/* ----------------------------------------------------------------------------
Copyright (c) 2019, Microsoft Research, Daan Leijen
This is free software; you can redistribute it and/or modify it under the
terms of the MIT license. A copy of the license can be found in the file
"LICENSE" at the root of this distribution.
-----------------------------------------------------------------------------*/

/* ----------------------------------------------------------------------------

-----------------------------------------------------------------------------*/
#include "mimalloc.h"
#include "mimalloc-internal.h"
#include "mimalloc-atomic.h"

#include <string.h>  // memset

/* -----------------------------------------------------------
  Arena allocation
----------------------------------------------------------- */

#define MI_SEGMENT_ALIGN     MI_SEGMENT_SIZE
#define MI_ARENA_BLOCK_SIZE  MI_SEGMENT_SIZE 
#define MI_MAX_ARENAS        (64)

// Block info: bit 0 contains the `in_use` bit, the upper bits the
// size in count of arena blocks.
typedef uintptr_t mi_block_info_t;

// A memory arena descriptor
typedef struct mi_arena_s {
  uint8_t* start;                         // the start of the memory area
  size_t   block_count;                   // size of the area in arena blocks (of `MI_ARENA_BLOCK_SIZE`)
  bool     is_zero_init;                  // is the arena zero initialized?
  bool     is_large;                      // large OS page allocated
  _Atomic(uintptr_t)       block_bottom;  // optimization to start the search for free blocks
  _Atomic(mi_block_info_t) blocks[1];     // `block_count` block info's
} mi_arena_t;


// The available arenas
static _Atomic(mi_arena_t*) mi_arenas[MI_MAX_ARENAS];
static _Atomic(uintptr_t)   mi_arena_count; // = 0


/* -----------------------------------------------------------
  Arena allocations get a memory id where the lower 8 bits are
  the arena index +1, and the upper bits the block index.
----------------------------------------------------------- */

// Use `SIZE_MAX` as a special id for direct OS allocated memory.
#define MI_MEMID_OS   (SIZE_MAX)

static size_t mi_memid_create(size_t arena_index, size_t block_index) {
  mi_assert_internal(arena_index < 0xFE);
  return ((block_index << 8) | ((arena_index+1) & 0xFF));
}

static void mi_memid_indices(size_t memid, size_t* arena_index, size_t* block_index) {
  mi_assert_internal(memid != MI_MEMID_OS);
  mi_assert_internal(memid != 0);
  *arena_index = (memid & 0xFF) - 1;
  *block_index = (memid >> 8);
}

/* -----------------------------------------------------------
  Block info
----------------------------------------------------------- */

static bool mi_block_is_in_use(mi_block_info_t info) {
  return ((info&1) != 0);
}

static size_t mi_block_count(mi_block_info_t info) {
  return (info>>1);
}

static mi_block_info_t mi_block_info_create(size_t bcount, bool in_use) {
  return (((mi_block_info_t)bcount << 1) | (in_use ? 1 : 0));
}


/* -----------------------------------------------------------
  Thread safe allocation in an arena
----------------------------------------------------------- */

static void* mi_arena_allocx(mi_arena_t* arena, size_t start_idx, size_t end_idx, size_t needed_bcount, bool* is_zero, size_t* block_index)
{
  // Scan linearly through all block info's
  // Skipping used ranges, coalescing free ranges on demand.
  mi_assert_internal(needed_bcount > 0);
  mi_assert_internal(start_idx <= arena->block_count);
  mi_assert_internal(end_idx <= arena->block_count);
  _Atomic(mi_block_info_t)* block = &arena->blocks[start_idx];
  _Atomic(mi_block_info_t)* end = &arena->blocks[end_idx];
  while (block < end) {
    mi_block_info_t binfo = mi_atomic_read_relaxed(block);
    size_t bcount = mi_block_count(binfo);
    if (mi_block_is_in_use(binfo)) {
      // in-use, skip ahead
      mi_assert_internal(bcount > 0);
      block += bcount;
    }
    else {
      // free blocks
      if (bcount==0) {
        // optimization:
        // use 0 initialized blocks at the end, to use single atomic operation
        // initially to reduce contention (as we don't need to split)
        if (block + needed_bcount > end) {
          return NULL; // does not fit
        }
        else if (!mi_atomic_cas_weak(block, mi_block_info_create(needed_bcount, true), binfo)) {
          // ouch, someone else was quicker. Try again..
          continue;
        }
        else {
          // we got it: return a pointer to the claimed memory
          ptrdiff_t idx = (block - arena->blocks);
          *is_zero = arena->is_zero_init;
          *block_index = idx;
          return (arena->start + (idx*MI_ARENA_BLOCK_SIZE));
        }
      }

