1 files changed, 136 insertions, 0 deletions

diff --git a/tests/t_mutex.c b/tests/t_mutex.c
new file mode 100644
index 0000000..e54e2fa
--- /dev/null
+++ b/tests/t_mutex.c
@@ -0,0 +1,136 @@
+/* This software was written by Dirk Engling <erdgeist@erdgeist.org>
+   It is considered beerware. Prost. Skol. Cheers or whatever. */
+
+/* System */
+#include <pthread.h>
+#include <stdatomic.h>
+#include <string.h>
+#include <unistd.h>
+
+/* Opentracker */
+#include "ot_mutex.h"
+#include "test.h"
+
+/* Every announce passes through here, and what it has to get right is which
+   bucket a hash belongs to and that two threads never hold one bucket at
+   once. Both are checked against real mutexes rather than a stand-in. */
+
+/* A hash that lands in a chosen bucket: the bucket is the top
+   OT_BUCKET_COUNT_BITS of the first four bytes, read in network order */
+static void hash_for_bucket(ot_hash hash, int bucket) {
+  memset(hash, 0, sizeof(ot_hash));
+  hash[0] = (uint8_t)(bucket >> (OT_BUCKET_COUNT_BITS - 8));
+  hash[1] = (uint8_t)((bucket << (16 - OT_BUCKET_COUNT_BITS)) & 0xff);
+}
+
+static void case_a_hash_names_its_bucket(void) {
+  static const int buckets[] = {0, 1, 2, 17, 511, 512, OT_BUCKET_COUNT - 1};
+  size_t           i;
+
+  test_case("a hash is served by the bucket its leading bits name");
+  for (i = 0; i < sizeof(buckets) / sizeof(buckets[0]); ++i) {
+    ot_hash    hash;
+    ot_vector *by_hash, *by_number;
+
+    hash_for_bucket(hash, buckets[i]);
+    by_hash = mutex_bucket_lock_by_hash(hash);
+    mutex_bucket_unlock_by_hash(hash, 0);
+
+    by_number = mutex_bucket_lock(buckets[i]);
+    mutex_bucket_unlock(buckets[i], 0);
+
+    CHECK(by_hash == by_number);
+  }
+}
+
+static void case_every_bucket_is_its_own(void) {
+  ot_vector *first, *last, *middle;
+
+  test_case("no two buckets are the same one");
+  first  = mutex_bucket_lock(0);
+  mutex_bucket_unlock(0, 0);
+  middle = mutex_bucket_lock(OT_BUCKET_COUNT / 2);
+  mutex_bucket_unlock(OT_BUCKET_COUNT / 2, 0);
+  last   = mutex_bucket_lock(OT_BUCKET_COUNT - 1);
+  mutex_bucket_unlock(OT_BUCKET_COUNT - 1, 0);
+
+  CHECK(first != middle);
+  CHECK(middle != last);
+  CHECK(first != last);
+}
+
+static void case_the_count_follows_what_unlock_is_told(void) {
+  size_t before = mutex_get_torrent_count();
+
+  test_case("the torrent count moves by what unlocking reports, and not otherwise");
+  mutex_bucket_lock(3);
+  mutex_bucket_unlock(3, 0);
+  CHECK_INT((int)(mutex_get_torrent_count() - before), 0);
+
+  mutex_bucket_lock(3);
+  mutex_bucket_unlock(3, 5);
+  CHECK_INT((int)(mutex_get_torrent_count() - before), 5);
+
+  mutex_bucket_lock(3);
+  mutex_bucket_unlock(3, -2);
+  CHECK_INT((int)(mutex_get_torrent_count() - before), 3);
+}
+
+static _Atomic int g_other_got_in;
+
+static void *take_a_bucket(void *args) {
+  int bucket = (int)(intptr_t)args;
+
+  mutex_bucket_lock(bucket);
+  atomic_store(&g_other_got_in, 1);
+  mutex_bucket_unlock(bucket, 0);
+  return NULL;
+}
+
+static int waited_for_entry(int patience_ms) {
+  int waited;
+
+  for (waited = 0; waited < patience_ms && !atomic_load(&g_other_got_in); ++waited)
+    usleep(1000);
+  return atomic_load(&g_other_got_in);
+}
+
+static void case_a_held_bucket_keeps_others_out(void) {
+  pthread_t other;
+
+  test_case("a second thread waits for the bucket this one holds");
+  atomic_store(&g_other_got_in, 0);
+  mutex_bucket_lock(9);
+  CHECK_INT(pthread_create(&other, NULL, take_a_bucket, (void *)(intptr_t)9), 0);
+
+  CHECK_INT(waited_for_entry(200), 0);
+
+  mutex_bucket_unlock(9, 0);
+  CHECK_INT(waited_for_entry(2000), 1);
+  pthread_join(other, NULL);
+}
+
+static void case_another_bucket_is_free_meanwhile(void) {
+  pthread_t other;
+
+  test_case("and a different bucket is not held up by it");
+  atomic_store(&g_other_got_in, 0);
+  mutex_bucket_lock(9);
+  CHECK_INT(pthread_create(&other, NULL, take_a_bucket, (void *)(intptr_t)10), 0);
+
+  CHECK_INT(waited_for_entry(2000), 1);
+  pthread_join(other, NULL);
+  mutex_bucket_unlock(9, 0);
+}
+
+void test_mutex(void) {
+  mutex_init();
+
+  case_a_hash_names_its_bucket();
+  case_every_bucket_is_its_own();
+  case_the_count_follows_what_unlock_is_told();
+  case_a_held_bucket_keeps_others_out();
+  case_another_bucket_is_free_meanwhile();
+
+  mutex_deinit();
+}