WaitableEvent.h

/*
 * Copyright(c) Sophist Solutions, Inc. 1990-2026.  All rights reserved
 */
#ifndef _Stroika_Foundation_Execution_WaitableEvent_h_
#define _Stroika_Foundation_Execution_WaitableEvent_h_ 1
 
#include "Stroika/Foundation/StroikaPreComp.h"
 
#include <forward_list>
#include <set>
 
#include "Stroika/Foundation/Common/Common.h"
#include "Stroika/Foundation/Execution/ConditionVariable.h"
#include "Stroika/Foundation/Execution/SpinLock.h"
 
/**
 *  \note Code-Status:  <a href="Code-Status.md#Beta">Beta</a>
 */
 
namespace Stroika::Foundation::Execution {
 
    /*
     *  UNSURE IF/HOW LONG WE WANT TO SUPPORT THIS API. EXPERIMENTAL!
     *  (introduced in Stroika 2.0a20 - 2014-02-08)
     * 
     *      This appears to be an issue with strong arguments on both sides. I'm very uncertain.
     *
     *      I've used the Windows WaitForMutlipleObjects API for years, and feel pretty comfortable with it.
     *      I find it handy.
     *
     *      However, there are compelling arguments (for example):
     *          https://groups.google.com/forum/#!msg/comp.unix.programmer/q2x0yQR5txk/34v1qQZN_u0J
     *          https://groups.google.com/forum/#!msg/comp.unix.programmer/WsgZZmu4ESA/Rv1MCun1CmUJ
     *
     *      which argue that its a bad idea, and that it leads to bad programming (bugs).
     *
     *      To some extent I we may have addressed the reported concerns by having WaitForAny/WaitForAnyUntil
     *      return the full set of events that were signaled (and the issue about races I don't think applies
     *      to WaitForAll).
     *
     *      Note also that some recommend using the BlockingQueue<> pattern to avoid WaitForMultipleObjects (WaitForAny)
     *      such as:
     *              http://stackoverflow.com/questions/788835/waitformultipleobjects-in-java
     *      Stroika supports this sort of BlockingQueue<>
     *
     *      Note - WaitForAny() takes a templated SET because I don't want to create interdependency
     *      with Containers and something this low level, and yet we want to make it easy for users of this
     *      to use Stroika Set<> objects.
     *
     *      References:
     *          o   Notes on implementing Windows WaitForMultipleEvents API using POSIX (which are similar to stdc++) APIs:
     *              https://www.hackerzvoice.net/madchat/windoz/coding/winapi/waitfor_api.pdf
     *
     *          o   Interesting notes on how to implement WaitForMultipleEvents
     *              http://lists.boost.org/Archives/boost/2004/12/77175.php
     *
     *  I THINK condition-variable API is better, so disabling this by default.. and maybe lose it altogether soon.
     *  -- LGP 2023-10-17
     */
#ifndef qStroika_Foundation_Execution_WaitableEvent_SupportWaitForMultipleObjects
#if defined(qExecution_WaitableEvent_SupportWaitForMultipleObjects)
#define qStroika_Foundation_Execution_WaitableEvent_SupportWaitForMultipleObjects qExecution_WaitableEvent_SupportWaitForMultipleObjects
#else
#define qStroika_Foundation_Execution_WaitableEvent_SupportWaitForMultipleObjects 0
#endif
#endif
// DEPRECATED NAME - since 3.0d25 (to be removed in v3.0a1)
#ifndef qExecution_WaitableEvent_SupportWaitForMultipleObjects
#define qExecution_WaitableEvent_SupportWaitForMultipleObjects qStroika_Foundation_Execution_WaitableEvent_SupportWaitForMultipleObjects
#endif
 
    /**
     *  AutoReset Waitable Event (like Windows' CreateEvent (resetType==eManualReset, false)).
     *
     *  \note   \em Thread-Safety   <a href="Thread-Safety.md#Internally-Synchronized-Thread-Safety">Internally-Synchronized-Thread-Safety</a>
     *
     *  \note   \em async-signal-safety - this is NOT safe to use from signals (from http://pubs.opengroup.org/onlinepubs/009695399/functions/pthread_cond_broadcast.html - It is not safe to use the pthread_cond_signal() function in a signal handler that is invoked asynchronously
     *          Use POSIX sem_init/sem_post () 
     *
     *  \note   \em Design Note     Considered making this copyable, or at least movable, but mutex and
     *              other similar classes are not.
     *              and you can easily use shared_ptr<> on an WaitableEvent to make it copyable.
     *
     *  \note   \em Design Note     WaitForAny/WaitForAnyUntil and WaitForMultipleEvents
     *
     *  @see    qStroika_Foundation_Execution_WaitableEvent_SupportWaitForMultipleObjects
     */
    class WaitableEvent {
    public:
        /**
         */
        WaitableEvent ();
        WaitableEvent (WaitableEvent&&)      = delete;
        WaitableEvent (const WaitableEvent&) = delete;
 