      mi_assert_internal(bcount>0);
      if (needed_bcount > bcount) {
#if 0 // MI_NO_ARENA_COALESCE
        block += bcount; // too small, skip to the next range
        continue;
#else
        // too small, try to coalesce
        _Atomic(mi_block_info_t)* block_next = block + bcount;
        if (block_next >= end) {
          return NULL; // does not fit
        }
        mi_block_info_t binfo_next = mi_atomic_read(block_next);
        size_t bcount_next = mi_block_count(binfo_next);
        if (mi_block_is_in_use(binfo_next)) {
          // next block is in use, cannot coalesce
          block += (bcount + bcount_next); // skip ahea over both blocks
        }
        else {
          // next block is free, try to coalesce
          // first set the next one to being used to prevent dangling ranges
          if (!mi_atomic_cas_strong(block_next, mi_block_info_create(bcount_next, true), binfo_next)) {
            // someone else got in before us.. try again
            continue;
          }
          else {
            if (!mi_atomic_cas_strong(block, mi_block_info_create(bcount + bcount_next, true), binfo)) {  // use strong to increase success chance
              // someone claimed/coalesced the block in the meantime
              // first free the next block again..
              bool ok = mi_atomic_cas_strong(block_next, mi_block_info_create(bcount_next, false), binfo_next); // must be strong
              mi_assert(ok); UNUSED(ok);
              // and try again
              continue;
            }
            else {
              // coalesced! try again
              // todo: we could optimize here to immediately claim the block if the
              // coalesced size is a fit instead of retrying. Keep it simple for now.
              continue;
            }
          }
        }
#endif    
      }
      else {  // needed_bcount <= bcount
        mi_assert_internal(needed_bcount <= bcount);
        // it fits, claim the whole block
        if (!mi_atomic_cas_weak(block, mi_block_info_create(bcount, true), binfo)) {
          // ouch, someone else was quicker. Try again..
          continue;
        }
        else {
          // got it, now split off the needed part          
          if (needed_bcount < bcount) {
            mi_atomic_write(block + needed_bcount, mi_block_info_create(bcount - needed_bcount, false));
            mi_atomic_write(block, mi_block_info_create(needed_bcount, true));
          }
          // return a pointer to the claimed memory
          ptrdiff_t idx = (block - arena->blocks);
          *is_zero = false;
          *block_index = idx;
          return (arena->start + (idx*MI_ARENA_BLOCK_SIZE));
        }
      }
    }
  }
  // no success
  return NULL;
}

// Try to reduce search time by starting from bottom and wrap around.
static void* mi_arena_alloc(mi_arena_t* arena, size_t needed_bcount, bool* is_zero, size_t* block_index) 
{
  uintptr_t bottom = mi_atomic_read_relaxed(&arena->block_bottom);
  void* p = mi_arena_allocx(arena, bottom, arena->block_count, needed_bcount, is_zero, block_index);
  if (p == NULL && bottom > 0) {
    // try again from the start
    p = mi_arena_allocx(arena, 0, bottom, needed_bcount, is_zero, block_index);
  }
  if (p != NULL) {
    mi_atomic_write(&arena->block_bottom, *block_index);
  }
  return p;
}

