/*
 *
 * Copyright 2017 gRPC authors.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 */

#include <grpc/support/port_platform.h>

#include "src/core/lib/gpr/arena.h"

#include <string.h>

#include <grpc/support/alloc.h>
#include <grpc/support/atm.h>
#include <grpc/support/log.h>
#include <grpc/support/sync.h>

#include "src/core/lib/gpr/alloc.h"

// Uncomment this to use a simple arena that simply allocates the
// requested amount of memory for each call to gpr_arena_alloc().  This
// effectively eliminates the efficiency gain of using an arena, but it
// may be useful for debugging purposes.
//#define SIMPLE_ARENA_FOR_DEBUGGING

#ifdef SIMPLE_ARENA_FOR_DEBUGGING

struct gpr_arena {
  gpr_mu mu;
  void** ptrs;
  size_t num_ptrs;
};

gpr_arena* gpr_arena_create(size_t ignored_initial_size) {
  gpr_arena* arena = (gpr_arena*)gpr_zalloc(sizeof(*arena));
  gpr_mu_init(&arena->mu);
  return arena;
}

size_t gpr_arena_destroy(gpr_arena* arena) {
  gpr_mu_destroy(&arena->mu);
  for (size_t i = 0; i < arena->num_ptrs; ++i) {
    gpr_free(arena->ptrs[i]);
  }
  gpr_free(arena->ptrs);
  gpr_free(arena);
  return 1;  // Value doesn't matter, since it won't be used.
}

void* gpr_arena_alloc(gpr_arena* arena, size_t size) {
  gpr_mu_lock(&arena->mu);
  arena->ptrs =
      (void**)gpr_realloc(arena->ptrs, sizeof(void*) * (arena->num_ptrs + 1));
  void* retval = arena->ptrs[arena->num_ptrs++] = gpr_zalloc(size);
  gpr_mu_unlock(&arena->mu);
  return retval;
}

#else  // SIMPLE_ARENA_FOR_DEBUGGING

// TODO(roth): We currently assume that all callers need alignment of 16
// bytes, which may be wrong in some cases.  As part of converting the
// arena API to C++, we should consider replacing gpr_arena_alloc() with a
// template that takes the type of the value being allocated, which
// would allow us to use the alignment actually needed by the caller.

typedef struct zone {
  zone* next;
} zone;

struct gpr_arena {
  // Keep track of the total used size. We use this in our call sizing
  // historesis.
  gpr_atm total_used;
  size_t initial_zone_size;
  zone initial_zone;
  zone* last_zone;
  gpr_mu arena_growth_mutex;
};

static void* zalloc_aligned(size_t size) {
  void* ptr = gpr_malloc_aligned(size, GPR_MAX_ALIGNMENT);
  memset(ptr, 0, size);
  return ptr;
}

gpr_arena* gpr_arena_create(size_t initial_size) {
  initial_size = GPR_ROUND_UP_TO_ALIGNMENT_SIZE(initial_size);
  gpr_arena* a = static_cast<gpr_arena*>(zalloc_aligned(
      GPR_ROUND_UP_TO_ALIGNMENT_SIZE(sizeof(gpr_arena)) + initial_size));
  a->initial_zone_size = initial_size;
  a->last_zone = &a->initial_zone;
  gpr_mu_init(&a->arena_growth_mutex);
  return a;
}

size_t gpr_arena_destroy(gpr_arena* arena) {
  gpr_mu_destroy(&arena->arena_growth_mutex);
  gpr_atm size = gpr_atm_no_barrier_load(&arena->total_used);
  zone* z = arena->initial_zone.next;
  gpr_free_aligned(arena);
  while (z) {
    zone* next_z = z->next;
    gpr_free_aligned(z);
    z = next_z;
  }
  return static_cast<size_t>(size);
}

void* gpr_arena_alloc(gpr_arena* arena, size_t size) {
  size = GPR_ROUND_UP_TO_ALIGNMENT_SIZE(size);
  size_t begin = gpr_atm_no_barrier_fetch_add(&arena->total_used, size);
  if (begin + size <= arena->initial_zone_size) {
    return reinterpret_cast<char*>(arena) +
           GPR_ROUND_UP_TO_ALIGNMENT_SIZE(sizeof(gpr_arena)) + begin;
  } else {
    // If the allocation isn't able to end in the initial zone, create a new
    // zone for this allocation, and any unused space in the initial zone is
    // wasted. This overflowing and wasting is uncommon because of our arena
    // sizing historesis (that is, most calls should have a large enough initial
    // zone and will not need to grow the arena).
    gpr_mu_lock(&arena->arena_growth_mutex);
    zone* z = static_cast<zone*>(
        zalloc_aligned(GPR_ROUND_UP_TO_ALIGNMENT_SIZE(sizeof(zone)) + size));
    arena->last_zone->next = z;
    arena->last_zone = z;
    gpr_mu_unlock(&arena->arena_growth_mutex);
    return reinterpret_cast<char*>(z) +
           GPR_ROUND_UP_TO_ALIGNMENT_SIZE(sizeof(zone));
  }
}

#endif  // SIMPLE_ARENA_FOR_DEBUGGING