17 files changed, 639 insertions, 147 deletions

diff --git a/Makefile b/Makefile
index 61eb872..6a5a270 100644
--- a/Makefile
+++ b/Makefile
@@ -69,8 +69,8 @@ CFLAGS_libowfat=-I$(LIBOWFAT_HEADERS)
 LDFLAGS_libowfat=-L$(LIBOWFAT_LIBRARY) -lowfat
 
 BINARY =opentracker
-HEADERS=trackerlogic.h ot_urlencoded.h ot_batch.h ot_buf.h ot_event.h ot_fdstate.h ot_fmt.h ot_hex.h ot_ip.h ot_config.h ot_scan.h ot_socket.h ot_tcp.h ot_workqueue.h ot_mutex.h ot_random.h ot_stats.h ot_vector.h ot_clean.h ot_udp.h ot_iovec.h ot_fullscrape.h ot_accesslist.h ot_http.h ot_livesync.h ot_rijndael.h
-SOURCES=opentracker.c trackerlogic.c ot_urlencoded.c ot_batch.c ot_buf.c ot_event.c ot_fdstate.c ot_fmt.c ot_hex.c ot_ip.c ot_config.c ot_scan.c ot_socket.c ot_tcp.c ot_workqueue.c ot_mutex.c ot_random.c ot_stats.c ot_vector.c ot_clean.c ot_udp.c ot_iovec.c ot_fullscrape.c ot_accesslist.c ot_http.c ot_livesync.c ot_rijndael.c
+HEADERS=trackerlogic.h ot_urlencoded.h ot_batch.h ot_buf.h ot_event.h ot_fdstate.h ot_fmt.h ot_hex.h ot_ip.h ot_config.h ot_scan.h ot_socket.h ot_tcp.h ot_worker.h ot_workqueue.h ot_mutex.h ot_random.h ot_stats.h ot_vector.h ot_clean.h ot_udp.h ot_iovec.h ot_fullscrape.h ot_accesslist.h ot_http.h ot_livesync.h ot_rijndael.h
+SOURCES=opentracker.c trackerlogic.c ot_urlencoded.c ot_batch.c ot_buf.c ot_event.c ot_fdstate.c ot_fmt.c ot_hex.c ot_ip.c ot_config.c ot_scan.c ot_socket.c ot_tcp.c ot_worker.c ot_workqueue.c ot_mutex.c ot_random.c ot_stats.c ot_vector.c ot_clean.c ot_udp.c ot_iovec.c ot_fullscrape.c ot_accesslist.c ot_http.c ot_livesync.c ot_rijndael.c
 SOURCES_proxy=proxy.c ot_batch.c ot_fdstate.c ot_vector.c ot_mutex.c ot_random.c ot_scan.c ot_ip.c ot_socket.c
 
 all: $(BINARY) $(BINARY).debug
@@ -96,8 +96,8 @@ proxy.debug: $(SOURCES_proxy) $(HEADERS)
 # has to. tests/stubs.c supplies the few symbols those modules reference but
 # the tests never reach.
 TESTBIN=tests/runner
-TEST_SOURCES=tests/runner.c tests/test.c tests/stubs.c tests/t_urlencoded.c tests/t_iovec.c tests/t_vector.c tests/t_random.c tests/t_hex.c tests/t_accesslist.c tests/t_scan.c tests/t_buf.c tests/t_ip.c tests/t_socket.c tests/t_workqueue.c tests/t_batch.c tests/t_fdstate.c tests/t_event.c tests/t_fmt.c
-TEST_UNITS=ot_urlencoded.c ot_fmt.c ot_event.c ot_batch.c ot_fdstate.c ot_buf.c ot_ip.c ot_socket.c ot_iovec.c ot_vector.c ot_random.c ot_hex.c ot_scan.c ot_accesslist.c ot_mutex.c ot_workqueue.c
+TEST_SOURCES=tests/runner.c tests/test.c tests/stubs.c tests/t_urlencoded.c tests/t_iovec.c tests/t_vector.c tests/t_random.c tests/t_hex.c tests/t_accesslist.c tests/t_scan.c tests/t_buf.c tests/t_ip.c tests/t_socket.c tests/t_mutex.c tests/t_trackerlogic.c tests/t_workqueue.c tests/t_batch.c tests/t_fdstate.c tests/t_event.c tests/t_fmt.c
+TEST_UNITS=ot_urlencoded.c ot_fmt.c ot_event.c ot_batch.c ot_fdstate.c ot_buf.c ot_ip.c ot_socket.c ot_iovec.c ot_vector.c ot_random.c ot_hex.c ot_scan.c ot_accesslist.c ot_mutex.c ot_workqueue.c trackerlogic.c
 TEST_HEADERS=tests/test.h $(HEADERS)
 # Tests reach code that sits behind feature flags, so the units under test are
 # built with those features enabled. A test binary is not a production binary.
@@ -136,7 +136,7 @@ check-sanitize: $(TESTBIN).sanitize
 PYTHON?=python3
 # The client timeout is cut right down so that tests can reach the expiry
 # sweep. tests/integration/test_expiry.py mirrors these two numbers.
-FEATURES_integration=$(FEATURES) -DWANT_IP_FROM_QUERY_STRING -DWANT_ACCESSLIST_BLACK -DWANT_KEEPALIVE -DOT_CLIENT_TIMEOUT=5 -DOT_CLIENT_TIMEOUT_CHECKINTERVAL=1
+FEATURES_integration=$(FEATURES) -DWANT_IP_FROM_QUERY_STRING -DWANT_ACCESSLIST_BLACK -DWANT_DYNAMIC_ACCESSLIST -DWANT_KEEPALIVE -DOT_CLIENT_TIMEOUT=5 -DOT_CLIENT_TIMEOUT_CHECKINTERVAL=1
 CFLAGS_integration=$(CFLAGS) $(OPTS_debug) $(FEATURES_integration) -fsanitize=address,undefined -fno-omit-frame-pointer
 LDFLAGS_integration=$(LDFLAGS) -fsanitize=address,undefined
 
