libbinder: avoid global mutex every binder call
We can't get rid of a mutex (or similar) for the rarer
ProcessState::selfOrNull access, but for ProcessState::self() accesses,
which happen at least once every binder call, we can use the very fast
once flags.
Bug: 161336582
Test: boots
Change-Id: I66fee6be0260f59f80a85328228776de7e68c7fb
diff --git a/libs/binder/ProcessState.cpp b/libs/binder/ProcessState.cpp
index 0f81e0b..02e0193 100644
--- a/libs/binder/ProcessState.cpp
+++ b/libs/binder/ProcessState.cpp
@@ -32,6 +32,7 @@
#include <errno.h>
#include <fcntl.h>
+#include <mutex>
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
@@ -73,38 +74,49 @@
sp<ProcessState> ProcessState::self()
{
- Mutex::Autolock _l(gProcessMutex);
- if (gProcess != nullptr) {
- return gProcess;
- }
- gProcess = new ProcessState(kDefaultDriver);
- return gProcess;
+ return init(kDefaultDriver, false /*requireDefault*/);
}
sp<ProcessState> ProcessState::initWithDriver(const char* driver)
{
- Mutex::Autolock _l(gProcessMutex);
- if (gProcess != nullptr) {
- // Allow for initWithDriver to be called repeatedly with the same
- // driver.
- if (!strcmp(gProcess->getDriverName().c_str(), driver)) {
- return gProcess;
- }
- LOG_ALWAYS_FATAL("ProcessState was already initialized.");
- }
-
- if (access(driver, R_OK) == -1) {
- ALOGE("Binder driver %s is unavailable. Using /dev/binder instead.", driver);
- driver = "/dev/binder";
- }
-
- gProcess = new ProcessState(driver);
- return gProcess;
+ return init(driver, true /*requireDefault*/);
}
sp<ProcessState> ProcessState::selfOrNull()
{
- Mutex::Autolock _l(gProcessMutex);
+ return init(nullptr, false /*requireDefault*/);
+}
+
+sp<ProcessState> ProcessState::init(const char *driver, bool requireDefault)
+{
+ [[clang::no_destroy]] static sp<ProcessState> gProcess;
+ [[clang::no_destroy]] static std::mutex gProcessMutex;
+
+ if (driver == nullptr) {
+ std::lock_guard<std::mutex> l(gProcessMutex);
+ return gProcess;
+ }
+
+ [[clang::no_destroy]] static std::once_flag gProcessOnce;
+ std::call_once(gProcessOnce, [&](){
+ if (access(driver, R_OK) == -1) {
+ ALOGE("Binder driver %s is unavailable. Using /dev/binder instead.", driver);
+ driver = "/dev/binder";
+ }
+
+ std::lock_guard<std::mutex> l(gProcessMutex);
+ gProcess = new ProcessState(driver);
+ });
+
+ if (requireDefault) {
+ // Detect if we are trying to initialize with a different driver, and
+ // consider that an error. ProcessState will only be initialized once above.
+ LOG_ALWAYS_FATAL_IF(gProcess->getDriverName() != driver,
+ "ProcessState was already initialized with %s,"
+ " can't initialize with %s.",
+ gProcess->getDriverName().c_str(), driver);
+ }
+
return gProcess;
}