+#define SENTINEL 0 // This forbids putting a mutex/condition variable at the front.
+#define OFFSET_ARRAY(...) __VA_ARGS__, SENTINEL
+#define DEFINE_OFFSET_ARRAY(type, name, mutexes, conds) \
+static const unsigned name ## _offsets[] = { offsetof(type, pthread_init_cnt),\
+ OFFSET_ARRAY mutexes, \
+ OFFSET_ARRAY conds }
+
+#define OFF(member) offsetof(FrameThreadContext, member)
+DEFINE_OFFSET_ARRAY(FrameThreadContext, thread_ctx,
+ (OFF(buffer_mutex), OFF(hwaccel_mutex), OFF(async_mutex)),
+ (OFF(async_cond)));
+#undef OFF
+
+#define OFF(member) offsetof(PerThreadContext, member)
+DEFINE_OFFSET_ARRAY(PerThreadContext, per_thread,
+ (OFF(progress_mutex), OFF(mutex)),
+ (OFF(input_cond), OFF(progress_cond), OFF(output_cond)));
+#undef OFF
+
+static av_cold void free_pthread(void *obj, const unsigned offsets[])
+{
+ unsigned cnt = *(unsigned*)((char*)obj + offsets[0]);
+ const unsigned *cur_offset = offsets;
+
+ for (; *(++cur_offset) != SENTINEL && cnt; cnt--)
+ pthread_mutex_destroy((pthread_mutex_t*)((char*)obj + *cur_offset));
+ for (; *(++cur_offset) != SENTINEL && cnt; cnt--)
+ pthread_cond_destroy ((pthread_cond_t *)((char*)obj + *cur_offset));
+}
+
+static av_cold int init_pthread(void *obj, const unsigned offsets[])
+{
+ const unsigned *cur_offset = offsets;
+ unsigned cnt = 0;
+ int err;
+
+#define PTHREAD_INIT_LOOP(type) \
+ for (; *(++cur_offset) != SENTINEL; cnt++) { \
+ pthread_ ## type ## _t *dst = (void*)((char*)obj + *cur_offset); \
+ err = pthread_ ## type ## _init(dst, NULL); \
+ if (err) { \
+ err = AVERROR(err); \
+ goto fail; \
+ } \
+ }
+ PTHREAD_INIT_LOOP(mutex)
+ PTHREAD_INIT_LOOP(cond)
+
+fail:
+ *(unsigned*)((char*)obj + offsets[0]) = cnt;
+ return err;
+}
+