avcodec/pthread_frame: Check initializing mutexes/condition variables

Up until now, initializing the mutexes/condition variables wasn't
checked by ff_frame_thread_init(). This commit changes this.

Given that it is not documented to be save to destroy a zeroed but
otherwise uninitialized mutex/condition variable, one has to choose
between two approaches: Either one duplicates the code to free them
in ff_frame_thread_init() in case of errors or one records which have
been successfully initialized. This commit takes the latter approach:
For each of the two structures with mutexes/condition variables
an array containing the offsets of the members to initialize is added.
Said array is used both for initializing and freeing and the only thing
that needs to be recorded is how many of these have been successfully
initialized.

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

libavcodec/pthread_frame.c

@@ -78,6 +78,7 @@ typedef struct PerThreadContext {
 
     pthread_t      thread;
     int            thread_init;
+    unsigned       pthread_init_cnt;///< Number of successfully initialized mutexes/conditions
     pthread_cond_t input_cond;      ///< Used to wait for a new packet from the main thread.
     pthread_cond_t progress_cond;   ///< Used by child threads to wait for progress to change.
     pthread_cond_t output_cond;     ///< Used by the main thread to wait for frames to finish.
@@ -126,6 +127,7 @@ typedef struct FrameThreadContext {
     PerThreadContext *threads;     ///< The contexts for each thread.
     PerThreadContext *prev_thread; ///< The last thread submit_packet() was called on.
 
+    unsigned    pthread_init_cnt;  ///< Number of successfully initialized mutexes/conditions
     pthread_mutex_t buffer_mutex;  ///< Mutex used to protect get/release_buffer().
     /**
      * This lock is used for ensuring threads run in serial when hwaccel
@@ -680,6 +682,59 @@ static void park_frame_worker_threads(FrameThreadContext *fctx, int thread_count
     async_lock(fctx);
 }
 
+#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;
+}
+
 void ff_frame_thread_free(AVCodecContext *avctx, int thread_count)
 {
     FrameThreadContext *fctx = avctx->internal->thread_ctx;
@@ -739,21 +794,14 @@ void ff_frame_thread_free(AVCodecContext *avctx, int thread_count)
 
         av_frame_free(&p->frame);
 
-        pthread_mutex_destroy(&p->mutex);
-        pthread_mutex_destroy(&p->progress_mutex);
-        pthread_cond_destroy(&p->input_cond);
-        pthread_cond_destroy(&p->progress_cond);
-        pthread_cond_destroy(&p->output_cond);
+        free_pthread(p, per_thread_offsets);
         av_packet_free(&p->avpkt);
 
         av_freep(&p->avctx);
     }
 
     av_freep(&fctx->threads);
-    pthread_mutex_destroy(&fctx->buffer_mutex);
-    pthread_mutex_destroy(&fctx->hwaccel_mutex);
-    pthread_mutex_destroy(&fctx->async_mutex);
-    pthread_cond_destroy(&fctx->async_cond);
+    free_pthread(fctx, thread_ctx_offsets);
 
     av_freep(&avctx->internal->thread_ctx);
 
@@ -780,12 +828,6 @@ static av_cold int init_thread(PerThreadContext *p, int *threads_to_free,
      * ff_frame_thread_free in case of errors. */
     (*threads_to_free)++;
 
-        pthread_mutex_init(&p->mutex, NULL);
-        pthread_mutex_init(&p->progress_mutex, NULL);
-        pthread_cond_init(&p->input_cond, NULL);
-        pthread_cond_init(&p->progress_cond, NULL);
-        pthread_cond_init(&p->output_cond, NULL);
-
     p->parent = fctx;
     p->avctx  = copy;
 
@@ -810,6 +852,10 @@ static av_cold int init_thread(PerThreadContext *p, int *threads_to_free,
             }
         }
 
+    err = init_pthread(p, per_thread_offsets);
+    if (err < 0)
+        return err;
+
     if (!(p->frame = av_frame_alloc()) ||
         !(p->avpkt = av_packet_alloc()))
         return AVERROR(ENOMEM);
@@ -846,7 +892,7 @@ int ff_frame_thread_init(AVCodecContext *avctx)
     const AVCodec *codec = avctx->codec;
     AVCodecContext *src = avctx;
     FrameThreadContext *fctx;
-    int i, err = 0;
+    int err, i = 0;
 
     if (!thread_count) {
         int nb_cpus = av_cpu_count();
@@ -866,24 +912,26 @@ int ff_frame_thread_init(AVCodecContext *avctx)
     if (!fctx)
         return AVERROR(ENOMEM);
 
-    fctx->threads = av_mallocz_array(thread_count, sizeof(PerThreadContext));
-    if (!fctx->threads) {
+    err = init_pthread(fctx, thread_ctx_offsets);
+    if (err < 0) {
+        free_pthread(fctx, thread_ctx_offsets);
         av_freep(&avctx->internal->thread_ctx);
-        return AVERROR(ENOMEM);
+        return err;
     }
 
-    pthread_mutex_init(&fctx->buffer_mutex, NULL);
-    pthread_mutex_init(&fctx->hwaccel_mutex, NULL);
-    pthread_mutex_init(&fctx->async_mutex, NULL);
-    pthread_cond_init(&fctx->async_cond, NULL);
-
     fctx->async_lock = 1;
     fctx->delaying = 1;
 
     if (codec->type == AVMEDIA_TYPE_VIDEO)
         avctx->delay = src->thread_count - 1;
 
-    for (i = 0; i < thread_count; ) {
+    fctx->threads = av_mallocz_array(thread_count, sizeof(PerThreadContext));
+    if (!fctx->threads) {
+        err = AVERROR(ENOMEM);
+        goto error;
+    }
+
+    for (; i < thread_count; ) {
         PerThreadContext *p  = &fctx->threads[i];
         int first = !i;