diff --git a/opentracker.c b/opentracker.c
index 2f2746d..644e99c 100644
--- a/opentracker.c
+++ b/opentracker.c
@@ -38,6 +38,7 @@
 #include "ot_stats.h"
 #include "ot_tcp.h"
 #include "ot_udp.h"
+#include "ot_worker.h"
 #include "trackerlogic.h"
 
 /* Globals */
@@ -429,8 +430,7 @@ int main(int argc, char **argv) {
   listen_start_udp_workers();
 
   server_mainloop(0);
-  tcp_workers_deinit();
-  udp_workers_deinit();
+  worker_stop_all();
 
   /* No thread is serving any more, so the teardown can run where a debugger
      and the sanitizers can follow it */
diff --git a/ot_accesslist.c b/ot_accesslist.c
index e8e0476..df084b8 100644
--- a/ot_accesslist.c
+++ b/ot_accesslist.c
@@ -273,7 +273,8 @@ static void *accesslist_worker(void *args) {
 }
 
 #ifdef WANT_DYNAMIC_ACCESSLIST
-static pthread_t thread_adder_id, thread_deleter_id;
+static pthread_t   thread_adder_id, thread_deleter_id;
+static _Atomic int adder_left, deleter_left;
 static void     *accesslist_adddel_worker(const char *fifoname, ot_accesslist *_Atomic *adding_to, ot_accesslist *_Atomic *removing_from) {
   struct stat st;
 
@@ -297,6 +298,9 @@ static void     *accesslist_adddel_worker(const char *fifoname, ot_accesslist *_
     ssize_t linelen;
 
     if (!fifo) {
+      /* Woken on purpose: the loop condition above decides what happens next */
+      if (errno == EINTR)
+        continue;
       fprintf(stderr, "Error when reading dynamic accesslists: Couldn't open FIFO at %s, error: %s\n", fifoname, strerror(errno));
       return NULL;
     }
@@ -324,8 +328,14 @@ static void     *accesslist_adddel_worker(const char *fifoname, ot_accesslist *_
           ptrdiff_t      off            = exactmatch - (*removing_from)->list;
           ot_accesslist *accesslist_new = accesslist_make(*removing_from, (*removing_from)->size - 1);
           if (accesslist_new) {
-            memcpy(accesslist_new->list, (*removing_from)->list, sizeof(ot_hash) * off);
-            memcpy(accesslist_new->list + off, (*removing_from)->list + off + 1, sizeof(ot_hash) * ((*removing_from)->size - off - 1));
+            size_t after = (*removing_from)->size - off - 1;
+
+            /* Removing the only entry leaves a list with no room at all, and
+               memcpy may not be handed that even for nothing */
+            if (off)
+              memcpy(accesslist_new->list, (*removing_from)->list, sizeof(ot_hash) * off);
+            if (after)
+              memcpy(accesslist_new->list + off, (*removing_from)->list + off + 1, sizeof(ot_hash) * after);
             (*removing_from)->base = time_now_minutes();
             *removing_from = accesslist_new;
           }
@@ -360,6 +370,7 @@ static void     *accesslist_adddel_worker(const char *fifoname, ot_accesslist *_
       pthread_mutex_unlock(&g_accesslist_mutex);
     }
 
