File indexing completed on 2024-05-12 04:41:21

 /*
     SPDX-FileCopyrightText: 2014-2015 Daniel Vrátil <dvratil@redhat.com>
     SPDX-FileCopyrightText: 2016 Daniel Vrátil <dvratil@kde.org>
     SPDX-FileCopyrightText: 2016 Christian Mollekopf <mollekopf@kolabsystems.com>
 
     SPDX-License-Identifier: LGPL-2.0-or-later
 */
 
 #ifndef KASYNC_H
 #define KASYNC_H
 
 #include "kasync_export.h"
 
 #include <functional>
 #include <type_traits>
 #include <cassert>
 
 #include <QVariant>
 
 #include "future.h"
 #include "debug.h"
 
 #include "continuations_p.h"
 #include "executor_p.h"
 
 class QObject;
 
 /**
  * @mainpage KAsync
  *
  * @brief API to help write async code.
  *
  * This API is based around jobs that take lambdas to execute asynchronous tasks.
  * Each async operation can take a continuation that can then be used to execute
  * further async operations. That way it is possible to build async chains of
  * operations that can be stored and executed later on. Jobs can be composed,
  * similarly to functions.
  *
  * Relations between the components:
  * * Job: API wrapper around Executors chain. Can be destroyed while still running,
  *        because the actual execution happens in the background
  * * Executor: Describes task to execute. Executors form a linked list matching the
  *        order in which they will be executed. The Executor chain is destroyed when
  *        the parent Job is destroyed. However if the Job is still running it is
  *        guaranteed that the Executor chain will not be destroyed until the execution
  *        is finished.
  * * Execution: The running execution of the task stored in Executor. Each call to
  *        Job::exec() instantiates new Execution chain, which makes it possible for
  *        the Job to be executed multiple times (even in parallel).
  * * Future: Representation of the result that is being calculated
  *
  *
  * TODO: Possibility to abort a job through future (perhaps optional?)
  * TODO: Support for timeout, specified during exec call, after which the error
  *       handler gets called with a defined errorCode.
  */
 
 
 namespace KAsync {
 
 template<typename PrevOut, typename Out, typename ... In>
 class Executor;
 
 class JobBase;
 
 template<typename Out, typename ... In>
 class Job;
 
 //@cond PRIVATE
 namespace Private {
 
 template<typename Out, typename ... In>
 Job<Out, In ...> startImpl(Private::ContinuationHolder<Out, In ...> &&helper)
 {
     static_assert(sizeof...(In) <= 1, "Only one or zero input parameters are allowed.");
     return Job<Out, In...>(QSharedPointer<Private::Executor<Out, In ...>>::create(
                 std::forward<Private::ContinuationHolder<Out, In...>>(helper), nullptr, Private::ExecutionFlag::GoodCase));
 }
 
 } // namespace Private
 //@endcond
 
 
 /**
  * @relates Job
  *
  * Start an asynchronous job sequence.
  *
  * start() is your starting point to build a chain of jobs to be executed
  * asynchronously.
  *
  * @param func A continuation to be executed.
  */
 
 ///Sync continuation without job: [] () -> T { ... }
 template<typename Out = void, typename ... In, typename F>
 auto start(F &&func) -> std::enable_if_t<!std::is_base_of<JobBase, decltype(func(std::declval<In>() ...))>::value,
                                          Job<decltype(func(std::declval<In>() ...)), In...>>
 {
     static_assert(sizeof...(In) <= 1, "Only one or zero input parameters are allowed.");
     return Private::startImpl<Out, In...>(Private::ContinuationHolder<Out, In ...>(SyncContinuation<Out, In ...>(std::forward<F>(func))));
 }
 
 ///continuation with job: [] () -> KAsync::Job<...> { ... }
 template<typename Out = void, typename ... In, typename F>
 auto start(F &&func) -> std::enable_if_t<std::is_base_of<JobBase, decltype(func(std::declval<In>() ...))>::value,
                                          Job<typename decltype(func(std::declval<In>() ...))::OutType, In...>>
 {
     static_assert(sizeof...(In) <= 1, "Only one or zero input parameters are allowed.");
     return Private::startImpl<Out, In...>(Private::ContinuationHolder<Out, In ...>(JobContinuation<Out, In...>(std::forward<F>(func))));
 }
 