/* -----------------------------------------------------------
  Arena Allocation
----------------------------------------------------------- */

void* _mi_arena_alloc_aligned(size_t size, size_t alignment, bool* commit, bool* large, bool* is_zero, size_t* memid, mi_os_tld_t* tld) {
  mi_assert_internal(memid != NULL && tld != NULL);
  mi_assert_internal(size > 0);
  *memid = MI_MEMID_OS;  
  *is_zero = false;
  bool default_large = false;
  if (large==NULL) large = &default_large;  // ensure `large != NULL`

  // try to allocate in an arena if the alignment is small enough
  // and if there is not too much waste around the `MI_ARENA_BLOCK_SIZE`.
  if (alignment <= MI_SEGMENT_ALIGN &&
      size >= 3*(MI_ARENA_BLOCK_SIZE/4) &&  // > 48MiB (not more than 25% waste)
      !(size > MI_ARENA_BLOCK_SIZE && size < 3*(MI_ARENA_BLOCK_SIZE/2)) // ! <64MiB - 96MiB>
     ) 
  {
    size_t asize = _mi_align_up(size, MI_ARENA_BLOCK_SIZE);
    size_t bcount = asize / MI_ARENA_BLOCK_SIZE;

    mi_assert_internal(size <= bcount*MI_ARENA_BLOCK_SIZE);
    for (size_t i = 0; i < MI_MAX_ARENAS; i++) {
      mi_arena_t* arena = (mi_arena_t*)mi_atomic_read_ptr_relaxed(mi_atomic_cast(void*, &mi_arenas[i]));
      if (arena==NULL) break;
      size_t block_index = SIZE_MAX;
      void* p = mi_arena_alloc(arena, bcount, is_zero, &block_index);
      if (p != NULL) {
        mi_assert_internal(block_index != SIZE_MAX);
        #if MI_DEBUG>=1
        _Atomic(mi_block_info_t)* block = &arena->blocks[block_index];
        mi_block_info_t binfo = mi_atomic_read(block);
        mi_assert_internal(mi_block_is_in_use(binfo));
        mi_assert_internal(mi_block_count(binfo)*MI_ARENA_BLOCK_SIZE >= size);
        #endif 
        *memid = mi_memid_create(i, block_index);
        *commit = true;           // TODO: support commit on demand?
        *large = arena->is_large;
        mi_assert_internal((uintptr_t)p % alignment == 0);
        return p;
      }
    }
  }

  // fall back to the OS
  *is_zero = true;
  *memid = MI_MEMID_OS;
  return _mi_os_alloc_aligned(size, alignment, *commit, large, tld);
}

void* _mi_arena_alloc(size_t size, bool* commit, bool* large, bool* is_zero, size_t* memid, mi_os_tld_t* tld) 
{
  return _mi_arena_alloc_aligned(size, MI_ARENA_BLOCK_SIZE, commit, large, is_zero, memid, tld);
}

/* -----------------------------------------------------------
  Arena free
----------------------------------------------------------- */