+    free(line);
     fclose(fifo);
   }
   return NULL;
@@ -367,11 +378,30 @@ static void     *accesslist_adddel_worker(const char *fifoname, ot_accesslist *_
 
 static void *accesslist_adder_worker(void *args) {
   (void)args;
-  return accesslist_adddel_worker(g_accesslist_pipe_add, &g_accesslist_add, &g_accesslist_delete);
+  accesslist_adddel_worker(g_accesslist_pipe_add, &g_accesslist_add, &g_accesslist_delete);
+  atomic_store(&adder_left, 1);
+  return NULL;
 }
 static void *accesslist_deleter_worker(void *args) {
   (void)args;
-  return accesslist_adddel_worker(g_accesslist_pipe_delete, &g_accesslist_delete, &g_accesslist_add);
+  accesslist_adddel_worker(g_accesslist_pipe_delete, &g_accesslist_delete, &g_accesslist_add);
+  atomic_store(&deleter_left, 1);
+  return NULL;
+}
+
+/* These sit in a blocking open or read on a FIFO, so they are woken the way
+   the other workers are, and the signal is repeated because it only
+   interrupts a call already under way. The pipe name is what says whether
+   the thread was ever started. */
+static void accesslist_stop_fifo_worker(pthread_t thread, _Atomic int *left, const char *pipe_name) {
+  if (!pipe_name)
+    return;
+
+  while (!atomic_load(left)) {
+    pthread_kill(thread, OT_SIGNAL_WAKE);
+    usleep(1000);
+  }
+  pthread_join(thread, NULL);
 }
 #endif
 
@@ -392,6 +422,12 @@ void accesslist_deinit(void) {
   pthread_kill(thread_id, SIGHUP);
   pthread_join(thread_id, NULL);
 
+#ifdef WANT_DYNAMIC_ACCESSLIST
+  /* Before the lists they are reading are freed below */
+  accesslist_stop_fifo_worker(thread_adder_id, &adder_left, g_accesslist_pipe_add);
+  accesslist_stop_fifo_worker(thread_deleter_id, &deleter_left, g_accesslist_pipe_delete);
+#endif
+
   pthread_mutex_lock(&g_accesslist_mutex);
 
   g_accesslist = accesslist_free(g_accesslist);
diff --git a/ot_accesslist.h b/ot_accesslist.h
index 0a8bf4c..9c39a7a 100644
--- a/ot_accesslist.h
+++ b/ot_accesslist.h
@@ -14,6 +14,8 @@
 
 #if defined(WANT_ACCESSLIST_BLACK) || defined(WANT_ACCESSLIST_WHITE)
 #define WANT_ACCESSLIST
+/* Starts a thread that rereads the list when sent SIGHUP, and is stopped by
+   being sent one, so the caller blocks SIGHUP process wide beforehand */
 void         accesslist_init(void);
 void         accesslist_deinit(void);
 int          accesslist_hashisvalid(const ot_hash hash);
diff --git a/ot_mutex.c b/ot_mutex.c
index d856d5f..9b3fd24 100644
--- a/ot_mutex.c
+++ b/ot_mutex.c
@@ -30,8 +30,6 @@ static pthread_mutex_t bucket_mutex[OT_BUCKET_COUNT];
    threads out of that one bucket, so the counter needs its own protection */
 static _Atomic size_t  g_torrent_count;
 
-/* Self pipe from opentracker.c */
-
 ot_vector *mutex_bucket_lock(int bucket) {
   pthread_mutex_lock(bucket_mutex + bucket);
   return all_torrents + bucket;
@@ -66,7 +64,6 @@ void mutex_init(void) {
   memset(all_torrents, 0, sizeof(all_torrents));
 }
 
-/* Let every worker parked on the queue see that the tracker is stopping */
 void mutex_deinit(void) {
   size_t i;
   for (i = 0; i < OT_BUCKET_COUNT; ++i)
diff --git a/ot_tcp.c b/ot_tcp.c
index 47697ca..4a5008b 100644
--- a/ot_tcp.c
+++ b/ot_tcp.c
@@ -20,6 +20,7 @@
 #include "ot_http.h"
 #include "ot_mutex.h"
 #include "ot_socket.h"
+#include "ot_worker.h"
 #include "ot_stats.h"
 #include "ot_tcp.h"
 #include "trackerlogic.h"
@@ -164,75 +165,18 @@ void tcp_accept(const int64_t serversocket, struct ot_workstruct *ws) {
   }
 }
 
-/* One of these per worker, each allocated on its own so that growing the
-   array below never moves the one a running worker holds. */
-struct tcp_worker {
-  pthread_t   thread;
-  int64_t     sock;
-  _Atomic int left;
-};
-
-static struct tcp_worker **g_workers;
-static size_t              g_worker_count;
-
 /* A worker blocks in accept and nowhere else: the connection it is handed is
    non blocking, so a client that stops talking is given to the event loop
    rather than keeping this thread. */
-static void *tcp_worker(void *args) {
-  struct tcp_worker   *me = args;
-  struct ot_workstruct ws;
-
-  if (workstruct_init(&ws) == -1) {
-    fprintf(stderr, "Warning: a tcp worker could not get its buffers and will not run.\n");
-    atomic_store(&me->left, 1);
-    return NULL;
-  }
-
+static void tcp_run(struct ot_worker *me) {
   while (g_opentracker_running)
-    tcp_accept(me->sock, &ws);
-
-  workstruct_deinit(&ws);
-  atomic_store(&me->left, 1);
-  return NULL;
+    tcp_accept(me->sock, &me->ws);
 }
 
 void tcp_worker_install(int64_t sock) {
-  struct tcp_worker **grown = realloc(g_workers, (g_worker_count + 1) * sizeof(*g_workers));
-  struct tcp_worker  *worker;
-
-  if (!grown || !(worker = calloc(1, sizeof(*worker)))) {
-    fprintf(stderr, "Warning: out of memory installing a tcp worker, this socket stays with the workers already running.\n");
-    g_workers = grown ? grown : g_workers;
-    return;
-  }
-  g_workers    = grown;
-  worker->sock = sock;
-
   socket_set_blocking((int)sock, 1);
   socket_defer_accept((int)sock);
 
