src/core/lib/transport/mdstr_hash_table.c

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#include "src/core/lib/transport/mdstr_hash_table.h"

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

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

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

struct grpc_mdstr_hash_table {
  gpr_refcount refs;
  size_t num_entries;
  grpc_mdstr_hash_table_entry* entries;
};

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

static void grpc_mdstr_hash_table_add(
    grpc_mdstr_hash_table* table, grpc_mdstr* key, void* value,
    const grpc_mdstr_hash_table_vtable* vtable) {
  GPR_ASSERT(value != NULL);
  const size_t idx =
      grpc_mdstr_hash_table_find_index(table, key, true /* find_empty */);
  GPR_ASSERT(idx != table->num_entries);  // Table should never be full.
  grpc_mdstr_hash_table_entry* entry = &table->entries[idx];
  entry->key = GRPC_MDSTR_REF(key);
  entry->value = vtable->copy_value(value);
  entry->vtable = vtable;
}

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

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

int grpc_mdstr_hash_table_unref(grpc_mdstr_hash_table* table) {
  if (table != NULL && gpr_unref(&table->refs)) {
    for (size_t i = 0; i < table->num_entries; ++i) {
      grpc_mdstr_hash_table_entry* entry = &table->entries[i];
      if (entry->key != NULL) {
        GRPC_MDSTR_UNREF(entry->key);
        entry->vtable->destroy_value(entry->value);
      }
    }
    gpr_free(table->entries);
    gpr_free(table);
    return 1;
  }
  return 0;
}

void* grpc_mdstr_hash_table_get(const grpc_mdstr_hash_table* table,
                                const grpc_mdstr* key) {
  const size_t idx =
      grpc_mdstr_hash_table_find_index(table, key, false /* find_empty */);
  if (idx == table->num_entries) return NULL;  // Not found.
  return table->entries[idx].value;
}

int grpc_mdstr_hash_table_cmp(const grpc_mdstr_hash_table* table1,
                              const grpc_mdstr_hash_table* table2) {
  // Compare by num_entries.
  if (table1->num_entries < table2->num_entries) return -1;
  if (table1->num_entries > table2->num_entries) return 1;
  for (size_t i = 0; i < table1->num_entries; ++i) {
    grpc_mdstr_hash_table_entry* e1 = &table1->entries[i];
    grpc_mdstr_hash_table_entry* e2 = &table2->entries[i];
    // Compare keys by hash value.
    if (e1->key->hash < e2->key->hash) return -1;
    if (e1->key->hash > e2->key->hash) return 1;
    // Compare by vtable (pointer equality).
    if (e1->vtable < e2->vtable) return -1;
    if (e1->vtable > e2->vtable) return 1;
    // Compare values via vtable.
    const int value_result = e1->vtable->compare_value(e1->value, e2->value);
    if (value_result != 0) return value_result;
  }
  return 0;
}