172 lines
6.1 KiB
C++
172 lines
6.1 KiB
C++
///////////////////////////////////////////////////////////////////
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//
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// THE ID ALLOCATOR
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//
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// This ID allocator's goal is to allocate IDs in such a way that the
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// synchronous model gets the same IDs as the master model.
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//
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// DESIGN PRINCIPLES
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//
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// There are two classes defined here: IdGlobalPool, and IdPlayerPool.
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//
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// Every logged-in player maintains an IdPlayerPool. That's basically a fifo
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// queue of ID batches. An ID batch is a contiguous range of IDs, containing
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// between 128 and 256 contiguous IDs. The IdPlayerPool is difference
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// transmitted, to ensure that the synchronous model has the same batches as the
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// master model.
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//
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// When a player creates a thread, that thread gets an ID batch from the
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// IdPlayerPool. To make this possible, the Lua runtime has been modified so
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// that a thread can contain an ID batch. When that thread allocates IDs, it
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// uses the batch it was allocated. In the unlikely event that a thread's batch
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// is used up, the thread falls back to using the IdGlobalPool. Such fallback
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// IDs are not likely to be predicted correctly.
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//
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// When a player creates a thread, he uses up one batch from his IdPlayerPool.
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// In the master model, the player pool is 'refilled' by asking the IdGlobalPool
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// to create a new batch. In the synchronous model, the IdPlayerPool is not
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// directly refilled, but the difference transmitter effectively refills it. It
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// is imperative that this difference transmission happen before the player's
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// asynchronous model runs out of batches, otherwise we'll get prediction
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// failures.
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//
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// It is common that a thread will only use 1 or 2 IDs. If a thread exits
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// without using up most of its IDs, then the batch it contains is still a
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// pretty usable batch. The batch gets returned to the IdGlobalPool, which will
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// eventually use that salvaged batch to satisfy an IdPlayerPool refill request.
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//
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// THE NUMERIC RANGES
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//
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// * 0x0000+ : reserved for future expansion.
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// * 0x0001+ : used by master model's IdGlobalPool to create batches.
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// * 0x0010+ : used by master model's IdGlobalPool to create individual IDs.
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// * 0x001E+ : used by sync model's IdGlobalPool to create individual IDs.
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//
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// BATCH REPRESENTATION
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//
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// A batch is represented as a 64-bit integer. The batch contains all IDs
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// starting with that integer, and incrementing, until the the two lowest digits
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// are 0x00.
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//
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// For example, consider the batch ID 0x11111111111111FC. That batch includes
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// these IDs:
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//
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// * 0x11111111111111FC
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// * 0x11111111111111FD
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// * 0x11111111111111FE
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// * 0x11111111111111FF
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//
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// But it does not include 0x1111111111111200.
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//
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// As a special case, the number 0 is used to indicate "invalid batch".
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//
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///////////////////////////////////////////////////////////////////
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#ifndef IDALLOC_HPP
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#define IDALLOC_HPP
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#include <cstdint>
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#include <vector>
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#include <deque>
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#include "luastack.hpp"
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#include "streambuffer.hpp"
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class IdGlobalPool {
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private:
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std::vector<int64_t> salvaged_;
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int64_t next_batch_;
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int64_t next_id_;
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int32_t queue_fill_;
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friend int unittests_idalloc(lua_State *L);
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public:
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// Construct and destroy global pools. Note that after constructing
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// a global pool, it is generally also necessary to initialize it
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// for Master or Synchronous operation using init_master or init_synch.
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// Any attempt to use a pool that hasn't been init_master or init_synch
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// will fail.
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IdGlobalPool();
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~IdGlobalPool();
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// Initialize the pool for use in a master model.
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void init_master(int qf);
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// Initialize the pool for use in a synchronous model.
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void init_synch(int qf);
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// Create a single unique ID. Ids allocated this way are
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// unlikely to be predicted correctly.
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int64_t get_one();
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// Obtain a batch of IDs from the global pool. In a master
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// model, the batch is guaranteed to contain at least 128 IDs.
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// In a synchronous model, the batch is always zero (invalid).
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int64_t get_batch();
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// When a player pool refills its fifo queue, it refills it
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// with this many batches.
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int queue_fill() const { return queue_fill_; }
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// Try to return the specified batch to the global pool.
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// The salvage operation quietly does nothing if the batch is
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// zero, or the batch contains fewer than 128 IDs.
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void salvage(int64_t batch);
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// Return the thread's batch to the global pool. If no batch
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// is present, that's okay. Set the thread's batch to zero (invalid).
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void salvage_thread(lua_State *L);
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// Allocate an ID for the specified thread. Uses the thread's
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// batch if possible. If not, fetches one ID from the global pool.
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int64_t alloc_id_for_thread(lua_State *L);
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// Serialize to or deserialize from a streambuffer.
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void serialize(StreamBuffer *sb);
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void deserialize(StreamBuffer *sb);
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};
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class IdPlayerPool {
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private:
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IdGlobalPool *global_;
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std::deque<int64_t> ranges_;
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friend int unittests_idalloc(lua_State *L);
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public:
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// Construct a player pool.
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// The Player pool stores a pointer to the global pool.
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IdPlayerPool(IdGlobalPool *igp);
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~IdPlayerPool();
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// Refill the fifo queue of batches from the global pool.
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void refill();
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// Return all batches to the global pool. Leave the fifo empty.
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void unqueue();
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// Discard all batches. This is only for unit testing.
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void purge();
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// Get a batch from the fifo. Also refills the fifo.
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int64_t get_batch();
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// Return the thread's batch to the global pool. If no batch
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// is present, that's okay. Set the thread's batch to zero (invalid).
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void salvage_thread(lua_State *L);
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// Fetch a batch from the fifo and install it in the thread.
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// If the thread already had a batch, the thread's previous batch
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// is returned to the global pool.
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void prepare_thread(lua_State *L);
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// Return the size of the queue.
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int size() { return ranges_.size(); }
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// Serialize to or deserialize from a streambuffer.
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// Caution: the pointer to the global pool is not serialized or deserialized.
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void serialize(StreamBuffer *sb);
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void deserialize(StreamBuffer *sb);
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};
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#endif // IDALLOC_HPP
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