    public:
        /**
         *  \note the user of this class must assure all waiters have completed their wait before destroying the event (checked with assertions).
         */
#if qStroika_Foundation_Debug_AssertionsChecked
        ~WaitableEvent ();
#else
        ~WaitableEvent () = default;
#endif
 
    public:
        nonvirtual WaitableEvent& operator= (const WaitableEvent&&) = delete;
        nonvirtual WaitableEvent& operator= (const WaitableEvent&)  = delete;
 
    public:
        /**
         *  Set the event to the non-signaled state
         *
         *  \note   This COULD have been called 'UnSet'.
         *
         *  \note   ***Not Cancelation Point***
         */
        nonvirtual void Reset ();
 
    public:
        /**
         *  This checks if the event is currently in a triggered state. Regardless of the type of event
         *  (auto-reset or not) - this does not change the trigger state.
         *
         *  \note   ***Not Cancelation Point***
         */
        nonvirtual bool GetIsSet () const noexcept;
 
    public:
        /**
         *  This checks if the event is currently in a triggered state. Regardless of the type of event
         *  (auto-reset or not) - this does not change the trigger state.
         * 
         *  \note   ***NOT THREADSAFE*** - same as GetIsSet() except avoids the lock, so will be reported by TSAN (for example)
         *          as a race (cuz it is). JUST INTENDED for debug trace messages (so used in ToString).
         * 
         *          Because of this - if testing with TSAN (thread sanitizer) - probably best to prefix functions calling this with
         *          Stroika_Foundation_Debug_ATTRIBUTE_NO_SANITIZE_THREAD
         *
         *  \note   ***Not Cancelation Point***
         */
        nonvirtual bool PeekIsSet () const noexcept;
 
    public:
        /**
         *  Set the event to the signaled state.
         *
         *  \note   This COULD have been called 'Signal', or 'SetSignaled'.
         *
         *  \note   ***Not Cancelation Point***, but can throw (cuz uses mutex lock which can throw)
         */
        nonvirtual void Set ();
 
    public:
        /**
         *  Simple wait. Can use operator HANDLE() to do fancier waits.
         *  timeout can be negative (which triggers an immediate exception).
         *
         *  Throws a timeout (@see Execution::ThrowError (errc::timed_out)) if the timeout is exceeded.
         *
         *  \note Wait (0) will always throw a timeout regardless of the state of the event/trigger
         *
         *  @see WaitQuietly ()
         *  @see PeekIsSet ()
         *
         *  \note   ***Cancelation Point***
         */
        nonvirtual void Wait (Time::DurationSeconds timeout = Time::kInfinity);
 
    public:
        /**
         *  Intentionally omit case of spurious wakeup we get from condition variables.
         */
        enum class WaitStatus {
            eTimeout,
            eTriggered,
 
            Stroika_Define_Enum_Bounds (eTimeout, eTriggered)
        };
 
    public:
        /**
         *  Wait the given period of time, and return true if event occurred (Set called), and false on timeout.
         *  This is mostly useful if we want a wait, for advisory purposes (say to avoid races), but don't
         *  want an exception as its not an issue to handle specially.
         *
         *  Returns:    true (kWaitQuietlySetResult) if event signaled/occurred, and false (kWaitQuietlyTimeoutResult) if timeout
         *
         *  \note   WaitQuietly (0) will always return false regardless of the state of the event/trigger
         *
         *  \note   WaitQuietly() can raise exceptions, but only Thread::AborttException
         *
         *  @see Wait ()
         *  @see WaitUntil ()
         *  @see WaitUntilQuietly ()
         *  @see WaitQuietlyAndReset ()
         *  @see PeekIsSet ()
         *
         *  \note   ***Cancelation Point***
         */
        nonvirtual WaitStatus WaitQuietly (Time::DurationSeconds timeout = Time::kInfinity);
 
