#ifndef Py_INTERNAL_INDEX_POOL_H
#define Py_INTERNAL_INDEX_POOL_H

#include "Python.h"

#ifdef __cplusplus
extern "C" {
#endif

#ifndef Py_BUILD_CORE
#  error "this header requires Py_BUILD_CORE define"
#endif

#ifdef Py_GIL_DISABLED

// This contains code for allocating unique indices in an array. It is used by
// the free-threaded build to assign each thread a globally unique index into
// each code object's thread-local bytecode array.

// A min-heap of indices
typedef struct _PyIndexHeap {
    int32_t *values;

    // Number of items stored in values
    Py_ssize_t size;

    // Maximum number of items that can be stored in values
    Py_ssize_t capacity;
} _PyIndexHeap;

// An unbounded pool of indices. Indices are allocated starting from 0. They
// may be released back to the pool once they are no longer in use.
typedef struct _PyIndexPool {
    PyMutex mutex;

    // Min heap of indices available for allocation
    _PyIndexHeap free_indices;

    // Next index to allocate if no free indices are available
    int32_t next_index;
} _PyIndexPool;

// Allocate the smallest available index. Returns -1 on error.
extern int32_t _PyIndexPool_AllocIndex(_PyIndexPool *indices);

// Release `index` back to the pool
extern void _PyIndexPool_FreeIndex(_PyIndexPool *indices, int32_t index);

extern void _PyIndexPool_Fini(_PyIndexPool *indices);

#endif // Py_GIL_DISABLED

#ifdef __cplusplus
}
#endif
#endif // !Py_INTERNAL_INDEX_POOL_H