_ak_fifo_queue_8h

Other Documentation

Wwise SDK 2022.1.4

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 #ifndef _AKFIFOQUEUE_H

 #define _AKFIFOQUEUE_H

 #include <AK/SoundEngine/Common/AkTypes.h>

 #include <AK/SoundEngine/Common/AkAtomic.h>

 #include <AK/Tools/Common/AkArray.h>

 /// AkFifoQueue is a lock-less, thread-safe, multi-producer-multi-consumer queue data structure.

 /// It is designed to hold copyable values.

 template<typename T, T TDEFAULT, class TAlloc = ArrayPoolDefault>

 struct AkFifoQueue : public TAlloc

 {

 public:

     AkFifoQueue()

         : m_buffer(nullptr)

         , m_uQueueIndexMask(0)

         , m_readPos(0)

         , m_writePos(0)

     {

     }

     ~AkFifoQueue()

     {

         Term();

     }

     /// Initializes the FifoQueue and allocates memory for the specified number of entries.

     /// The number of entries is not growable after initialization.

     AKRESULT Init(

         AkUInt32 in_uMaxEntries      ///< The number of entries. Must be a power of two.

         )

     {

         // check that maxentries is a power of 2

         AKASSERT((in_uMaxEntries & (in_uMaxEntries - 1)) == 0);

         m_uQueueIndexMask = in_uMaxEntries - 1;

         m_writePos = 0;

         m_readPos = 0;

         m_buffer = (FifoQueueEntry*)TAlloc::Alloc(sizeof(FifoQueueEntry) * in_uMaxEntries);

         if (m_buffer == nullptr)

         {

             return AK_InsufficientMemory;

         }

         AkZeroMemLarge(m_buffer, sizeof(FifoQueueEntry) * in_uMaxEntries);

         for (AkUInt32 i = 0; i < in_uMaxEntries; ++i)

         {

             m_buffer[i].value = TDEFAULT;

             AkAtomicStore64(&m_buffer[i].uSequence, i);

         }

         return AK_Success;

     }

     /// Free memory reserved for the queue and reset internal state

     /// The queue MUST be empty when this is called!

     void Term()

     {

         if (m_buffer)

         {

             AKASSERT(m_readPos == m_writePos);

             TAlloc::Free(m_buffer);

             m_buffer = nullptr;

         }

         m_readPos = 0;

         m_writePos = 0;

     }

     /// Enqueues the provided value. The value will be copied to the queue's internal buffer.

     /// Returns true if the enqueue was performed successfully.

     /// Returns false if the enqueue could not be performed. This can happen if the queue is "full", and some dequeue operations have to occur.

     AK_NODISCARD bool Enqueue(T in_value)

     {

         const AkUInt64 uQueueIndexMask = m_uQueueIndexMask;

         FifoQueueEntry* pBuffer = m_buffer;

         AkInt64 writePos = AkAtomicLoad64(&m_writePos);

         do {

             // see where we are in the sequence, relative to where we can write data

             AkInt64 sequenceDelta = AkAtomicLoad64(&pBuffer[writePos & uQueueIndexMask].uSequence) - writePos;

             // if we're in the right spot, and we can successfully write an updated write position, break out and write the handle into the queue

             if (sequenceDelta == 0)

             {

                 if (AkAtomicCas64(&m_writePos, writePos + 1, writePos))

                 {

                     break;

                 }

             }

             else if (sequenceDelta < 0)

             {

                 // we would have over-enqueued if we tried to write the position in. Return false; the user needs to decide how to handle things

                 return false;

             }

             else

             {

                 // if it didn't work, reload writePos: someone else must have written to the sequence and we need to get caught up

                 writePos = AkAtomicLoad64(&m_writePos);

             }

         } while (true);

         // advance the sequence by one so that it can be dequeued

         pBuffer[writePos & uQueueIndexMask].value = in_value;

         AkAtomicStore64(&pBuffer[writePos & uQueueIndexMask].uSequence, writePos + 1);

         return true;

     }

     /// Dequeues a value from the specified queue, copying it to io_value

     /// \return true if a value was successfully dequeued, false otherwise (if false, io_value will not be written to)

     bool Dequeue(T& io_value)

     {

         const AkInt64 uQueueIndexMask = m_uQueueIndexMask;

         FifoQueueEntry* pBuffer = m_buffer;

         AkInt64 readPos = AkAtomicLoad64(&m_readPos);

         do {

             // see where we are in the sequence relative to where we can write data

             AkInt64 sequenceDelta = AkAtomicLoad64(&pBuffer[readPos & uQueueIndexMask].uSequence) - (readPos + 1);

             // if we're in the right spot, and we can successfully write an updated read position, break out and read the entry

             if (sequenceDelta == 0)

             {

                 if (AkAtomicCas64(&m_readPos, readPos + 1, readPos))

                 {

                     break;

                 }

             }

             // if an entry has yet to be written, bail out

             else if (sequenceDelta < 0)

             {

                 return false;

             }

             else

             {

                 // if it didn't work, reload readPos

                 readPos = AkAtomicLoad64(&m_readPos);

             }

         } while (true);

         // update the acceptable sequence value for this entry

         io_value = pBuffer[readPos & uQueueIndexMask].value;

         AkAtomicStore64(&pBuffer[readPos & uQueueIndexMask].uSequence, readPos + m_uQueueIndexMask + 1);

         return true;

     }

     /// Checks if there is a value available to be dequeued

     bool Empty()

     {

         AkInt64 readPos = AkAtomicLoad64(&m_readPos);

         AkInt64 sequenceDelta = AkAtomicLoad64(&m_buffer[readPos & m_uQueueIndexMask].uSequence) - (readPos + 1);

         return sequenceDelta < 0;

     }

 private:

     struct FifoQueueEntry

     {

         // Value actually contained in the queue

         T value;

         // Global index of the queue entry in the sequence, to detect when we are at a valid read or write pos

         AkAtomic64 uSequence;

     };

     // Buffer of QueueEntries

     FifoQueueEntry* m_buffer;

     // Mask to apply to the read/write position to clamp it to array bounds

     AkInt64 m_uQueueIndexMask;

     // readIndex of where we are in the sequence

     AkAtomic64 m_readPos;

     // writeIndex of where we are in the sequence

     AkAtomic64 m_writePos;

 };

 #endif // _AKFIFOQUEUE_H