vulkan: fix use of atomics for the current context index

The code used to use atomic, but over time, this got broken.
This commit also remmoves the is-the-last-submission-ready
shortcut, which rarely did anything.
There's also value in relying on the fact that contexts
always carry their frames in a strictly incremental order
with no gaps.

libavutil/vulkan.c

@@ -317,6 +317,8 @@ int ff_vk_exec_pool_init(FFVulkanContext *s, FFVkQueueFamilyCtx *qf,
 
     const VkQueryPoolVideoEncodeFeedbackCreateInfoKHR *ef = NULL;
 
+    atomic_init(&pool->idx, 0);
+
     if (query_type == VK_QUERY_TYPE_VIDEO_ENCODE_FEEDBACK_KHR) {
         ef = ff_vk_find_struct(query_create_pnext,
                                VK_STRUCTURE_TYPE_QUERY_POOL_VIDEO_ENCODE_FEEDBACK_CREATE_INFO_KHR);
@@ -490,17 +492,7 @@ VkResult ff_vk_exec_get_query(FFVulkanContext *s, FFVkExecContext *e,
 
 FFVkExecContext *ff_vk_exec_get(FFVulkanContext *s, FFVkExecPool *pool)
 {
-    FFVulkanFunctions *vk = &s->vkfn;
-    FFVkExecContext *e = &pool->contexts[pool->idx];
-
-    /* Check if last submission has already finished.
-     * If so, don't waste resources and reuse the same buffer. */
-    if (e->had_submission &&
-        vk->GetFenceStatus(s->hwctx->act_dev, e->fence) == VK_SUCCESS)
-        return e;
-
-    pool->idx = (pool->idx + 1) % pool->pool_size;
-    return &pool->contexts[pool->idx];
+    return &pool->contexts[atomic_fetch_add(&pool->idx, 1) % pool->pool_size];
 }
 
 void ff_vk_exec_wait(FFVulkanContext *s, FFVkExecContext *e)

libavutil/vulkan.h

@@ -248,7 +248,7 @@ typedef struct FFVulkanShaderData {
 
 typedef struct FFVkExecPool {
     FFVkExecContext *contexts;
-    atomic_int_least64_t idx;
+    atomic_uint_least64_t idx;
 
     VkCommandPool cmd_buf_pool;
     VkCommandBuffer *cmd_bufs;