    public:
        /**
         *  Throws a timeout (@see Execution::ThrowError (errc::timed_out)) if the event is not signaled before timeoutAt is
         *  exceeded (includes when reached).
         *
         *  @see Wait ()
         *  @see WaitQuietly ()
         *  @see WaitUntilQuietly ()
         *  @see WaitUntilAndReset ()
         *
         *  \note   ***Cancelation Point***
         */
        nonvirtual void WaitUntil (Time::TimePointSeconds timeoutAt);
 
    public:
        /**
         *
         *  \note   WaitUntilQuietly() can raise exceptions, but only Thread::AbortException
         *
         *  Returns:    true (kWaitQuietlySetResult) if event signaled/occurred, and false (kWaitQuietlyTimeoutResult) if timeout
         * 
         *  Note - unlike condition variable - will not return with spurious wakeup.
         *  So a return of triggered means it definitely was triggered!
         *
         *  @see Wait ()
         *  @see WaitQuietly ()
         *  @see WaitUntil ()
         *  @see WaitUntilQuietlyAndReset ()
         *
         *  \note   ***Cancelation Point***
         */
        nonvirtual WaitStatus WaitUntilQuietly (Time::TimePointSeconds timeoutAt);
 
    public:
        /**
         *  @see Wait ()
         *  @see WaitUntil ()
         *  @see WaitQuietly ()
         *  @see WaitUntilQuietly ()
         *  @see Reset ()
         *
         *  \note   ***Cancelation Point***
         * 
         *  Unclear if this is a good idea. Its a preplacement for 'auto-reset' events in Stroika v2.1.
         */
        nonvirtual void       WaitAndReset (Time::Duration timeout = Time::kInfinity);
        nonvirtual void       WaitUntilAndReset (Time::TimePointSeconds timeoutAt);
        nonvirtual WaitStatus WaitQuietlyAndReset (const Time::Duration& timeout);
        nonvirtual WaitStatus WaitUntilQuietlyAndReset (Time::TimePointSeconds timeoutAt);
 
    public:
#if qStroika_Foundation_Execution_WaitableEvent_SupportWaitForMultipleObjects
    public:
        /**
         *  Note - CONTAINER_OF_WAITABLE_EVENTS - must iterate over WaitableEvent*!
         *
         *  \note   WaitForAny IS EXPERIMENTAL
         *
         *  \note   ***Cancelation Point***
         */
        template <typename CONTAINER_OF_WAITABLE_EVENTS, typename SET_OF_WAITABLE_EVENTS_RESULT = set<WaitableEvent*>>
        static SET_OF_WAITABLE_EVENTS_RESULT WaitForAny (CONTAINER_OF_WAITABLE_EVENTS waitableEvents, Time::DurationSeconds timeout = Time::kInfinity);
        template <typename ITERATOR_OF_WAITABLE_EVENTS, typename SET_OF_WAITABLE_EVENTS_RESULT = set<WaitableEvent*>>
        static SET_OF_WAITABLE_EVENTS_RESULT WaitForAny (ITERATOR_OF_WAITABLE_EVENTS waitableEventsStart, ITERATOR_OF_WAITABLE_EVENTS waitableEventsEnd,
                                                         Time::DurationSeconds timeout = Time::kInfinity);
 
    public:
        /**
         *  Note - CONTAINER_OF_WAITABLE_EVENTS - must iterate over WaitableEvent*!
         *
         *  \note   WaitForAny IS EXPERIMENTAL
         *
         *  \note   ***Cancelation Point***
         */
        template <typename CONTAINER_OF_WAITABLE_EVENTS, typename SET_OF_WAITABLE_EVENTS_RESULT = set<WaitableEvent*>>
        static SET_OF_WAITABLE_EVENTS_RESULT WaitForAnyUntil (CONTAINER_OF_WAITABLE_EVENTS waitableEvents, Time::TimePointSeconds timeoutAt);
        template <typename ITERATOR_OF_WAITABLE_EVENTS, typename SET_OF_WAITABLE_EVENTS_RESULT = set<WaitableEvent*>>
        static SET_OF_WAITABLE_EVENTS_RESULT WaitForAnyUntil (ITERATOR_OF_WAITABLE_EVENTS waitableEventsStart,
                                                              ITERATOR_OF_WAITABLE_EVENTS waitableEventsEnd, Time::TimePointSeconds timeoutAt);
 