-  if (pthread_create(&worker->thread, NULL, tcp_worker, worker))
-    free(worker);
-  else
-    g_workers[g_worker_count++] = worker;
-}
-
-void tcp_workers_deinit(void) {
-  size_t i;
-
-  for (i = 0; i < g_worker_count; ++i) {
-    struct tcp_worker *worker = g_workers[i];
-
-    /* Repeated because a signal only interrupts a call already under way */
-    while (!atomic_load(&worker->left)) {
-      pthread_kill(worker->thread, OT_SIGNAL_WAKE);
-      usleep(1000);
-    }
-    pthread_join(worker->thread, NULL);
-    free(worker);
-  }
-
-  free(g_workers);
-  g_workers      = NULL;
-  g_worker_count = 0;
+  if (worker_start(tcp_run, sock) == -1)
+    fprintf(stderr, "Warning: could not install a tcp worker, this socket stays with the workers already running.\n");
 }
diff --git a/ot_tcp.h b/ot_tcp.h
index 96b6ec1..55a172c 100644
--- a/ot_tcp.h
+++ b/ot_tcp.h
@@ -22,7 +22,5 @@ void tcp_write(const int64_t sock);
 /* One thread accepting on one socket. Called once per worker. */
 void tcp_worker_install(int64_t sock);
 
-/* Stop every worker installed above and wait for it to be gone */
-void tcp_workers_deinit(void);
 
 #endif
diff --git a/ot_udp.c b/ot_udp.c
index 00ec566..309cbdb 100644
--- a/ot_udp.c
+++ b/ot_udp.c
@@ -16,21 +16,11 @@
 #include "ot_random.h"
 #include "ot_rijndael.h"
 #include "ot_socket.h"
+#include "ot_worker.h"
 #include "ot_stats.h"
 #include "ot_udp.h"
 #include "trackerlogic.h"
 
-/* One of these per worker, each allocated on its own so that growing the
-   array below never moves the one a running worker holds. */
-struct udp_worker {
-  pthread_t   thread;
-  int64_t     sock;
-  _Atomic int left;
-};
-
-static struct udp_worker **g_workers;
-static size_t              g_worker_count;
-
 static uint32_t g_rijndael_round_key[44] = {0};
 static volatile uint32_t g_key_of_the_hour[2] = {0};
 static volatile ot_time  g_hour_of_the_key;
@@ -217,22 +207,9 @@ int handle_udp6(int64_t serversocket, struct ot_workstruct *ws) {
   return 1;
 }
 
-static void *udp_worker(void *args) {
-  struct udp_worker   *me = args;
-  struct ot_workstruct ws;
-
-  if (workstruct_init(&ws) == -1) {
-    fprintf(stderr, "Warning: a udp worker could not get its buffers and will not run.\n");
-    atomic_store(&me->left, 1);
-    return NULL;
-  }
-
+static void udp_run(struct ot_worker *me) {
   while (g_opentracker_running)
-    handle_udp6(me->sock, &ws);
-
-  workstruct_deinit(&ws);
-  atomic_store(&me->left, 1);
-  return NULL;
+    handle_udp6(me->sock, &me->ws);
 }
 
 void udp_init(void) {
@@ -241,47 +218,11 @@ void udp_init(void) {
 }
 
 void udp_worker_install(int64_t sock) {
-  struct udp_worker **grown = realloc(g_workers, (g_worker_count + 1) * sizeof(*g_workers));
-  struct udp_worker  *worker;
-
-  if (!grown || !(worker = calloc(1, sizeof(*worker)))) {
-    fprintf(stderr, "Warning: out of memory installing a udp worker, this socket stays with the workers already running.\n");
-    g_workers = grown ? grown : g_workers;
-    return;
-  }
-  g_workers    = grown;
-  worker->sock = sock;
-
 #ifdef _DEBUG
   fprintf(stderr, "Installing a worker on udp socket %ld\n", (unsigned long)sock);
 #endif
   socket_set_blocking((int)sock, 1);
 
