// ==++==
//
//   Copyright (c) Microsoft Corporation.  All rights reserved.
//
// ==--==
//=============================================================================
//
// Class: LocalDataStoreMgr
//
// Purpose: Class that manages stores of local data. This class is used in
//          cooperation with the LocalDataStore class.
//
//=============================================================================  
namespace System
{

    using System;
    using System.Collections;

    // This is a cheesy internal helper class that is used to make sure memory
    // is actually being accessed and not some cached copy of a field in a
    // register.
    // WARNING: If we every do type analysis to eliminate virtual functions,
    // this will break.
    internal class LdsSyncHelper
    {
        internal virtual int Get(ref int slot)
        {
            return slot;
        }
    }

    // This class is an encapsulation of a slot so that it is managed in a secure fashion.
    // It is constructed by the LocalDataStoreManager, holds the slot and the manager
    // and cleans up when it is finalized.
    //| <include path='docs/doc[@for="LocalDataStoreSlot"]/*' />
    public sealed class LocalDataStoreSlot
    {
        private static LdsSyncHelper m_helper = new LdsSyncHelper();

        private LocalDataStoreMgr m_mgr;
        private int m_slot;

        // Construct the object to encapsulate the slot.
        internal LocalDataStoreSlot(LocalDataStoreMgr mgr, int slot)
        {
            m_mgr = mgr;
            m_slot = slot;
        }

        // Accessors for the two fields of this class.
        internal LocalDataStoreMgr Manager
        {
            get
            {
                return m_mgr;
            }
        }
        internal int Slot
        {
            get
            {
                return m_slot;
            }
        }

        // This is used to make sure we are actually reading and writing to
        // memory to fetch the slot (rather than possibly using a value
        // cached in a register).
        internal bool IsValid()
        {
            return m_helper.Get(ref m_slot) != -1;
        }

        // Release the slot reserved by this object when this object goes away.
        // There is  a race condition that can happen in the face of
        // resurrection where another thread is fetching values or assigning
        // while the finalizer thread is here.  We are counting on the fact
        // that code that fetches values calls IsValid after fetching a value
        // and before giving it to anyone.  See LocalDataStore for the other
        // half of this.  We are also counting on code that sets values locks
        // the manager.
        //| <include path='docs/doc[@for="LocalDataStoreSlot.Finalize"]/*' />
        ~LocalDataStoreSlot()
        {
            int slot = m_slot;

            // This lock fixes synchronization with the assignment of values.
            lock (m_mgr) {
                // Mark the slot as free.
                m_slot = -1;

                m_mgr.FreeDataSlot(slot);
            }
        }
    }

    internal class LocalDataStoreMgr
    {
        private const byte DataSlotOccupied             = 0x01;

        private const int InitialSlotTableSize          = 64;
        private const int SlotTableDoubleThreshold      = 512;
        private const int LargeSlotTableSizeIncrease    = 128;

        //=========================================================================
        // Create a data store to be managed by this manager and add it to the
        // list. The initial size of the new store matches the number of slots
        // allocated in this manager.
        //=========================================================================  
        public LocalDataStore CreateLocalDataStore()
        {
            // Create a new local data store.
            LocalDataStore Store = new LocalDataStore(this, m_SlotInfoTable.Length);

            lock (this) {
                // Add the store to the array list and return it.
                m_ManagedLocalDataStores.Add(Store);
            }
            return Store;
        }

        //=========================================================================
        // Remove the specified store from the list of managed stores..
        //=========================================================================  
        public void DeleteLocalDataStore(LocalDataStore store)
        {
            lock (this) {
                // Remove the store to the array list and return it.
                m_ManagedLocalDataStores.Remove(store);
            }
        }

        //=========================================================================
        // Allocates a data slot by finding an available index and wrapping it
        // an object to prevent clients from manipulating it directly, allowing us
        // to make assumptions its integrity.
        //=========================================================================  
        public LocalDataStoreSlot AllocateDataSlot()
        {
            lock (this) {
                int i;
                LocalDataStoreSlot slot;

                // Retrieve the current size of the table.
                int SlotTableSize = m_SlotInfoTable.Length;

                // Check if there are any slots left.
                if (m_FirstAvailableSlot < SlotTableSize) {
                    // Save the first available slot.
                    slot = new LocalDataStoreSlot(this, m_FirstAvailableSlot);
                    m_SlotInfoTable[m_FirstAvailableSlot] = DataSlotOccupied;