void _mi_arena_free(void* p, size_t size, size_t memid, mi_stats_t* stats) {
  mi_assert_internal(size > 0 && stats != NULL);
  if (p==NULL) return;
  if (size==0) return;
  if (memid == MI_MEMID_OS) {
    // was a direct OS allocation, pass through
    _mi_os_free(p, size, stats);
  }
  else {
    mi_assert_internal(memid != 0);
    // allocated in an arena
    size_t arena_idx;
    size_t block_idx;
    mi_memid_indices(memid, &arena_idx, &block_idx);
    mi_assert_internal(arena_idx < MI_MAX_ARENAS);
    mi_arena_t* arena = (mi_arena_t*)mi_atomic_read_ptr_relaxed(mi_atomic_cast(void*, &mi_arenas[arena_idx]));
    mi_assert_internal(arena != NULL);
    if (arena == NULL) {
      _mi_fatal_error("trying to free from non-existent arena: %p, size %zu, memid: 0x%zx\n", p, size, memid);
      return;
    }
    mi_assert_internal(arena->block_count > block_idx);
    if (arena->block_count <= block_idx) {
      _mi_fatal_error("trying to free from non-existent block: %p, size %zu, memid: 0x%zx\n", p, size, memid);
      return;
    }
    _Atomic(mi_block_info_t)* block = &arena->blocks[block_idx];
    mi_block_info_t binfo = mi_atomic_read_relaxed(block);
    mi_assert_internal(mi_block_is_in_use(binfo));
    mi_assert_internal(mi_block_count(binfo)*MI_ARENA_BLOCK_SIZE >= size);
    if (!mi_block_is_in_use(binfo)) {
      _mi_fatal_error("trying to free an already freed block: %p, size %zu\n", p, size);
      return;
    };
    bool ok = mi_atomic_cas_strong(block, mi_block_info_create(mi_block_count(binfo), false), binfo);
    mi_assert_internal(ok);
    if (!ok) {
      _mi_warning_message("unable to free arena block: %p, info 0x%zx", p, binfo);
    }
    if (block_idx < mi_atomic_read_relaxed(&arena->block_bottom)) {
      mi_atomic_write(&arena->block_bottom, block_idx);
    }
  }
}

/* -----------------------------------------------------------
  Add an arena.
----------------------------------------------------------- */

static bool mi_arena_add(mi_arena_t* arena) {
  mi_assert_internal(arena != NULL);
  mi_assert_internal((uintptr_t)arena->start % MI_SEGMENT_ALIGN == 0);
  mi_assert_internal(arena->block_count > 0);
  mi_assert_internal(mi_mem_is_zero(arena->blocks,arena->block_count*sizeof(mi_block_info_t)));
  
  uintptr_t i = mi_atomic_addu(&mi_arena_count,1);
  if (i >= MI_MAX_ARENAS) {
    mi_atomic_subu(&mi_arena_count, 1);
    return false;
  }
  mi_atomic_write_ptr(mi_atomic_cast(void*,&mi_arenas[i]), arena);
  return true;
}


/* -----------------------------------------------------------
  Reserve a huge page arena.
  TODO: improve OS api to just reserve and claim a huge
  page area at once, (and return the total size).
----------------------------------------------------------- */

#include <errno.h>

void* _mi_os_try_alloc_from_huge_reserved(size_t size, size_t try_alignment);

int mi_reserve_huge_os_pages(size_t pages, double max_secs, size_t* pages_reserved) mi_attr_noexcept {
  size_t pages_reserved_default = 0;
  if (pages_reserved==NULL) pages_reserved = &pages_reserved_default;
  int err = _mi_os_reserve_huge_os_pages(pages, max_secs, pages_reserved);
  if (*pages_reserved==0) return err;
  size_t hsize = (*pages_reserved) * GiB;
  void* p = _mi_os_try_alloc_from_huge_reserved(hsize, MI_SEGMENT_ALIGN);
  mi_assert_internal(p != NULL);
  if (p == NULL) return ENOMEM;
  size_t bcount = hsize / MI_ARENA_BLOCK_SIZE;
  size_t asize = sizeof(mi_arena_t) + (bcount*sizeof(mi_block_info_t)); // one too much
  mi_arena_t* arena = (mi_arena_t*)_mi_os_alloc(asize, &_mi_heap_default->tld->stats);
  if (arena == NULL) return ENOMEM;
  arena->block_count = bcount;
  arena->start = (uint8_t*)p;
  arena->block_bottom = 0;
  arena->is_large = true;
  arena->is_zero_init = true;
  memset(arena->blocks, 0, bcount * sizeof(mi_block_info_t));
  //mi_atomic_write(&arena->blocks[0], mi_block_info_create(bcount, false));
  mi_arena_add(arena);
  return 0;
}