-  if (pthread_create(&worker->thread, NULL, udp_worker, worker))
-    free(worker);
-  else
-    g_workers[g_worker_count++] = worker;
+  if (worker_start(udp_run, sock) == -1)
+    fprintf(stderr, "Warning: could not install a udp worker, this socket stays with the workers already running.\n");
 }
-
-void udp_workers_deinit(void) {
-  size_t i;
-
-  for (i = 0; i < g_worker_count; ++i) {
-    struct udp_worker *worker = g_workers[i];
-
-    /* Repeated because a signal only interrupts a read already under way: a
-       worker that was between two reads when the first one arrived is inside
-       the next one by now. */
-    while (!atomic_load(&worker->left)) {
-      pthread_kill(worker->thread, OT_SIGNAL_WAKE);
-      usleep(1000);
-    }
-    pthread_join(worker->thread, NULL);
-    free(worker);
-  }
-
-  free(g_workers);
-  g_workers      = NULL;
-  g_worker_count = 0;
-}
-
diff --git a/ot_udp.h b/ot_udp.h
index b731aca..1cd363a 100644
--- a/ot_udp.h
+++ b/ot_udp.h
@@ -14,8 +14,6 @@ void udp_init(void);
 /* One thread reading one socket. Called once per worker. */
 void udp_worker_install(int64_t sock);
 
-/* Stop every worker installed above and wait for it to be gone */
-void udp_workers_deinit(void);
 int  handle_udp6(int64_t serversocket, struct ot_workstruct *ws);
 
 #endif
diff --git a/ot_worker.c b/ot_worker.c
new file mode 100644
index 0000000..97eaeb2
--- /dev/null
+++ b/ot_worker.c
@@ -0,0 +1,75 @@
+/* This software was written by Dirk Engling <erdgeist@erdgeist.org>
+   It is considered beerware. Prost. Skol. Cheers or whatever.
+
+   $id$ */
+
+/* System */
+#include <pthread.h>
+#include <stdatomic.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+/* Opentracker */
+#include "ot_worker.h"
+#include "trackerlogic.h"
+
+static struct ot_worker **g_workers;
+static size_t             g_worker_count;
+
+/* Everything a worker needs doing around its own loop, in one place, so that
+   a new kind of worker cannot miss a piece of it. */
+static void *worker_trampoline(void *args) {
+  struct ot_worker *me = args;
+
+  if (workstruct_init(&me->ws) == -1)
+    fprintf(stderr, "Warning: a worker could not get its buffers and will not run.\n");
+  else {
+    me->run(me);
+    workstruct_deinit(&me->ws);
+  }
+
+  atomic_store(&me->left, 1);
+  return NULL;
+}
+
+int worker_start(ot_worker_run run, int64_t sock) {
+  struct ot_worker **grown = realloc(g_workers, (g_worker_count + 1) * sizeof(*g_workers));
+  struct ot_worker  *worker;
+
+  if (!grown)
+    return -1;
+  g_workers = grown;
+
+  if (!(worker = calloc(1, sizeof(*worker))))
+    return -1;
+  worker->sock = sock;
+  worker->run  = run;
+
+  if (pthread_create(&worker->thread, NULL, worker_trampoline, worker)) {
+    free(worker);
+    return -1;
+  }
+  g_workers[g_worker_count++] = worker;
+  return 0;
+}
+
+void worker_stop_all(void) {
+  size_t i;
+
+  for (i = 0; i < g_worker_count; ++i) {
+    struct ot_worker *worker = g_workers[i];
+
+    /* Repeated because a signal only interrupts a call already under way */
+    while (!atomic_load(&worker->left)) {
+      pthread_kill(worker->thread, OT_SIGNAL_WAKE);
+      usleep(1000);
+    }
+    pthread_join(worker->thread, NULL);
+    free(worker);
+  }
+
+  free(g_workers);
+  g_workers      = NULL;
+  g_worker_count = 0;
+}
diff --git a/ot_worker.h b/ot_worker.h
new file mode 100644
index 0000000..ea4f379
--- /dev/null
+++ b/ot_worker.h
@@ -0,0 +1,39 @@
+/* This software was written by Dirk Engling <erdgeist@erdgeist.org>
+   It is considered beerware. Prost. Skol. Cheers or whatever.
+
+   $id$ */
+
+#ifndef OT_WORKER_H__
+#define OT_WORKER_H__
+
+#include <pthread.h>
+#include <stdatomic.h>
+#include <stdint.h>
+
+#include "trackerlogic.h"
+
+struct ot_worker;
+
+/* What a worker does between being started and being told to stop. It reads