                    // Find the next available slot.
                    for (i = m_FirstAvailableSlot + 1; i < SlotTableSize; ++i)
                        if (0 == (m_SlotInfoTable[i] & DataSlotOccupied))
                            break;

                    // Save the new "first available slot".
                    m_FirstAvailableSlot = i;

                    // Return the slot index.
                    return slot;
                }

                // The table is full so we need to increase its size.
                int NewSlotTableSize;
                if (SlotTableSize < SlotTableDoubleThreshold) {
                    // The table is still relatively small so double it.
                    NewSlotTableSize = SlotTableSize * 2;
                }
                else {
                    // The table is relatively large so simply increase its size by a given amount.
                    NewSlotTableSize = SlotTableSize + LargeSlotTableSizeIncrease;
                }

                // Allocate the new slot info table.
                byte[] NewSlotInfoTable = new byte[NewSlotTableSize];

                // Copy the old array into the new one.
                Array.Copy(m_SlotInfoTable, NewSlotInfoTable, SlotTableSize);
                m_SlotInfoTable = NewSlotInfoTable;

                // SlotTableSize is the index of the first empty slot in the expanded table.
                slot = new LocalDataStoreSlot(this, SlotTableSize);
                m_SlotInfoTable[SlotTableSize] = DataSlotOccupied;
                m_FirstAvailableSlot = SlotTableSize + 1;

                // Return the selected slot
                return slot;
            }
        }

        //=========================================================================
        // Allocate a slot and associate a name with it.
        //=========================================================================  
        public LocalDataStoreSlot AllocateNamedDataSlot(String name)
        {
            lock (this) {
                // Allocate a normal data slot.
                LocalDataStoreSlot slot = AllocateDataSlot();

                // Insert the association between the name and the data slot number
                // in the hash table.
                m_KeyToSlotMap.Add(name, slot);
                return slot;
            }
        }

        //=========================================================================
        // Retrieve the slot associated with a name, allocating it if no such
        // association has been defined.
        //=========================================================================  
        public LocalDataStoreSlot GetNamedDataSlot(String name)
        {
            lock (this) {
                // Lookup in the hashtable to try find a slot for the name.
                LocalDataStoreSlot slot = (LocalDataStoreSlot) m_KeyToSlotMap[name];

                // If the name is not yet in the hashtable then add it.
                if (null == slot)
                    return AllocateNamedDataSlot(name);

                // The name was in the hashtable so return the associated slot.
                return slot;
            }
        }

        //=========================================================================
        // Eliminate the association of a name with a slot.  The actual slot will
        // be reclaimed when the finalizer for the slot object runs.
        //=========================================================================  
        public void FreeNamedDataSlot(String name)
        {
            lock (this) {
                // Remove the name slot association from the hashtable.
                m_KeyToSlotMap.Remove(name);
            }
        }

        //=========================================================================
        // Free's a previously allocated data slot on ALL the managed data stores.
        //=========================================================================  
        internal void FreeDataSlot(int slot)
        {
            lock (this) {
                // Go thru all the managed stores and set the data on the specified slot to 0.
                for (int i = 0; i < m_ManagedLocalDataStores.Count; i++) {
                    ((LocalDataStore)m_ManagedLocalDataStores[i]).SetDataInternal(
                                                                      slot,
                                                                      null,
                                                                      false);
                }

                // Mark the slot as being no longer occupied.
                m_SlotInfoTable[slot] = 0;
                if (slot < m_FirstAvailableSlot)
                    m_FirstAvailableSlot = slot;
            }
        }

        //=========================================================================
        // Return the number of allocated slots in this manager.
        //=========================================================================  
        public void ValidateSlot(LocalDataStoreSlot slot)
        {
            // Make sure the slot was allocated for this store.
            if (slot == null || slot.Manager != this)
                throw new ArgumentException("Argument_ALSInvalidSlot");
        }

        //=========================================================================
        // Return the number of allocated slots in this manager.
        //=========================================================================  
        internal int GetSlotTableLength()
        {
                return m_SlotInfoTable.Length;
        }

        private byte[] m_SlotInfoTable = new byte[InitialSlotTableSize];
        private int m_FirstAvailableSlot = 0;
        private ArrayList m_ManagedLocalDataStores = new ArrayList();
        private Hashtable m_KeyToSlotMap = new Hashtable();
    }
}