v1.4.4

source/core/StarRpcPromise.hpp

@@ -0,0 +1,175 @@
+#ifndef STAR_RPC_PROMISE_HPP
+#define STAR_RPC_PROMISE_HPP
+
+#include "StarEither.hpp"
+#include "StarString.hpp"
+
+namespace Star {
+
+STAR_EXCEPTION(RpcPromiseException, StarException);
+
+// The other side of an RpcPromise, can be used to either fulfill or fail a
+// paired promise.  Call either fulfill or fail function exactly once, any
+// further invocations will result in an exception.
+template <typename Result, typename Error = String>
+class RpcPromiseKeeper {
+public:
+  void fulfill(Result result);
+  void fail(Error error);
+
+private:
+  template <typename ResultT, typename ErrorT>
+  friend class RpcPromise;
+
+  function<void(Result)> m_fulfill;
+  function<void(Error)> m_fail;
+};
+
+// A generic promise for the result of a remote procedure call.  It has
+// reference semantics and is implicitly shared, but is not thread safe.
+template <typename Result, typename Error = String>
+class RpcPromise {
+public:
+  static pair<RpcPromise, RpcPromiseKeeper<Result, Error>> createPair();
+  static RpcPromise createFulfilled(Result result);
+  static RpcPromise createFailed(Error error);
+
+  // Has the respoonse either failed or succeeded?
+  bool finished() const;
+  // Has the response finished with success?
+  bool succeeded() const;
+  // Has the response finished with failure?
+  bool failed() const;
+
+  // Returns the result of the rpc call on success, nothing on failure or when
+  // not yet finished.
+  Maybe<Result> const& result() const;
+
+  // Returns the error of a failed rpc call.  Returns nothing if the call is
+  // successful or not yet finished.
+  Maybe<Error> const& error() const;
+
+  // Wrap this RpcPromise into another promise which returns instead the result
+  // of this function when fulfilled
+  template <typename Function>
+  decltype(auto) wrap(Function function);
+
+private:
+  template <typename ResultT, typename ErrorT>
+  friend class RpcPromise;
+
+  struct Value {
+    Maybe<Result> result;
+    Maybe<Error> error;
+  };
+
+  RpcPromise() = default;
+
+  function<Value const*()> m_getValue;
+};
+
+template <typename Result, typename Error>
+void RpcPromiseKeeper<Result, Error>::fulfill(Result result) {
+  m_fulfill(move(result));
+}
+
+template <typename Result, typename Error>
+void RpcPromiseKeeper<Result, Error>::fail(Error error) {
+  m_fail(move(error));
+}
+
+template <typename Result, typename Error>
+pair<RpcPromise<Result, Error>, RpcPromiseKeeper<Result, Error>> RpcPromise<Result, Error>::createPair() {
+  auto valuePtr = make_shared<Value>();
+
+  RpcPromise promise;
+  promise.m_getValue = [valuePtr]() {
+    return valuePtr.get();
+  };
+
+  RpcPromiseKeeper<Result, Error> keeper;
+  keeper.m_fulfill = [valuePtr](Result result) {
+    if (valuePtr->result || valuePtr->error)
+      throw RpcPromiseException("fulfill called on already finished RpcPromise");
+    valuePtr->result = move(result);
+  };
+  keeper.m_fail = [valuePtr](Error error) {
+    if (valuePtr->result || valuePtr->error)
+      throw RpcPromiseException("fail called on already finished RpcPromise");
+    valuePtr->error = move(error);
+  };
+
+  return {move(promise), move(keeper)};
+}
+
+template <typename Result, typename Error>
+RpcPromise<Result, Error> RpcPromise<Result, Error>::createFulfilled(Result result) {
+  auto valuePtr = make_shared<Value>();
+  valuePtr->result = move(result);
+
+  RpcPromise<Result, Error> promise;
+  promise.m_getValue = [valuePtr]() {
+    return valuePtr.get();
+  };
+  return promise;
+}
+
+template <typename Result, typename Error>
+RpcPromise<Result, Error> RpcPromise<Result, Error>::createFailed(Error error) {
+  auto valuePtr = make_shared<Value>();
+  valuePtr->error = move(error);
+
+  RpcPromise<Result, Error> promise;
+  promise.m_getValue = [valuePtr]() {
+    return valuePtr.get();
+  };
+  return promise;
+}
+
+template <typename Result, typename Error>
+bool RpcPromise<Result, Error>::finished() const {
+  auto val = m_getValue();
+  return val->result || val->error;
+}
+
+template <typename Result, typename Error>
+bool RpcPromise<Result, Error>::succeeded() const {
+  return m_getValue()->result.isValid();
+}
+
+template <typename Result, typename Error>
+bool RpcPromise<Result, Error>::failed() const {
+  return m_getValue()->error.isValid();
+}
+
+template <typename Result, typename Error>
+Maybe<Result> const& RpcPromise<Result, Error>::result() const {
+  return m_getValue()->result;
+}
+
+template <typename Result, typename Error>
+Maybe<Error> const& RpcPromise<Result, Error>::error() const {
+  return m_getValue()->error;
+}
+
+template <typename Result, typename Error>
+template <typename Function>
+decltype(auto) RpcPromise<Result, Error>::wrap(Function function) {
+  typedef RpcPromise<typename std::decay<decltype(function(std::declval<Result>()))>::type, Error> WrappedPromise;
+  WrappedPromise wrappedPromise;
+  wrappedPromise.m_getValue = [wrapper = move(function), valuePtr = make_shared<typename WrappedPromise::Value>(), otherGetValue = m_getValue]() {
+    if (!valuePtr->result && !valuePtr->error) {
+      auto otherValue = otherGetValue();
+      if (otherValue->result)
+        valuePtr->result.set(wrapper(*otherValue->result));
+      else if (otherValue->error)
+        valuePtr->error.set(*otherValue->error);
+    }
+    return valuePtr.get();
+  };
+  return wrappedPromise;
+}
+
+}
+
+#endif