src/core/lib/slice/slice_hash_table.c

//
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#include "src/core/lib/slice/slice_hash_table.h"

#include <stdbool.h>
#include <string.h>

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

#include "src/core/lib/slice/slice_internal.h"
#include "src/core/lib/transport/metadata.h"

struct grpc_slice_hash_table {
  gpr_refcount refs;
  size_t size;
  grpc_slice_hash_table_entry* entries;
};

static bool is_empty(grpc_slice_hash_table_entry* entry) {
  return entry->vtable == NULL;
}

// Helper function for insert and get operations that performs quadratic
// probing (https://en.wikipedia.org/wiki/Quadratic_probing).
static size_t grpc_slice_hash_table_find_index(
    const grpc_slice_hash_table* table, const grpc_slice key, bool find_empty) {
  size_t hash = grpc_slice_hash(key);
  for (size_t i = 0; i < table->size; ++i) {
    const size_t idx = (hash + i * i) % table->size;
    if (is_empty(&table->entries[idx])) {
      return find_empty ? idx : table->size;
    }
    if (grpc_slice_eq(table->entries[idx].key, key)) {
      return idx;
    }
  }
  return table->size;  // Not found.
}

static void grpc_slice_hash_table_add(
    grpc_slice_hash_table* table, grpc_slice key, void* value,
    const grpc_slice_hash_table_vtable* vtable) {
  GPR_ASSERT(value != NULL);
  const size_t idx =
      grpc_slice_hash_table_find_index(table, key, true /* find_empty */);
  GPR_ASSERT(idx != table->size);  // Table should never be full.
  grpc_slice_hash_table_entry* entry = &table->entries[idx];
  entry->key = grpc_slice_ref_internal(key);
  entry->value = vtable->copy_value(value);
  entry->vtable = vtable;
}

grpc_slice_hash_table* grpc_slice_hash_table_create(
    size_t num_entries, grpc_slice_hash_table_entry* entries) {
  grpc_slice_hash_table* table = gpr_zalloc(sizeof(*table));
  gpr_ref_init(&table->refs, 1);
  // Quadratic probing gets best performance when the table is no more
  // than half full.
  table->size = num_entries * 2;
  const size_t entry_size = sizeof(grpc_slice_hash_table_entry) * table->size;
  table->entries = gpr_zalloc(entry_size);
  for (size_t i = 0; i < num_entries; ++i) {
    grpc_slice_hash_table_entry* entry = &entries[i];
    grpc_slice_hash_table_add(table, entry->key, entry->value, entry->vtable);
  }
  return table;
}

grpc_slice_hash_table* grpc_slice_hash_table_ref(grpc_slice_hash_table* table) {
  if (table != NULL) gpr_ref(&table->refs);
  return table;
}

void grpc_slice_hash_table_unref(grpc_exec_ctx* exec_ctx,
                                 grpc_slice_hash_table* table) {
  if (table != NULL && gpr_unref(&table->refs)) {
    for (size_t i = 0; i < table->size; ++i) {
      grpc_slice_hash_table_entry* entry = &table->entries[i];
      if (!is_empty(entry)) {
        grpc_slice_unref_internal(exec_ctx, entry->key);
        entry->vtable->destroy_value(exec_ctx, entry->value);
      }
    }
    gpr_free(table->entries);
    gpr_free(table);
  }
}

void* grpc_slice_hash_table_get(const grpc_slice_hash_table* table,
                                const grpc_slice key) {
  const size_t idx =
      grpc_slice_hash_table_find_index(table, key, false /* find_empty */);
  if (idx == table->size) return NULL;  // Not found.
  return table->entries[idx].value;
}