JUCE/modules/juce_core/threads/juce_InterProcessLock.h

/*
  ==============================================================================

   This file is part of the JUCE library.
   Copyright (c) 2017 - ROLI Ltd.

   JUCE is an open source library subject to commercial or open-source
   licensing.

   The code included in this file is provided under the terms of the ISC license
   http://www.isc.org/downloads/software-support-policy/isc-license. Permission
   To use, copy, modify, and/or distribute this software for any purpose with or
   without fee is hereby granted provided that the above copyright notice and
   this permission notice appear in all copies.

   JUCE IS PROVIDED "AS IS" WITHOUT ANY WARRANTY, AND ALL WARRANTIES, WHETHER
   EXPRESSED OR IMPLIED, INCLUDING MERCHANTABILITY AND FITNESS FOR PURPOSE, ARE
   DISCLAIMED.

  ==============================================================================
*/

namespace juce
{

//==============================================================================
/**
    Acts as a critical section which processes can use to block each other.

    @see CriticalSection
*/
class JUCE_API  InterProcessLock
{
public:
    //==============================================================================
    /** Creates a lock object.
        @param name   a name that processes will use to identify this lock object
    */
    explicit InterProcessLock (const String& name);

    /** Destructor.
        This will also release the lock if it's currently held by this process.
    */
    ~InterProcessLock();

    //==============================================================================
    /** Attempts to lock the critical section.

        @param timeOutMillisecs  how many milliseconds to wait if the lock is already
                                 held by another process - a value of 0 will return
                                 immediately, negative values will wait forever
        @returns    true if the lock could be gained within the timeout period, or
                    false if the timeout expired.
    */
    bool enter (int timeOutMillisecs = -1);

    /** Releases the lock if it's currently held by this process. */
    void exit();

    //==============================================================================
    /**
        Automatically locks and unlocks an InterProcessLock object.

        This works like a ScopedLock, but using an InterprocessLock rather than
        a CriticalSection.

        @see ScopedLock
    */
    class ScopedLockType
    {
    public:
        //==============================================================================
        /** Creates a scoped lock.

            As soon as it is created, this will lock the InterProcessLock, and
            when the ScopedLockType object is deleted, the InterProcessLock will
            be unlocked.

            Note that since an InterprocessLock can fail due to errors, you should check
            isLocked() to make sure that the lock was successful before using it.

            Make sure this object is created and deleted by the same thread,
            otherwise there are no guarantees what will happen! Best just to use it
            as a local stack object, rather than creating one with the new() operator.
        */
        explicit ScopedLockType (InterProcessLock& l)        : ipLock (l) { lockWasSuccessful = l.enter(); }

        /** Destructor.

            The InterProcessLock will be unlocked when the destructor is called.

            Make sure this object is created and deleted by the same thread,
            otherwise there are no guarantees what will happen!
        */
        inline ~ScopedLockType()                             { ipLock.exit(); }

        /** Returns true if the InterProcessLock was successfully locked. */
        bool isLocked() const noexcept                       { return lockWasSuccessful; }

    private:
        //==============================================================================
        InterProcessLock& ipLock;
        bool lockWasSuccessful;

        JUCE_DECLARE_NON_COPYABLE (ScopedLockType)
    };

private:
    //==============================================================================
    class Pimpl;
    friend struct ContainerDeletePolicy<Pimpl>;
    ScopedPointer<Pimpl> pimpl;

    CriticalSection lock;
    String name;

    JUCE_DECLARE_NON_COPYABLE (InterProcessLock)
};

} // namespace juce