commit 8d7d0f42c697ad893df9249b6e66684adb9439f5
author Alec Mouri <alecmouri@google.com> Tue May 10 23:33:40 2022 +0000
committer Alec Mouri <alecmouri@google.com> Mon May 16 22:31:01 2022 +0000
tree 84aa7730c4c3ea2d6d88ffb4f2129273638cc636
parent 04d24da36e27766f09fc871307b58cb4303b0082

Use semaphore instead of condition variable

BackgroundExecutor uses a condition variable to synchronize processing
to a work queue, which means that there is possible mutex contention on
the main thread in rare scenarios.

Instead, we can make the main thread non-blocking with a thread-safe
queue, and use semaphores for signaling the background thread to wake
up. Using semaphores saves a small number of instructions, but overall
reduces contention

Bug: 232113929
Test: bouncy ball

Change-Id: Iced25e8349bdb2a70cac1ed681059a0b14258407

services/surfaceflinger/SurfaceFlinger.cpp

diff --git a/services/surfaceflinger/SurfaceFlinger.cpp b/services/surfaceflinger/SurfaceFlinger.cpp
index d93281b..1495249 100644
--- a/services/surfaceflinger/SurfaceFlinger.cpp
+++ b/services/surfaceflinger/SurfaceFlinger.cpp
@@ -3226,12 +3226,12 @@
     if (!updateWindowInfo && mInputWindowCommands.empty()) {
         return;
     }
-    BackgroundExecutor::getInstance().execute([updateWindowInfo,
-                                               windowInfos = std::move(windowInfos),
-                                               displayInfos = std::move(displayInfos),
-                                               inputWindowCommands =
-                                                       std::move(mInputWindowCommands),
-                                               inputFlinger = mInputFlinger, this]() {
+    BackgroundExecutor::getInstance().sendCallbacks({[updateWindowInfo,
+                                                      windowInfos = std::move(windowInfos),
+                                                      displayInfos = std::move(displayInfos),
+                                                      inputWindowCommands =
+                                                              std::move(mInputWindowCommands),
+                                                      inputFlinger = mInputFlinger, this]() {
         ATRACE_NAME("BackgroundExecutor::updateInputFlinger");
         if (updateWindowInfo) {
             mWindowInfosListenerInvoker->windowInfosChanged(windowInfos, displayInfos,
@@ -3244,7 +3244,7 @@
         for (const auto& focusRequest : inputWindowCommands.focusRequests) {
             inputFlinger->setFocusedWindow(focusRequest);
         }
-    });
+    }});
 
     mInputWindowCommands.clear();
 }