Expose async transaction support in the C API (#5783)

* expose async transaction realm support in the C API

* changelog entry

* fix format checks

* code review

* appease format checks

* remove redundant realm parameter from callback

CHANGELOG.md

@@ -7,6 +7,7 @@
 * `NotificationToken` grew an `unregister()` method as an alternative to destroying it or doing `token = {};` ([PR #5776](https://github.com/realm/realm-core/pull/5776)).
 * Automatic handling backlinks for schema migrations where a class changes to being embedded. ([PR #5737](https://github.com/realm/realm-core/pull/5737)).
 * Expose `Obj::add_int()` in the CAPI. ([PR #5770](https://github.com/realm/realm-core/pull/5770)).
+* Expose `Realm::async_begin_transaction`, `Realm::async_commit_transaction`, `Realm::async_cancel_transaction` in the CAPI.([PR 5783 #](https://github.com/realm/realm-core/pull/5783)).
 
 ### Fixed
 * <How do the end-user experience this issue? what was the impact?> ([#????](https://github.com/realm/realm-core/issues/????), since v?.?.?)

src/realm.h

@@ -372,6 +372,8 @@ typedef void (*realm_on_object_change_func_t)(realm_userdata_t userdata, const r
 typedef void (*realm_on_collection_change_func_t)(realm_userdata_t userdata, const realm_collection_changes_t*);
 typedef void (*realm_on_realm_change_func_t)(realm_userdata_t userdata);
 typedef void (*realm_on_realm_refresh_func_t)(realm_userdata_t userdata);
+typedef void (*realm_async_begin_write_func_t)(realm_userdata_t userdata);
+typedef void (*realm_async_commit_func_t)(realm_userdata_t userdata, bool error, const char* desc);
 
 /**
  * Callback for realm schema changed notifications.
@@ -1065,6 +1067,25 @@ RLM_API bool realm_commit(realm_t*);
  */
 RLM_API bool realm_rollback(realm_t*);
 
+/**
+ * start a new write transaction asynchronously for the realm passed as argument.
+ */
+RLM_API unsigned int realm_async_begin_write(realm_t* realm, realm_async_begin_write_func_t,
+                                             realm_userdata_t userdata, realm_free_userdata_func_t userdata_free,
+                                             bool notify_only);
+
+/**
+ * commit a transaction asynchronously for the realm passed as argument.
+ */
+RLM_API unsigned int realm_async_commit(realm_t* realm, realm_async_commit_func_t, realm_userdata_t userdata,
+                                        realm_free_userdata_func_t userdata_free, bool allow_grouping);
+
+/**
+ * Cancel the transaction referenced by the token passed as argument and set the optional boolean flag in order to
+ * inform the caller if the transaction was cancelled.
+ */
+RLM_API bool realm_async_cancel(realm_t* realm, unsigned int token, bool* cancelled);
+
 /**
  * Add a callback that will be invoked every time the view of this file is updated.
  *
@@ -3730,7 +3751,6 @@ RLM_API uint64_t realm_async_open_task_register_download_progress_notifier(
     realm_free_userdata_func_t userdata_free) RLM_API_NOEXCEPT;
 RLM_API void realm_async_open_task_unregister_download_progress_notifier(realm_async_open_task_t*,
                                                                          uint64_t token) RLM_API_NOEXCEPT;
-
 /**
  * Get the sync session for a specific realm.
  *

src/realm/object-store/c_api/realm.cpp

@@ -16,7 +16,6 @@ realm_refresh_callback_token::~realm_refresh_callback_token()
     realm::c_api::CBindingContext::get(*m_realm).realm_pending_refresh_callbacks().remove(m_token);
 }
 
-
 namespace realm::c_api {
 
 
@@ -125,7 +124,7 @@ RLM_API bool realm_is_closed(realm_t* realm)
 
 RLM_API bool realm_is_writable(const realm_t* realm)
 {
-    return (*realm)->is_in_transaction();
+    return (*realm)->is_in_transaction() || (*realm)->is_in_async_transaction();
 }
 