+   worker->sock and works out of worker->ws; everything around it, from the
+   buffers to the counters to saying goodbye, is handled here. */
+typedef void (*ot_worker_run)(struct ot_worker *worker);
+
+/* A thread that serves requests on a socket of its own, with the buffers and
+   counters it needs. Each is allocated on its own, so taking on another one
+   never moves the record a running worker holds. */
+struct ot_worker {
+  pthread_t            thread;
+  _Atomic int          left;
+  int64_t              sock;
+  ot_worker_run        run;
+  struct ot_workstruct ws;
+};
+
+/* Start one. Returns -1 if it could not be started. */
+int  worker_start(ot_worker_run run, int64_t sock);
+
+/* Wake every worker until it has left, then join it */
+void worker_stop_all(void);
+
+#endif
diff --git a/tests/integration/test_dynamic_accesslist.py b/tests/integration/test_dynamic_accesslist.py
new file mode 100644
index 0000000..7fa5fde
--- /dev/null
+++ b/tests/integration/test_dynamic_accesslist.py
@@ -0,0 +1,50 @@
+"""Hashes added to and removed from the blacklist while the tracker runs.
+
+The two FIFOs are read by threads of their own, which is also what makes
+this the test that drives those threads through a shutdown.
+"""
+
+import os
+import time
+import unittest
+
+from harness import TrackerTestCase
+
+BLOCKED = bytes(range(1, 21))
+
+
+def as_hex(info_hash):
+    return "".join("%02x" % b for b in info_hash)
+
+
+class DynamicAccesslist(TrackerTestCase):
+    config = ("access.blacklist {dir}/blacklist\n"
+              "access.fifo_add {dir}/add.fifo\n"
+              "access.fifo_delete {dir}/delete.fifo\n")
+    files = {"blacklist": b""}
+
+    def feed(self, name, info_hash):
+        """Writing to the FIFO blocks until the reader has it, so this also
+           tells us the thread is alive."""
+        with open(os.path.join(self.tracker.dir, name), "w") as fifo:
+            fifo.write("%s added by a test\n" % as_hex(info_hash))
+
+    def wait_for(self, info_hash, blocked, patience=5.0):
+        """The reader thread picks the hash up on its own schedule, so this
+           waits for the answer to change rather than assuming it already has."""
+        deadline = time.time() + patience
+        while time.time() < deadline:
+            answer = self.tracker.announce(info_hash)
+            if (b"failure reason" in answer) == blocked:
+                return True
+            time.sleep(0.05)
+        return False
+
+    def test_a_hash_can_be_blocked_and_released_while_running(self):
+        self.assertNotIn(b"failure reason", self.tracker.announce(BLOCKED))
+
+        self.feed("add.fifo", BLOCKED)
+        self.assertTrue(self.wait_for(BLOCKED, blocked=True), "the hash was never blocked")
+
+        self.feed("delete.fifo", BLOCKED)
+        self.assertTrue(self.wait_for(BLOCKED, blocked=False), "the hash was never released")
diff --git a/tests/runner.c b/tests/runner.c
index 38bfb86..97c6d51 100644
--- a/tests/runner.c
+++ b/tests/runner.c
@@ -27,6 +27,8 @@ static const struct module modules[] = {{"ot_urlencoded", test_urlencoded},
                                         {"ot_buf", test_buf},
                                         {"ot_ip", test_ip},
                                         {"ot_socket", test_socket},
+                                        {"ot_mutex", test_mutex},
+                                        {"trackerlogic", test_trackerlogic},
                                         {"ot_workqueue", test_workqueue},
                                         {"ot_batch", test_batch},
                                         {"ot_fdstate", test_fdstate},
diff --git a/tests/stubs.c b/tests/stubs.c
index a8e6962..5999e2d 100644
--- a/tests/stubs.c
+++ b/tests/stubs.c
@@ -8,11 +8,9 @@
    behaviour should be supplied here rather than the test weakened. */
 
