From c5582317b35f2d333c750246bbf10b58ff2f7fa9 Mon Sep 17 00:00:00 2001
From: Mike Klein <mtklein@google.com>
Date: Mon, 1 Mar 2021 11:24:27 -0600
Subject: [PATCH] make SkExecutor::GetDefault() a little threadsafe

We note SetDefault() isn't threadsafe, but don't mention anything about
GetDefault().  So it feels like it ought to be thread safe.

But it's not threadsafe as-is, since it writes to gDefaultExecutor.
With tiny tweaks we can make it instead only read gDefaultExecutor.

Change-Id: If229afda3d0bfb4fe491137fd2fc2226d0eafafa
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/377918
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
---
 src/core/SkExecutor.cpp | 22 ++++++++++------------
 1 file changed, 10 insertions(+), 12 deletions(-)

diff --git a/src/core/SkExecutor.cpp b/src/core/SkExecutor.cpp
index 6ed366f55e..8b12b467ab 100644
--- a/src/core/SkExecutor.cpp
+++ b/src/core/SkExecutor.cpp
@@ -36,24 +36,22 @@ class SkTrivialExecutor final : public SkExecutor {
     }
 };
 
+static SkExecutor& trivial_executor() {
+    static auto* executor = new SkTrivialExecutor();
+    return *executor;
+}
+
 static SkExecutor* gDefaultExecutor = nullptr;
 
-void SetDefaultTrivialExecutor() {
-    static SkTrivialExecutor *gTrivial = new SkTrivialExecutor();
-    gDefaultExecutor = gTrivial;
-}
 SkExecutor& SkExecutor::GetDefault() {
-    if (!gDefaultExecutor) {
-        SetDefaultTrivialExecutor();
+    if (gDefaultExecutor) {
+        return *gDefaultExecutor;
     }
-    return *gDefaultExecutor;
+    return trivial_executor();
 }
+
 void SkExecutor::SetDefault(SkExecutor* executor) {
-    if (executor) {
-        gDefaultExecutor = executor;
-    } else {
-        SetDefaultTrivialExecutor();
-    }
+    gDefaultExecutor = executor;
 }
 
 // We'll always push_back() new work, but pop from the front of deques or the back of SkTArray.