 ///Handle continuation: [] (KAsync::Future<T>, ...) { ... }
 template<typename Out = void, typename ... In>
 auto start(AsyncContinuation<Out, In ...> &&func) -> Job<Out, In ...>
 {
     static_assert(sizeof...(In) <= 1, "Only one or zero input parameters are allowed.");
     return Private::startImpl<Out, In...>(Private::ContinuationHolder<Out, In ...>(std::forward<AsyncContinuation<Out, In ...>>(func)));
 }
 
 enum ControlFlowFlag {
     Break,
     Continue
 };
 
 /**
  * @relates Job
  *
  * Async while loop.
  *
  * Loop continues while body returns ControlFlowFlag::Continue.
  */
 KASYNC_EXPORT Job<void> doWhile(const Job<ControlFlowFlag> &body);
 
 /**
  * @relates Job
  *
  * Async while loop.
  *
  * Shorthand that takes a continuation.
  *
  * @see doWhile
  */
 KASYNC_EXPORT Job<void> doWhile(const JobContinuation<ControlFlowFlag> &body);
 
 
 
 /**
  * @relates Job
  *
  * Async delay.
  */
 KASYNC_EXPORT Job<void> wait(int delay);
 
 /**
  * @relates Job
  *
  * A null job.
  *
  * An async noop.
  *
  */
 template<typename Out = void>
 Job<Out> null();
 
 /**
  * @relates Job
  *
  * Async value.
  */
 template<typename Out>
 Job<Out> value(Out);
 
 /**
  * @relates Job
  *
  * Async foreach loop.
  *
  * This will execute a job for every value in the list.
  * Errors while not stop processing of other jobs but set an error on the wrapper job.
  */
 template<typename List, typename ValueType = typename List::value_type>
 Job<void, List> forEach(KAsync::Job<void, ValueType> job);
 
 /**
  * @relates Job
  *
  * Async foreach loop.
  *
  * Shorthand that takes a continuation.
  *
  * @see serialForEach
  */
 template<typename List, typename ValueType = typename List::value_type>
  Job<void, List> forEach(JobContinuation<void, ValueType> &&);
 
 
 /**
  * @relates Job
  *
  * Serial Async foreach loop.
  *
  * This will execute a job for every value in the list sequentially.
  * Errors while not stop processing of other jobs but set an error on the wrapper job.
  */
 template<typename List, typename ValueType = typename List::value_type>
 Job<void, List> serialForEach(KAsync::Job<void, ValueType> job);
 
 /**
  * @relates Job
  *
  * Serial Async foreach loop.
  *
  * Shorthand that takes a continuation.
  *
  * @see serialForEach
  */
 template<typename List, typename ValueType = typename List::value_type>
 Job<void, List> serialForEach(JobContinuation<void, ValueType> &&);
 
 /**
  * @brief Wait until all given futures are completed.
  */
 template<template<typename> class Container>
 Job<void> waitForCompletion(Container<KAsync::Future<void>> &futures);
 
 /**
  * @relates Job
  *
  * An error job.
  *
  * An async error.
  *
  */
 template<typename Out = void>
 Job<Out> error(int errorCode = 1, const QString &errorMessage = QString());
 
 /**
  * @relates Job
  *
  * An error job.
  *
  * An async error.
  *
  */
 template<typename Out = void>
 Job<Out> error(const char *);
 
 /**
  * @relates Job
  *
  * An error job.
  *
  * An async error.
  *
  */
 template<typename Out = void>
 Job<Out> error(const Error &);
 
 //@cond PRIVATE
 class KASYNC_EXPORT JobBase
 {
     template<typename Out, typename ... In>
     friend class Job;
 
 public:
     explicit JobBase(const Private::ExecutorBasePtr &executor)
         : mExecutor(executor)
     {}
 
     virtual ~JobBase() = default;
 