 /* Opentracker */
+#include "ot_stats.h"
 #include "trackerlogic.h"
 
-/* ot_vector.c calls this from vector_clean_list, which no test drives yet. */
-void free_peerlist(ot_peerlist *peer_list) { (void)peer_list; }
-
 /* ot_accesslist.c is built with WANT_ACCESSLIST_BLACK so that the hash parser
    is reachable. These two belong to accesslist_readfile and the reload worker,
    neither of which any test drives. */
@@ -26,3 +24,32 @@ long io_trywrite(long d, const char *buf, long len) {
   (void)buf;
   return len;
 }
+
+/* trackerlogic.c is under test, and starting it up starts every module it
+   leans on. None of them is driven by these tests, so they are answered here
+   rather than linked in and left to run threads of their own. */
+void clean_init(void) {}
+void clean_deinit(void) {}
+int  clean_single_torrent(ot_torrent *torrent) {
+  (void)torrent;
+  return 0;
+}
+void fullscrape_init(void) {}
+void fullscrape_deinit(void) {}
+void livesync_init(void) {}
+void livesync_deinit(void) {}
+void livesync_tell(struct ot_workstruct *ws) { (void)ws; }
+void stats_init(void) {}
+void stats_deinit(void) {}
+void stats_issue_event(struct ot_workstruct *ws, ot_status_event event, PROTO_FLAG proto, uintptr_t event_data) {
+  (void)ws;
+  (void)event;
+  (void)proto;
+  (void)event_data;
+}
+void stats_counters_register(struct ot_workstruct *ws) { (void)ws; }
+void stats_counters_retire(struct ot_workstruct *ws) { (void)ws; }
+
+const char *g_stats_path;
+ssize_t     g_stats_path_len;
+uint32_t    g_tracker_id;
diff --git a/tests/t_mutex.c b/tests/t_mutex.c
new file mode 100644
index 0000000..7c1463b
--- /dev/null
+++ b/tests/t_mutex.c
@@ -0,0 +1,138 @@
+/* This software was written by Dirk Engling <erdgeist@erdgeist.org>
+   It is considered beerware. Prost. Skol. Cheers or whatever.
+
+   $id$ */
+
+/* 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();
+}
diff --git a/tests/t_trackerlogic.c b/tests/t_trackerlogic.c
new file mode 100644
index 0000000..d3d8755
--- /dev/null
+++ b/tests/t_trackerlogic.c
@@ -0,0 +1,243 @@
+/* This software was written by Dirk Engling <erdgeist@erdgeist.org>
+   It is considered beerware. Prost. Skol. Cheers or whatever.
+
+   $id$ */
+
+/* System */
+#include <arpa/inet.h>
+#include <signal.h>
+#include <pthread.h>
+#include <string.h>
+
+/* Opentracker */
+#include "ot_mutex.h"
+#include "trackerlogic.h"
+#include "test.h"
+
+/* The swarm itself: what an announce does to a torrent, and what a scrape
+   says about it afterwards. The counts are read back through the udp scrape
+   because that is the one reply the tracker builds as plain numbers. */
+
+static struct ot_workstruct ws;
+
+static void                 hash_named(ot_hash hash, const char *name) {
+  memset(hash, 0, sizeof(ot_hash));
+  memcpy(hash, name, strlen(name) < sizeof(ot_hash) ? strlen(name) : sizeof(ot_hash));
+}
+
+/* An IPv4 peer arrives as the v4 mapped form the tracker stores */
+static void peer_v4(ot_peer6 peer, uint8_t last, uint16_t port) {
+  ot_ip6   ip = {0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0xff, 0xff, 10, 0, 0, 0};
+  uint16_t net_port = htons(port);
+
+  ip[15] = last;
+  memset(peer, 0, sizeof(ot_peer6));
+  OT_SETIP(peer, ip);
+  OT_SETPORT(peer, &net_port);
+  OT_PEERFLAG(peer) = 0;
+}
+
+static void peer_v6(ot_peer6 peer, uint8_t last, uint16_t port) {
+  ot_ip6   ip = {0x20, 0x01, 0x0d, 0xb8, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0};
+  uint16_t net_port = htons(port);
+
+  ip[15] = last;
+  memset(peer, 0, sizeof(ot_peer6));
+  OT_SETIP(peer, ip);
+  OT_SETPORT(peer, &net_port);
+  OT_PEERFLAG(peer) = 0;
+}
+
+static void announce(ot_hash *hash, ot_peer6 peer) {
+  ws.hash = hash;
+  memcpy(ws.peer, peer, sizeof(ot_peer6));
+  ws.reply = ws.outbuf;
+  add_peer_to_torrent_and_return_peers(FLAG_TCP, &ws, 50);
+}
+
+/* seeders, downloads completed, leechers */
+static void scrape(ot_hash hash, uint32_t counts[3]) {
+  char reply[12];
+
+  return_udp_scrape_for_torrent(hash, reply);
+  counts[0] = ntohl(((uint32_t *)reply)[0]);
+  counts[1] = ntohl(((uint32_t *)reply)[1]);
+  counts[2] = ntohl(((uint32_t *)reply)[2]);
+}
+
+static void case_an_announce_makes_a_torrent(void) {
+  ot_hash  hash;
+  ot_peer6 peer;
+  uint32_t counts[3];
+  size_t   before = mutex_get_torrent_count();
+
+  test_case("the first announce for a hash creates its torrent");
+  hash_named(hash, "first-announce");
+  peer_v4(peer, 1, 6881);
+  announce(&hash, peer);
+
+  CHECK_INT((int)(mutex_get_torrent_count() - before), 1);
+  scrape(hash, counts);
+  CHECK_INT((int)counts[2], 1); /* one leecher */
+  CHECK_INT((int)counts[0], 0);
+}
+
