From 00b46455a065d33cb01dc6345637b38c3309596d Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Daniel=20Ekl=C3=B6f?= <daniel@ekloef.se>
Date: Sat, 2 Nov 2019 00:33:37 +0100
Subject: [PATCH] shm: associate a 'cookie' with each buffer

When re-using a buffer from cache, only re-use ones with a matching
cookie.

This prevents contention between multiple terminal windows.
---
 render.c | 12 ++++++++----
 shm.c    | 14 ++++++++++----
 shm.h    |  5 ++++-
 3 files changed, 22 insertions(+), 9 deletions(-)

diff --git a/render.c b/render.c
index 37d1aee1..0b0c6d5b 100644
--- a/render.c
+++ b/render.c
@@ -441,10 +441,13 @@ grid_render(struct terminal *term)
     assert(term->width > 0);
     assert(term->height > 0);
 
-    struct buffer *buf = shm_get_buffer(term->wl->shm, term->width, term->height);
-    wl_surface_attach(term->window->surface, buf->wl_buf, 0, 0);
-    pixman_image_t *pix = buf->pix;
+    unsigned long cookie = (uintptr_t)term;
+    struct buffer *buf = shm_get_buffer(
+        term->wl->shm, term->width, term->height, cookie);
 
+    wl_surface_attach(term->window->surface, buf->wl_buf, 0, 0);
+
+    pixman_image_t *pix = buf->pix;
     bool all_clean = tll_length(term->grid->scroll_damage) == 0;
 
     /* If we resized the window, or is flashing, or just stopped flashing */
@@ -754,7 +757,8 @@ render_search_box(struct terminal *term)
     const int width = 2 * margin + max(20, term->search.len) * term->cell_width;
     const int height = 2 * margin + 1 * term->cell_height;
 
-    struct buffer *buf = shm_get_buffer(term->wl->shm, width, height);
+    unsigned long cookie = (uintptr_t)term;
+    struct buffer *buf = shm_get_buffer(term->wl->shm, width, height, cookie);
 
     /* Background - yellow on empty/match, red on mismatch */
     pixman_color_t color = color_hex_to_pixman(
diff --git a/shm.c b/shm.c
index fd962698..7c649ac3 100644
--- a/shm.c
+++ b/shm.c
@@ -10,7 +10,7 @@
 #include <pixman.h>
 
 #define LOG_MODULE "shm"
-#define LOG_ENABLE_DBG 1
+#define LOG_ENABLE_DBG 0
 #include "log.h"
 #include "stride.h"
 #include "tllist.h"
@@ -31,13 +31,18 @@ static const struct wl_buffer_listener buffer_listener = {
 };
 
 struct buffer *
-shm_get_buffer(struct wl_shm *shm, int width, int height)
+shm_get_buffer(struct wl_shm *shm, int width, int height, unsigned long cookie)
 {
     tll_foreach(buffers, it) {
-        if (it->item.width != width || it->item.height != height)
+        if (it->item.width != width)
+            continue;
+        if (it->item.height != height)
+            continue;
+        if (it->item.cookie != cookie)
             continue;
 
         if (!it->item.busy) {
+            LOG_DBG("cookie=%lx: re-using buffer from cache", cookie);
             it->item.busy = true;
             return &it->item;
         }
@@ -73,7 +78,7 @@ shm_get_buffer(struct wl_shm *shm, int width, int height)
 
     /* Total size */
     size = stride * height;
-    LOG_DBG("allocating a %zu KB pool", size / 1024);
+    LOG_DBG("cookie=%lx: allocating new buffer: %zu KB", cookie, size / 1024);
 
     if (ftruncate(pool_fd, size) == -1) {
         LOG_ERRNO("failed to truncate SHM pool");
@@ -111,6 +116,7 @@ shm_get_buffer(struct wl_shm *shm, int width, int height)
     tll_push_back(
         buffers,
         ((struct buffer){
+            .cookie = cookie,
             .width = width,
             .height = height,
             .stride = stride,
diff --git a/shm.h b/shm.h
index 312d45a9..555c5d51 100644
--- a/shm.h
+++ b/shm.h
@@ -7,6 +7,8 @@
 #include <wayland-client.h>
 
 struct buffer {
+    unsigned long cookie;
+
     int width;
     int height;
     int stride;
@@ -19,5 +21,6 @@ struct buffer {
     pixman_image_t *pix;
 };
 
-struct buffer *shm_get_buffer(struct wl_shm *shm, int width, int height);
+struct buffer *shm_get_buffer(
+    struct wl_shm *shm, int width, int height, unsigned long cookie);
 void shm_fini(void);