htsthread_wait() returned before threads it should join had started

process_chain was incremented by the child in hts_entry_point(), so a caller
that spawned threads and immediately called htsthread_wait() saw a zero count
and returned at once, free to tear down state the children were about to read.

Count at spawn instead, under the same mutex the waiter reads.

httrack.c freed the option block before waiting; wait first.

Closes #747

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>
Signed-off-by: Xavier Roche <xroche@gmail.com>

src/htsthread.c

@@ -44,9 +44,18 @@ Please visit our Website: http://www.httrack.com
 #endif
 #endif
 
+/* Outstanding threads, counted at spawn rather than by the child at entry, so
+   that a caller which spawns and immediately waits still joins them (#747). */
 static int process_chain = 0;
 static htsmutex process_chain_mutex = HTSMUTEX_INIT;
 
+static void process_chain_add(int delta) {
+  hts_mutexlock(&process_chain_mutex);
+  process_chain += delta;
+  assertf(process_chain >= 0);
+  hts_mutexrelease(&process_chain_mutex);
+}
+
 HTSEXT_API void htsthread_wait(void) {
   htsthread_wait_n(0);
 }
@@ -99,20 +108,12 @@ static void *hts_entry_point(void *tharg)
   void *const arg = s_args->arg;
   void (*fun) (void *arg) = s_args->fun;
 
-  free(tharg);
-
-  hts_mutexlock(&process_chain_mutex);
-  process_chain++;
-  assertf(process_chain > 0);
-  hts_mutexrelease(&process_chain_mutex);
+  freet(tharg);
 
   /* run */
   fun(arg);
 
-  hts_mutexlock(&process_chain_mutex);
-  process_chain--;
-  assertf(process_chain >= 0);
-  hts_mutexrelease(&process_chain_mutex);
+  process_chain_add(-1);
 #ifdef _WIN32
   return 0;
 #else
@@ -122,18 +123,20 @@ static void *hts_entry_point(void *tharg)
 
 /* create a thread */
 HTSEXT_API int hts_newthread(void (*fun) (void *arg), void *arg) {
-  hts_thread_s *s_args = malloc(sizeof(hts_thread_s));
+  hts_thread_s *s_args = malloct(sizeof(hts_thread_s));
 
   assertf(s_args != NULL);
   s_args->arg = arg;
   s_args->fun = fun;
+  process_chain_add(1);
 #ifdef _WIN32
   {
     unsigned int idt;
     HANDLE handle =
       (HANDLE) _beginthreadex(NULL, 0, hts_entry_point, s_args, 0, &idt);
     if (handle == 0) {
-      free(s_args);
+      process_chain_add(-1);
+      freet(s_args);
       return -1;
     } else {
       /* detach the thread from the main process so that is can be independent */
@@ -151,7 +154,8 @@ HTSEXT_API int hts_newthread(void (*fun) (void *arg), void *arg) {
         || pthread_attr_setstacksize(&attr, stackSize) != 0
         || (retcode =
             pthread_create(&handle, &attr, hts_entry_point, s_args)) != 0) {
-      free(s_args);
+      process_chain_add(-1);
+      freet(s_args);
       return -1;
     } else {
       /* detach the thread from the main process so that is can be independent */

src/httrack.c

@@ -306,8 +306,8 @@ int main(int argc, char **argv) {
     fprintf(stderr, "* %s\n", hts_errmsg(opt));
   }
   global_opt = NULL;
+  htsthread_wait(); /* pending threads still read opt */
   hts_free_opt(opt);
-  htsthread_wait();             /* wait for pending threads */
   hts_uninit();
 
 #ifdef _WIN32