    public:
        /**
         *  Note - CONTAINER_OF_WAITABLE_EVENTS - must iterate over WaitableEvent*!
         *
         *  \note   WaitForAll IS EXPERIMENTAL
         *
         *  \note   ***Cancelation Point***
         */
        template <typename CONTAINER_OF_WAITABLE_EVENTS>
        static void WaitForAll (CONTAINER_OF_WAITABLE_EVENTS waitableEvents, Time::DurationSeconds timeout = Time::kInfinity);
        template <typename ITERATOR_OF_WAITABLE_EVENTS>
        static void WaitForAll (ITERATOR_OF_WAITABLE_EVENTS waitableEventsStart, ITERATOR_OF_WAITABLE_EVENTS waitableEventsEnd,
                                Time::DurationSeconds timeout = Time::kInfinity);
 
    public:
        /**
         *  Note - CONTAINER_OF_WAITABLE_EVENTS - must iterate over WaitableEvent*!
         *
         *  \note   WaitForAllUntil IS EXPERIMENTAL
         *
         *  \note   ***Cancelation Point***
         */
        template <typename CONTAINER_OF_WAITABLE_EVENTS>
        static void WaitForAllUntil (CONTAINER_OF_WAITABLE_EVENTS waitableEvents, Time::TimePointSeconds timeoutAt);
        template <typename ITERATOR_OF_WAITABLE_EVENTS>
        static void WaitForAllUntil (ITERATOR_OF_WAITABLE_EVENTS waitableEventsStart, ITERATOR_OF_WAITABLE_EVENTS waitableEventsEnd,
                                     Time::TimePointSeconds timeoutAt);
 
    private:
        static inline SpinLock sExtraWaitableEventsMutex_;
#endif
 
    public:
        DISABLE_COMPILER_MSC_WARNING_START (4996);
        DISABLE_COMPILER_GCC_WARNING_START ("GCC diagnostic ignored \"-Wdeprecated-declarations\"");
        DISABLE_COMPILER_CLANG_WARNING_START ("clang diagnostic ignored \"-Wdeprecated-declarations\"");
        enum class [[deprecated ("Since Stroika v3.0d4 - use WaitAndReset")]] ResetType {
            eAutoReset,
            eManualReset,
            Stroika_Define_Enum_Bounds (eAutoReset, eManualReset)
        };
        [[deprecated ("Since Stroika v3.0d4 - use WaitAndReset")]] static constexpr ResetType eAutoReset   = ResetType::eAutoReset;
        [[deprecated ("Since Stroika v3.0d4 - use WaitAndReset")]] static constexpr ResetType eManualReset = ResetType::eManualReset;
        [[deprecated ("since v3.0d4 - use WaitStatus::eTimeout")]] static constexpr WaitStatus kWaitQuietlyTimeoutResult{WaitStatus::eTimeout};
        [[deprecated ("since v3.0d4 - use WaitStatus::eTriggered")]] static constexpr WaitStatus kWaitQuietlySetResult{WaitStatus::eTriggered};
        DISABLE_COMPILER_MSC_WARNING_END (4996);
        DISABLE_COMPILER_GCC_WARNING_END ("GCC diagnostic ignored \"-Wdeprecated-declarations\"");
        DISABLE_COMPILER_CLANG_WARNING_END ("clang diagnostic ignored \"-Wdeprecated-declarations\"");
 
    private:
        struct WE_ {
            mutable ConditionVariable<> fConditionVariable{};
            bool                        fTriggered{false}; // not atomic cuz always examined under a lock (except PeekIsSet for debugging)
 
            nonvirtual void       Reset ();
            nonvirtual bool       GetIsSet () const noexcept;
            nonvirtual bool       PeekIsSet () const noexcept; // just for debugging
            nonvirtual void       Set ();
            nonvirtual void       WaitUntil (Time::TimePointSeconds timeoutAt);
            nonvirtual WaitStatus WaitUntilQuietly (Time::TimePointSeconds timeoutAt);
        };
        WE_ fWE_;
#if qStroika_Foundation_Execution_WaitableEvent_SupportWaitForMultipleObjects
        forward_list<shared_ptr<WE_>> fExtraWaitableEvents_;
#endif
    };
 
}
 
/*
 ********************************************************************************
 ***************************** Implementation Details ***************************
 ********************************************************************************
 */
#include "WaitableEvent.inl"
 
#endif /*_Stroika_Foundation_Execution_WaitableEvent_h_*/