 protected:
     Private::ExecutorBasePtr mExecutor;
 };
 //@endcond
 
 /**
  * @brief An Asynchronous job
  *
  * A single instance of Job represents a single method that will be executed
  * asynchronously. The Job is started by exec(), which returns Future
  * immediately. The Future will be set to finished state once the asynchronous
  * task has finished. You can use Future::waitForFinished() to wait for
  * for the Future in blocking manner.
  *
  * It is possible to chain multiple Jobs one after another in different fashion
  * (sequential, parallel, etc.). Calling exec() will then return a pending
  * Future, and will execute the entire chain of jobs.
  *
  * @code
  * auto job = Job::start<QList<int>>(
  *     [](KAsync::Future<QList<int>> &future) {
  *         MyREST::PendingUsers *pu = MyREST::requestListOfUsers();
  *         QObject::connect(pu, &PendingOperation::finished,
  *                          [&](PendingOperation *pu) {
  *                              future->setValue(dynamic_cast<MyREST::PendingUsers*>(pu)->userIds());
  *                              future->setFinished();
  *                          });
  *      })
  * .each<QList<MyREST::User>, int>(
  *      [](const int &userId, KAsync::Future<QList<MyREST::User>> &future) {
  *          MyREST::PendingUser *pu = MyREST::requestUserDetails(userId);
  *          QObject::connect(pu, &PendingOperation::finished,
  *                           [&](PendingOperation *pu) {
  *                              future->setValue(Qlist<MyREST::User>() << dynamic_cast<MyREST::PendingUser*>(pu)->user());
  *                              future->setFinished();
  *                           });
  *      });
  *
  * KAsync::Future<QList<MyREST::User>> usersFuture = job.exec();
  * usersFuture.waitForFinished();
  * QList<MyRest::User> users = usersFuture.value();
  * @endcode
  *
  * In the example above, calling @p job.exec() will first invoke the first job,
  * which will retrieve a list of IDs and then will invoke the second function
  * for each single entry in the list returned by the first function.
  */
 template<typename Out, typename ... In>
 class [[nodiscard]] Job : public JobBase
 {
     //@cond PRIVATE
     template<typename OutOther, typename ... InOther>
     friend class Job;
 
     template<typename OutOther, typename ... InOther>
     friend Job<OutOther, InOther ...> Private::startImpl(Private::ContinuationHolder<OutOther, InOther ...> &&);
 
     template<typename List, typename ValueType>
     friend  Job<void, List> forEach(KAsync::Job<void, ValueType> job);
 
     template<typename List, typename ValueType>
     friend Job<void, List> serialForEach(KAsync::Job<void, ValueType> job);
 
     // Used to disable implicit conversion of Job<void to Job<void> which triggers
     // comiler warning.
     struct IncompleteType;
     //@endcond
 
 public:
     typedef Out OutType;
 
     ///A continuation
     template<typename OutOther, typename ... InOther>
     Job<OutOther, In ...> then(const Job<OutOther, InOther ...> &job) const;
 
     ///Shorthands for a job that returns another job from it's continuation
     //
     //OutOther and InOther are only there fore backwards compatibility, but are otherwise ignored.
     //It should never be necessary to specify any template arguments, as they are automatically deduced from the provided argument.
     //
     //We currently have to write a then overload for:
     //* One argument in the continuation
     //* No argument in the continuation
     //* One argument + error in the continuation
     //* No argument + error in the continuation
     //This is due to how we extract the return type with "decltype(func(std::declval<Out>()))".
     //Ideally we could conflate this into at least fewer overloads, but I didn't manage so far and this at least works as expected.
 
     ///Continuation returning job: [] (Arg) -> KAsync::Job<...> { ... }
     template<typename OutOther = void, typename ... InOther, typename F>
     auto then(F &&func) const -> std::enable_if_t<std::is_base_of<JobBase, decltype(func(std::declval<Out>()))>::value,
                                                   Job<typename decltype(func(std::declval<Out>()))::OutType, In...>>
     {
         using ResultJob = decltype(func(std::declval<Out>())); //Job<QString, int>
         return thenImpl<typename ResultJob::OutType, Out>(
                 {JobContinuation<typename ResultJob::OutType, Out>(std::forward<F>(func))}, Private::ExecutionFlag::GoodCase);
     }
 
     ///Void continuation with job: [] () -> KAsync::Job<...> { ... }
     template<typename OutOther = void, typename ... InOther, typename F>
     auto then(F &&func) const -> std::enable_if_t<std::is_base_of<JobBase, decltype(func())>::value,
                                                   Job<typename decltype(func())::OutType, In...>>
     {
         using ResultJob = decltype(func()); //Job<QString, void>
         return thenImpl<typename ResultJob::OutType>(
                 {JobContinuation<typename ResultJob::OutType>(std::forward<F>(func))}, Private::ExecutionFlag::GoodCase);
     }
 