 RLM_API bool realm_close(realm_t* realm)
@@ -168,6 +167,49 @@ RLM_API bool realm_rollback(realm_t* realm)
     });
 }
 
+RLM_API unsigned int realm_async_begin_write(realm_t* realm, realm_async_begin_write_func_t callback,
+                                             realm_userdata_t userdata, realm_free_userdata_func_t userdata_free,
+                                             bool notify_only)
+{
+    auto cb = [callback, userdata = UserdataPtr{userdata, userdata_free}]() {
+        callback(userdata.get());
+    };
+    return wrap_err([&]() {
+        return (*realm)->async_begin_transaction(std::move(cb), notify_only);
+    });
+}
+
+RLM_API unsigned int realm_async_commit(realm_t* realm, realm_async_commit_func_t callback, realm_userdata_t userdata,
+                                        realm_free_userdata_func_t userdata_free, bool allow_grouping)
+{
+    auto cb = [callback, userdata = UserdataPtr{userdata, userdata_free}](std::exception_ptr err) {
+        if (err) {
+            try {
+                std::rethrow_exception(err);
+            }
+            catch (const std::exception& e) {
+                callback(userdata.get(), true, e.what());
+            }
+        }
+        else {
+            callback(userdata.get(), false, nullptr);
+        }
+    };
+    return wrap_err([&]() {
+        return (*realm)->async_commit_transaction(std::move(cb), allow_grouping);
+    });
+}
+
+RLM_API bool realm_async_cancel(realm_t* realm, unsigned int token, bool* cancelled)
+{
+    return wrap_err([&]() {
+        auto res = (*realm)->async_cancel_transaction(token);
+        if (cancelled)
+            *cancelled = res;
+        return true;
+    });
+}
+
 RLM_API realm_callback_token_t* realm_add_realm_changed_callback(realm_t* realm,
                                                                  realm_on_realm_change_func_t callback,
                                                                  realm_userdata_t userdata,

test/object-store/c_api/c_api.cpp

@@ -1083,31 +1083,47 @@ TEST_CASE("C API", "[c_api]") {
     }
 
     SECTION("realm refresh async pending") {
-        bool realm_refresh_callback_called = false;
-        // bool on_transaction_completed = false;
-        bool done = false;
+        struct TestingObj {
+            static TestingObj& get()
+            {
+                static TestingObj obj;
+                return obj;
+            }
+            bool done{false};
+            bool realm_refresh_callback_called{false};
+            realm_t* realm{nullptr};
+        };
+
         auto wait_for_done = [&]() {
             util::EventLoop::main().run_until([&] {
-                return done;
+                return TestingObj::get().done;
             });
-            REQUIRE(done);
+            REQUIRE(TestingObj::get().done);
         };
-        (*realm)->async_begin_transaction([&]() {
-            auto token = cptr(realm_add_realm_refresh_callback(
-                realm,
-                [](void* userdata) {
-                    *reinterpret_cast<bool*>(userdata) = true;
-                },
-                &realm_refresh_callback_called, [](void*) {}));
-
-            (*realm)->async_commit_transaction([&](std::exception_ptr) {
-                done = true;
-            });
-        });
+        TestingObj::get().realm = realm;
 
+        realm_async_begin_write(
+            realm,
+            [](void*) {
+                auto realm = TestingObj::get().realm;
+                auto token_refresh = cptr(realm_add_realm_refresh_callback(
+                    realm,
+                    [](void* userdata) {
+                        *reinterpret_cast<bool*>(userdata) = true;
+                    },
+                    &(TestingObj::get().realm_refresh_callback_called), [](void*) {}));
+
+                realm_async_commit(
+                    realm,
+                    [](void*, bool, const char*) {
+                        TestingObj::get().done = true;
+                    },
+                    nullptr, nullptr, false);
+            },
+            nullptr, nullptr, false);
 
         wait_for_done();
-        CHECK(realm_refresh_callback_called);
+        CHECK(TestingObj::get().realm_refresh_callback_called);
     }
 
     SECTION("realm async refresh - main use case") {