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Commit 1f1bed66 authored by Steven Moreland's avatar Steven Moreland
Browse files

libbinder_ndk: eradicate global lock 

Let the nightmares cease!
Without contention, peace.

Note, in the case that an ABpBinder is backed by a BBinder (this happens
when you talk in-process to something between the NDK backend and either
the C++, Rust, or Java backends of AIDL), this introduces an additional
allocation b/c the BBinder's mExtra needs to be allocated for
BBinder::withLock to work. Since this is generally frowned upon, and the
thrashing in this case is already pretty egregious, I don't mind it.
Now, binder proxies can be allocated simultaneously in a process.

Bug: 192023359
Test: CtsNdkBinderTestCases
Change-Id: Ib1c28c9488f7a03579ea9d18347a8fc08cc3f48a
parent 9e759e81

libs/binder/ndk/ibinder.cpp

+18 −14
Original line number Diff line number Diff line
@@ -57,7 +57,6 @@ static bool has(const sp<IBinder>& binder) { 


namespace ABpBinderTag {



static std::mutex gLock;

static const void* kId = "ABpBinder";

struct Value {

    wp<ABpBinder> binder;
@@ -252,23 +251,28 @@ sp<AIBinder> ABpBinder::lookupOrCreateFromBinder(const ::android::sp<::android:: 
        return static_cast<ABBinder*>(binder.get());

    }



    // The following code ensures that for a given binder object (remote or local), if it is not an

    // ABBinder then at most one ABpBinder object exists in a given process representing it.

    std::lock_guard<std::mutex> lock(ABpBinderTag::gLock);



    ABpBinderTag::Value* value =

            static_cast<ABpBinderTag::Value*>(binder->findObject(ABpBinderTag::kId));

    auto* value = static_cast<ABpBinderTag::Value*>(binder->findObject(ABpBinderTag::kId));

    if (value == nullptr) {

        value = new ABpBinderTag::Value;

        binder->attachObject(ABpBinderTag::kId, static_cast<void*>(value), nullptr /*cookie*/,

                             ABpBinderTag::clean);

        auto oldValue = static_cast<ABpBinderTag::Value*>(

                binder->attachObject(ABpBinderTag::kId, static_cast<void*>(value),

                                     nullptr /*cookie*/, ABpBinderTag::clean));



        // allocated by another thread

        if (oldValue) {

            delete value;

            value = oldValue;

        }

    }



    sp<ABpBinder> ret = value->binder.promote();

    sp<ABpBinder> ret;

    binder->withLock([&]() {

        ret = value->binder.promote();

        if (ret == nullptr) {

        ret = new ABpBinder(binder);

            ret = sp<ABpBinder>::make(binder);

            value->binder = ret;

        }

    });



    return ret;

}

libs/binder/ndk/ibinder_internal.h

+1 −0
Original line number Diff line number Diff line
@@ -105,6 +105,7 @@ struct ABpBinder : public AIBinder, public ::android::BpRefBase { 
    ABpBinder* asABpBinder() override { return this; }



   private:

    friend android::sp<ABpBinder>;

    explicit ABpBinder(const ::android::sp<::android::IBinder>& binder);

};