     ///Error continuation returning job: [] (KAsync::Error, Arg) -> KAsync::Job<...> { ... }
     template<typename OutOther = void, typename ... InOther, typename F>
     auto then(F &&func) const -> std::enable_if_t<std::is_base_of<JobBase, decltype(func(KAsync::Error{}, std::declval<Out>()))>::value,
                                                   Job<typename decltype(func(KAsync::Error{}, std::declval<Out>()))::OutType, In...>>
     {
         using ResultJob = decltype(func(KAsync::Error{}, std::declval<Out>())); //Job<QString, int>
         return thenImpl<typename ResultJob::OutType, Out>(
                 {JobErrorContinuation<typename ResultJob::OutType, Out>(std::forward<F>(func))}, Private::ExecutionFlag::Always);
     }
 
     ///Error void continuation returning job: [] (KAsync::Error) -> KAsync::Job<...> { ... }
     template<typename OutOther = void, typename ... InOther, typename F>
     auto then(F &&func) const -> std::enable_if_t<std::is_base_of<JobBase, decltype(func(KAsync::Error{}))>::value,
                                                   Job<typename decltype(func(KAsync::Error{}))::OutType, In...>>
     {
         using ResultJob = decltype(func(KAsync::Error{}));
         return thenImpl<typename ResultJob::OutType>(
                 {JobErrorContinuation<typename ResultJob::OutType>(std::forward<F>(func))}, Private::ExecutionFlag::Always);
     }
 
     ///Sync continuation: [] (Arg) -> void { ... }
     template<typename OutOther = void, typename ... InOther, typename F>
     auto then(F &&func) const -> std::enable_if_t<!std::is_base_of<JobBase, decltype(func(std::declval<Out>()))>::value,
                                                   Job<decltype(func(std::declval<Out>())), In...>>
     {
         using ResultType = decltype(func(std::declval<Out>())); //QString
         return thenImpl<ResultType, Out>(
                 {SyncContinuation<ResultType, Out>(std::forward<F>(func))}, Private::ExecutionFlag::GoodCase);
     }
 
     ///Sync void continuation: [] () -> void { ... }
     template<typename OutOther = void, typename ... InOther, typename F>
     auto then(F &&func) const -> std::enable_if_t<!std::is_base_of<JobBase, decltype(func())>::value,
                                                   Job<decltype(func()), In...>>
     {
         using ResultType = decltype(func()); //QString
         return thenImpl<ResultType>(
                 {SyncContinuation<ResultType>(std::forward<F>(func))}, Private::ExecutionFlag::GoodCase);
     }
 
     ///Sync error continuation: [] (KAsync::Error, Arg) -> void { ... }
     template<typename OutOther = void, typename ... InOther, typename F>
     auto then(F &&func) const -> std::enable_if_t<!std::is_base_of<JobBase, decltype(func(KAsync::Error{}, std::declval<Out>()))>::value,
                                                   Job<decltype(func(KAsync::Error{}, std::declval<Out>())),In...>>
     {
         using ResultType = decltype(func(KAsync::Error{}, std::declval<Out>())); //QString
         return thenImpl<ResultType, Out>(
                 {SyncErrorContinuation<ResultType, Out>(std::forward<F>(func))}, Private::ExecutionFlag::Always);
     }
 
     ///Sync void error continuation: [] (KAsync::Error) -> void { ... }
     template<typename OutOther = void, typename ... InOther, typename F>
     auto then(F &&func) const -> std::enable_if_t<!std::is_base_of<JobBase, decltype(func(KAsync::Error{}))>::value,
                                                   Job<decltype(func(KAsync::Error{})), In...>>
     {
         using ResultType = decltype(func(KAsync::Error{}));
         return thenImpl<ResultType>(
                 {SyncErrorContinuation<ResultType>(std::forward<F>(func))}, Private::ExecutionFlag::Always);
     }
 
     ///Shorthand for a job that receives the error and a handle
     template<typename OutOther, typename ... InOther>
     Job<OutOther, In ...> then(AsyncContinuation<OutOther, InOther ...> &&func) const
     {
         return thenImpl<OutOther, InOther ...>({std::forward<AsyncContinuation<OutOther, InOther ...>>(func)},
                                                Private::ExecutionFlag::GoodCase);
     }
 
     ///Shorthand for a job that receives the error and a handle
     template<typename OutOther, typename ... InOther>
     Job<OutOther, In ...> then(AsyncErrorContinuation<OutOther, InOther ...> &&func) const
     {
         return thenImpl<OutOther, InOther ...>({std::forward<AsyncErrorContinuation<OutOther, InOther ...>>(func)}, Private::ExecutionFlag::Always);
     }
 
