 void btck_context_destroy(btck_Context* context)
 {
     delete context;

src/kernel/bitcoinkernel.h

@@ -704,6 +704,16 @@ BITCOINKERNEL_API btck_Context* BITCOINKERNEL_WARN_UNUSED_RESULT btck_context_cr
 BITCOINKERNEL_API btck_Context* BITCOINKERNEL_WARN_UNUSED_RESULT btck_context_copy(
     const btck_Context* context) BITCOINKERNEL_ARG_NONNULL(1);
 
+/**
+ * @brief Interrupt can be used to halt long-running validation functions like
+ * when reindexing, importing or processing blocks.
+ *
+ * @param[in] context  Non-null.
+ * @return             0 if the interrupt was successful, non-zero otherwise.
+ */
+BITCOINKERNEL_API int BITCOINKERNEL_WARN_UNUSED_RESULT btck_context_interrupt(
+    btck_Context* context) BITCOINKERNEL_ARG_NONNULL(1);
+
 /**
  * Destroy the context.
  */

src/kernel/bitcoinkernel_wrapper.h

@@ -651,6 +651,11 @@ public:
 
     Context()
         : Handle{btck_context_create(ContextOptions{}.get())} {}
+
+    bool interrupt()
+    {
+        return btck_context_interrupt(get()) == 0;
+    }
 };
 
 class ChainstateManagerOptions : public UniqueHandle<btck_ChainstateManagerOptions, btck_chainstate_manager_options_destroy>

src/test/kernel/test_kernel.cpp

@@ -634,6 +634,8 @@ BOOST_AUTO_TEST_CASE(btck_chainman_in_memory_tests)
     BOOST_CHECK(std::filesystem::exists(in_memory_test_directory.m_directory / "blocks"));
     BOOST_CHECK(!std::filesystem::exists(in_memory_test_directory.m_directory / "blocks" / "index"));
     BOOST_CHECK(!std::filesystem::exists(in_memory_test_directory.m_directory / "chainstate"));
+
+    BOOST_CHECK(context.interrupt());
 }
 
 BOOST_AUTO_TEST_CASE(btck_chainman_regtest_tests)