From 57cd0a0a28c1bf5d489c58afad309011836fce93 Mon Sep 17 00:00:00 2001
From: Hans-Kristian Arntzen <post@arntzen-software.no>
Date: Thu, 18 Jan 2024 17:05:39 +0100
Subject: [PATCH] wsi/x11: Make chain->status atomic.

Avoids having to take extra locks in acquire/present.

Signed-off-by: Hans-Kristian Arntzen <post@arntzen-software.no>
Reviewed-By: Mike Blumenkrantz <michael.blumenkrantz@gmail.com>
Acked-by: Adam Jackson <ajax@redhat.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/26954>
---
 src/vulkan/wsi/wsi_common_x11.c | 20 ++++++++++++--------
 1 file changed, 12 insertions(+), 8 deletions(-)

diff --git a/src/vulkan/wsi/wsi_common_x11.c b/src/vulkan/wsi/wsi_common_x11.c
index e2b14f2d720..417d7cc10b9 100644
--- a/src/vulkan/wsi/wsi_common_x11.c
+++ b/src/vulkan/wsi/wsi_common_x11.c
@@ -35,6 +35,7 @@
 #include <xcb/shm.h>
 
 #include "util/macros.h"
+#include <stdatomic.h>
 #include <stdlib.h>
 #include <stdio.h>
 #include <unistd.h>
@@ -1086,7 +1087,7 @@ struct x11_swapchain {
    uint32_t                                     stamp;
    uint32_t                                     sent_image_count;
 
-   VkResult                                     status;
+   atomic_int                                   status;
    bool                                         copy_is_suboptimal;
    struct wsi_queue                             present_queue;
    struct wsi_queue                             acquire_queue;
@@ -1501,12 +1502,11 @@ x11_capture_trace(struct x11_swapchain *chain)
 #endif
 }
 
+/* Use a trivial helper here to make it easier to read in code
+ * where we're intending to access chain->status outside the thread lock. */
 static VkResult x11_swapchain_read_status_atomic(struct x11_swapchain *chain)
 {
-   pthread_mutex_lock(&chain->thread_state_lock);
-   VkResult status = chain->status;
-   pthread_mutex_unlock(&chain->thread_state_lock);
-   return status;
+   return chain->status;
 }
 
 /**
@@ -1612,9 +1612,13 @@ x11_acquire_next_image(struct wsi_swapchain *anv_chain,
    if (result == VK_TIMEOUT)
       return info->timeout ? VK_TIMEOUT : VK_NOT_READY;
 
-   pthread_mutex_lock(&chain->thread_state_lock);
-   result = x11_swapchain_result(chain, result);
-   pthread_mutex_unlock(&chain->thread_state_lock);
+   if (result < 0) {
+      pthread_mutex_lock(&chain->thread_state_lock);
+      result = x11_swapchain_result(chain, result);
+      pthread_mutex_unlock(&chain->thread_state_lock);
+   } else {
+      result = x11_swapchain_read_status_atomic(chain);
+   }
 
    if (result < 0)
       return result;