recursivelock.inl

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//==================================================================================================
/// \file
/// This header-file is part of module \alib_threads of the \aliblong.
///
/// \emoji :copyright: 2013-2025 A-Worx GmbH, Germany.
/// Published under \ref mainpage_license "Boost Software License".
//==================================================================================================
#if !ALIB_SINGLE_THREADED
ALIB_EXPORT namespace alib {  namespace threads {
 
//==================================================================================================
/// This class is a simple wrapper around C++ standard library type \c std::recursive_mutex.
/// Thus, it is used to implement <em>mutual exclusive access</em> to resources by protecting
/// critical code sections from being executed in parallel in concurrent threads.
///
/// When a pair of #AcquireRecursive and #ReleaseRecursive invocations is performed within the same
/// code block, then it is recommended to use a stack instantiation of class
/// \alib{lang;OwnerRecursive} to acquire and release objects of this class.
/// Such a use is highly simplified with macros \ref ALIB_LOCK_RECURSIVE and
/// \ref ALIB_LOCK_RECURSIVE_WITH.
///
/// Nested acquisitions are supported with this type.
/// An instance of this class is released when an equal number of invocations to #AcquireRecursive
/// and #ReleaseRecursive have been performed.<br>
/// This class has slightly reduced performance in comparison to non-recursive type
/// \alib{threads;Lock}. Not only for this reason, non-nested locking is the preferred technique.
/// But there are situations where nested locks are just unavoidable.
///
/// \par Debug-Features
/// Public member #Dbg is available with debug-compilations. It offers the following features:
/// - The object stores the actual owning thread and the source code position of the last
///   acquirement.
/// - Releasing non-acquired instances, as well as destructing acquired one, raise an assertion.
/// - A warning threshold for the number of nested acquisitions can be defined with public member
///   \alib{threads;DbgLockAsserter::RecursionLimit}.
/// - Field \alib{threads;DbgLockAsserter;WaitTimeLimit} enables the raise of \alib warnings in case a
///   certain wait time is exceeded.
///   Note that instead of wrapping \c std::recursive_mutex, with debug-compilations class
///   \c std::recursive_timed_mutex is wrapped.
///
/// \par Availability
/// This type is not available if the compiler-symbol \ref ALIB_SINGLE_THREADED is set.
///
/// @see
///   - Chapter \ref alib_threads_locks of the Programmer's Manual of the module \alib_threads_nl.
///   - Chapter \ref alib_manual_appendix_callerinfo of the General Programmer's Manual.
//==================================================================================================
class RecursiveLock
#if ALIB_DEBUG_CRITICAL_SECTIONS
: public lang::DbgCriticalSections::AssociatedLock
#endif
{
  protected:
  #if !ALIB_DEBUG && !DOXYGEN
    std::recursive_mutex            mutex; // the only member in release compilations
 
  #else
    #if DOXYGEN
        /// The internal object to lock on.
        /// \note With debug-compilations, this is of type <c>std::recursive_timed_mutex</c>.
        std::recursive_mutex        mutex;
    #else
    std::recursive_timed_mutex  mutex;
    #endif
 
  public:
    /// The debug tool instance.
    DbgLockAsserter                  Dbg;
  #endif
 
 
    #if ALIB_DEBUG_CRITICAL_SECTIONS
    /// @return \c true if the lock is acquired (in non-shared mode), \c false otherwise.
    ALIB_DLL virtual bool DCSIsAcquired()                                            const override;
 
    /// @return \c true if the lock is shared-acquired (by at least any thread).
    ///            Otherwise, returns \c false.
    ALIB_DLL virtual bool DCSIsSharedAcquired()                                      const override;
    #endif
 
  //################################################################################################
  // Interface
  //################################################################################################
  public:
 
  #if ALIB_DEBUG || DOXYGEN
    /// Thread which invokes this method gets registered as the current owner of this object,
    /// until the same thread releases the ownership invoking #ReleaseRecursive.
    /// In the case that this object is already owned by another thread, the invoking thread is
    /// suspended until ownership can be gained.
    /// Multiple (nested) calls to this method are counted and the object is only released when
    /// the same number of Release() calls have been made.
    ///
    /// \par Debug Parameter:
    ///   Pass macro \ref ALIB_CALLER_PRUNED with invocations.
    ALIB_DLL
    void        AcquireRecursive( ALIB_DBG_TAKE_CI );
 
    /// Tries to acquire this lock.
    /// Successful calls to this method are counted, as if #AcquireRecursive was called and an
    /// according invocation of #ReleaseRecursive has to be performed.
    ///
    /// \par Debug Parameter:
    ///   Pass macro \ref ALIB_CALLER_PRUNED with invocations.
    ///
    /// @return \c true if the lock was not acquired by a different thread and thus, this
    ///         call was successful. \c false otherwise.
    ALIB_DLL
    [[nodiscard]]
    bool TryAcquire( ALIB_DBG_TAKE_CI );
  #else
                   void  AcquireRecursive()                                        { mutex.lock(); }
    [[nodiscard]]  bool  TryAcquire()                                   { return mutex.try_lock(); }
  #endif
 
  #if ALIB_DEBUG || DOXYGEN
    /// Releases ownership of this object. If #AcquireRecursive was called multiple times before,
    /// the same number of calls to this method has to be performed to release ownership.
    /// \par Debug Parameter:
    ///   Pass macro \ref ALIB_CALLER_PRUNED with invocations.
    ALIB_DLL
    void        ReleaseRecursive( ALIB_DBG_TAKE_CI );
  #else
    void       ReleaseRecursive()                                                { mutex.unlock(); }
  #endif
};
 
 
} // namespace alib[threads]
 
/// Type alias in namespace \b alib.
using     RecursiveLock=   threads::RecursiveLock;
 
} // namespace [alib]
#endif // !ALIB_SINGLE_THREADED