+static void case_the_same_peer_twice_is_one_peer(void) {
+  ot_hash  hash;
+  ot_peer6 peer;
+  uint32_t counts[3];
+
+  test_case("announcing twice renews a peer rather than adding another");
+  hash_named(hash, "renewing");
+  peer_v4(peer, 2, 6881);
+  announce(&hash, peer);
+  announce(&hash, peer);
+
+  scrape(hash, counts);
+  CHECK_INT((int)counts[2], 1);
+}
+
+static void case_a_port_makes_a_different_peer(void) {
+  ot_hash  hash;
+  ot_peer6 peer;
+  uint32_t counts[3];
+
+  test_case("the same address on another port is another peer");
+  hash_named(hash, "two-ports");
+  peer_v4(peer, 3, 6881);
+  announce(&hash, peer);
+  peer_v4(peer, 3, 6882);
+  announce(&hash, peer);
+
+  scrape(hash, counts);
+  CHECK_INT((int)counts[2], 2);
+}
+
+static void case_seeding_is_counted_apart(void) {
+  ot_hash  hash;
+  ot_peer6 peer;
+  uint32_t counts[3];
+
+  test_case("a seeder counts as complete, a leecher as incomplete");
+  hash_named(hash, "seed-and-leech");
+  peer_v4(peer, 4, 6881);
+  OT_PEERFLAG(peer) |= PEER_FLAG_SEEDING;
+  announce(&hash, peer);
+  peer_v4(peer, 5, 6881);
+  announce(&hash, peer);
+
+  scrape(hash, counts);
+  CHECK_INT((int)counts[0], 1);
+  CHECK_INT((int)counts[2], 1);
+}
+
+static void case_completion_without_seeding_is_not_believed(void) {
+  ot_hash  hash;
+  ot_peer6 peer;
+  uint32_t counts[3];
+
+  test_case("a peer that claims to have completed but is still leeching is not counted");
+  hash_named(hash, "claiming");
+  peer_v4(peer, 6, 6881);
+  OT_PEERFLAG(peer) |= PEER_FLAG_COMPLETED;
+  announce(&hash, peer);
+
+  scrape(hash, counts);
+  CHECK_INT((int)counts[1], 0);
+  CHECK_INT((int)counts[2], 1); /* still a leecher */
+}
+
+static void case_completing_is_counted_once(void) {
+  ot_hash  hash;
+  ot_peer6 peer;
+  uint32_t counts[3];
+
+  test_case("a seeder reporting completion is counted once, however often it says so");
+  hash_named(hash, "completing");
+  peer_v4(peer, 7, 6881);
+  OT_PEERFLAG(peer) |= PEER_FLAG_COMPLETED | PEER_FLAG_SEEDING;
+  announce(&hash, peer);
+  announce(&hash, peer);
+  announce(&hash, peer);
+
+  scrape(hash, counts);
+  CHECK_INT((int)counts[1], 1);
+  CHECK_INT((int)counts[0], 1);
+}
+
+static void case_a_peer_can_leave(void) {
+  ot_hash  hash;
+  ot_peer6 peer;
+  uint32_t counts[3];
+
+  test_case("a peer that stops is gone from the swarm");
+  hash_named(hash, "leaving");
+  peer_v4(peer, 7, 6881);
+  announce(&hash, peer);
+  peer_v4(peer, 8, 6881);
+  announce(&hash, peer);
+  scrape(hash, counts);
+  CHECK_INT((int)counts[2], 2);
+
+  ws.hash = &hash;
+  memcpy(ws.peer, peer, sizeof(ot_peer6));
+  remove_peer_from_torrent(FLAG_TCP, &ws);
+
+  scrape(hash, counts);
+  CHECK_INT((int)counts[2], 1);
+}
+
+static void case_the_families_are_kept_apart(void) {
+  ot_hash  hash;
+  ot_peer6 peer;
+  uint32_t counts[3];
+
+  test_case("a v4 and a v6 peer of one swarm are both counted");
+  hash_named(hash, "dual-stack");
+  peer_v4(peer, 9, 6881);
+  announce(&hash, peer);
+  peer_v6(peer, 9, 6881);
+  announce(&hash, peer);
+
+  scrape(hash, counts);
+  CHECK_INT((int)counts[2], 2);
+}
+
+static void case_a_hash_nobody_announced(void) {
+  ot_hash  hash;
+  uint32_t counts[3];
+
+  test_case("a hash nobody has announced scrapes as nothing at all");
+  hash_named(hash, "never-seen");
+  scrape(hash, counts);
+  CHECK_INT((int)counts[0], 0);
+  CHECK_INT((int)counts[1], 0);
+  CHECK_INT((int)counts[2], 0);
+}
+
+void test_trackerlogic(void) {
+  sigset_t signal_mask;
+
+  /* accesslist_init starts a thread that waits for SIGHUP and is stopped by
+     being sent one, so the signal has to be blocked here as the tracker
+     blocks it, or stopping the tracker logic ends this process instead */
+  sigemptyset(&signal_mask);
+  sigaddset(&signal_mask, SIGHUP);
+  pthread_sigmask(SIG_BLOCK, &signal_mask, NULL);
+
+  trackerlogic_init();
+  CHECK_INT(workstruct_init(&ws), 0);
+
+  case_an_announce_makes_a_torrent();
+  case_the_same_peer_twice_is_one_peer();
+  case_a_port_makes_a_different_peer();
+  case_seeding_is_counted_apart();
+  case_completion_without_seeding_is_not_believed();
+  case_completing_is_counted_once();
+  case_a_peer_can_leave();
+  case_the_families_are_kept_apart();
+  case_a_hash_nobody_announced();
+
+  workstruct_deinit(&ws);
+  trackerlogic_deinit();
+}
diff --git a/tests/test.h b/tests/test.h
index d58742c..d7296cc 100644
--- a/tests/test.h
+++ b/tests/test.h
@@ -86,6 +86,8 @@ void test_scan(void);
 void test_buf(void);
 void test_ip(void);
 void test_socket(void);
+void test_mutex(void);
+void test_trackerlogic(void);
 void test_workqueue(void);
 void test_batch(void);
 void test_fdstate(void);