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Commit 4fdb12f6 authored by Steven Moreland's avatar Steven Moreland
Browse files

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
parent ea830510

libs/binder/ProcessState.cpp

+36 −24
Original line number Diff line number Diff line
@@ -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 @@ protected: 


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;

    return init(driver, true /*requireDefault*/);

}



sp<ProcessState> ProcessState::selfOrNull()

{

    return init(nullptr, false /*requireDefault*/);

}

        LOG_ALWAYS_FATAL("ProcessState was already initialized.");



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);

    return gProcess;

    });



    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);

    }



sp<ProcessState> ProcessState::selfOrNull()

{

    Mutex::Autolock _l(gProcessMutex);

    return gProcess;

}

libs/binder/Static.cpp

+0 −5
Original line number Diff line number Diff line
@@ -68,9 +68,4 @@ TextOutput& alog(*new LogTextOutput()); 
TextOutput& aout(*new FdTextOutput(STDOUT_FILENO));

TextOutput& aerr(*new FdTextOutput(STDERR_FILENO));



// ------------ ProcessState.cpp



Mutex& gProcessMutex = *new Mutex;

sp<ProcessState> gProcess;



}   // namespace android

libs/binder/Static.h

+0 −4
Original line number Diff line number Diff line
@@ -27,8 +27,4 @@ namespace android { 
// For TextStream.cpp

extern Vector<int32_t> gTextBuffers;



// For ProcessState.cpp

extern Mutex& gProcessMutex;

extern sp<ProcessState> gProcess;



}   // namespace android

libs/binder/include/binder/ProcessState.h

+4 −0
Original line number Diff line number Diff line
@@ -42,6 +42,8 @@ public: 
     * any call to ProcessState::self(). The default is /dev/vndbinder

     * for processes built with the VNDK and /dev/binder for those

     * which are not.

     *

     * If this is called with nullptr, the behavior is the same as selfOrNull.

     */

    static  sp<ProcessState>    initWithDriver(const char *driver);
@@ -90,6 +92,8 @@ public: 
            void setCallRestriction(CallRestriction restriction);



private:

    static  sp<ProcessState>    init(const char *defaultDriver, bool requireDefault);



    friend class IPCThreadState;

    

            explicit            ProcessState(const char* driver);