Mesa (main): mesa: use atomics instead of mutexes for refcounting texture objects

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Module: Mesa
Branch: main
Commit: 0b1914a7c194113df931bdf363e04e8e376155dd
URL:    http://cgit.freedesktop.org/mesa/mesa/commit/?id=0b1914a7c194113df931bdf363e04e8e376155dd

Author: Marek Olšák <marek.olsak at amd.com>
Date:   Mon Jun  7 09:26:55 2021 -0400

mesa: use atomics instead of mutexes for refcounting texture objects

Reviewed-By: Mike Blumenkrantz <michael.blumenkrantz at gmail.com>
Reviewed-by: Emma Anholt <emma at anholt.net>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/11339>

---

 src/mesa/main/mtypes.h |  1 -
 src/mesa/main/texobj.c | 23 ++++-------------------
 2 files changed, 4 insertions(+), 20 deletions(-)

diff --git a/src/mesa/main/mtypes.h b/src/mesa/main/mtypes.h
index e7474ad0262..936b1511162 100644
--- a/src/mesa/main/mtypes.h
+++ b/src/mesa/main/mtypes.h
@@ -966,7 +966,6 @@ struct gl_sampler_object
  */
 struct gl_texture_object
 {
-   simple_mtx_t Mutex;         /**< for thread safety */
    GLint RefCount;             /**< reference count */
    GLuint Name;                /**< the user-visible texture object ID */
    GLenum16 Target;            /**< GL_TEXTURE_1D, GL_TEXTURE_2D, etc. */
diff --git a/src/mesa/main/texobj.c b/src/mesa/main/texobj.c
index 4b8a1260593..b5b873b3ebd 100644
--- a/src/mesa/main/texobj.c
+++ b/src/mesa/main/texobj.c
@@ -313,7 +313,6 @@ _mesa_initialize_texture_object( struct gl_context *ctx,
 
    memset(obj, 0, sizeof(*obj));
    /* init the non-zero fields */
-   simple_mtx_init(&obj->Mutex, mtx_plain);
    obj->RefCount = 1;
    obj->Name = name;
    obj->Target = target;
@@ -449,10 +448,6 @@ _mesa_delete_texture_object(struct gl_context *ctx,
    _mesa_delete_texture_handles(ctx, texObj);
 
    _mesa_reference_buffer_object_shared(ctx, &texObj->BufferObject, NULL);
-
-   /* destroy the mutex -- it may have allocated memory (eg on bsd) */
-   simple_mtx_destroy(&texObj->Mutex);
-
    free(texObj->Label);
 
    /* free this object */
@@ -538,20 +533,14 @@ _mesa_reference_texobj_(struct gl_texture_object **ptr,
 
    if (*ptr) {
       /* Unreference the old texture */
-      GLboolean deleteFlag = GL_FALSE;
       struct gl_texture_object *oldTex = *ptr;
 
       assert(valid_texture_object(oldTex));
       (void) valid_texture_object; /* silence warning in release builds */
 
-      simple_mtx_lock(&oldTex->Mutex);
       assert(oldTex->RefCount > 0);
-      oldTex->RefCount--;
-
-      deleteFlag = (oldTex->RefCount == 0);
-      simple_mtx_unlock(&oldTex->Mutex);
 
-      if (deleteFlag) {
+      if (p_atomic_dec_zero(&oldTex->RefCount)) {
          /* Passing in the context drastically changes the driver code for
           * framebuffer deletion.
           */
@@ -561,21 +550,17 @@ _mesa_reference_texobj_(struct gl_texture_object **ptr,
          else
             _mesa_problem(NULL, "Unable to delete texture, no context");
       }
-
-      *ptr = NULL;
    }
-   assert(!*ptr);
 
    if (tex) {
       /* reference new texture */
       assert(valid_texture_object(tex));
-      simple_mtx_lock(&tex->Mutex);
       assert(tex->RefCount > 0);
 
-      tex->RefCount++;
-      *ptr = tex;
-      simple_mtx_unlock(&tex->Mutex);
+      p_atomic_inc(&tex->RefCount);
    }
+
+   *ptr = tex;
 }