     ///Shorthand for a job that receives the error only
     Job<Out, In ...> onError(SyncErrorContinuation<void> &&errorFunc) const;
 
     /**
      * Shorthand for a forEach loop that automatically uses the return type of
      * this job to deduce the type expected.
      */
     template<typename OutOther = void, typename ListType = Out, typename ValueType = typename ListType::value_type, std::enable_if_t<!std::is_void<ListType>::value, int> = 0>
     Job<void, In ...> each(JobContinuation<void, ValueType> &&func) const
     {
         eachInvariants<OutOther>();
         return then<void, In ...>(forEach<Out, ValueType>(std::forward<JobContinuation<void, ValueType>>(func)));
     }
 
     /**
      * Shorthand for a serialForEach loop that automatically uses the return type
      * of this job to deduce the type expected.
      */
     template<typename OutOther = void, typename ListType = Out, typename ValueType = typename ListType::value_type, std::enable_if_t<!std::is_void<ListType>::value, int> = 0>
     Job<void, In ...> serialEach(JobContinuation<void, ValueType> &&func) const
     {
         eachInvariants<OutOther>();
         return then<void, In ...>(serialForEach<Out, ValueType>(std::forward<JobContinuation<void, ValueType>>(func)));
     }
 
     /**
      * Enable implicit conversion to Job<void>.
      *
      * This is necessary in assignments that only use the return value (which is the normal case).
      * This avoids constructs like:
      * auto job = KAsync::start<int>( ... )
      *  .then<void, int>( ... )
      *  .then<void>([](){}); //Necessary for the assignment without the implicit conversion
      */
     template<typename ... InOther>
     operator std::conditional_t<std::is_void<OutType>::value, IncompleteType, Job<void>>();
 
     /**
      * Adds an unnamed value to the context.
      * The context is guaranteed to persist until the jobs execution has finished.
      *
      * Useful for setting smart pointer to manage lifetime of objects required
      * during the execution of the job.
      */
     template<typename T>
     Job<Out, In ...> &addToContext(const T &value)
     {
         assert(mExecutor);
         mExecutor->addToContext(QVariant::fromValue<T>(value));
         return *this;
     }
 
     /**
      * Adds a guard.
      * It is guaranteed that no callback is executed after the guard vanishes.
      *
      * Use this i.e. ensure you don't call-back into an already destroyed object.
      */
     Job<Out, In ...> &guard(const QObject *o)
     {
         assert(mExecutor);
         mExecutor->guard(o);
         return *this;
     }
 
     /**
      * @brief Starts execution of the job chain.
      *
      * This will start the execution of the task chain, starting from the
      * first one. It is possible to call this function multiple times, each
      * invocation will start a new processing and provide a new Future to
      * watch its status.
      *
      * @param in Argument to be passed to the very first task
      * @return Future&lt;Out&gt; object which will contain result of the last
      * task once if finishes executing. See Future documentation for more details.
      *
      * @see exec(), Future
      */
     template<typename FirstIn>
     KAsync::Future<Out> exec(FirstIn in);
 
     /**
      * @brief Starts execution of the job chain.
      *
      * This will start the execution of the task chain, starting from the
      * first one. It is possible to call this function multiple times, each
      * invocation will start a new processing and provide a new Future to
      * watch its status.
      *
      * @return Future&lt;Out&gt; object which will contain result of the last
      * task once if finishes executing. See Future documentation for more details.
      *
      * @see exec(FirstIn in), Future
      */
     KAsync::Future<Out> exec();
 
     explicit Job(JobContinuation<Out, In ...> &&func);
     explicit Job(AsyncContinuation<Out, In ...> &&func);
 
 private:
     //@cond PRIVATE
     explicit Job(Private::ExecutorBasePtr executor);
 
     template<typename OutOther, typename ... InOther>
     Job<OutOther, In ...> thenImpl(Private::ContinuationHolder<OutOther, InOther ...> helper,
                                    Private::ExecutionFlag execFlag = Private::ExecutionFlag::GoodCase) const;
 
     template<typename InOther, typename ... InOtherTail>
     void thenInvariants() const;
 
     //Base case for an empty parameter pack
     template<typename ... InOther>
     auto thenInvariants() const -> std::enable_if_t<(sizeof...(InOther) == 0)>;
 
     template<typename OutOther>
     void eachInvariants() const;
     //@endcond
 };
 
 } // namespace KAsync
 
 
 // out-of-line definitions of Job methods
 #include "job_impl.h"
 
 #endif // KASYNC_H