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* Copyright (C) 2022 The Android Open Source Project
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* See the License for the specific language governing permissions and
* limitations under the License.
#include <android/binder_auto_utils.h>
#include <android/binder_ibinder.h>
#include <binder/Parcel.h>
#include <list>
namespace android::frameworks::cameraservice::utils {
* This is a helper class to pipe death notifications from VNDK {@code AIBinder} to
* S/NDK {@code IBinder}.
* To use this class, create a DeathPipe member object as a field of NDK interface
* implementation, and forward functions {@code BBinder::linkToDeath} and
* {@code BBinder::unlinkToDeath} to corresponding DeathPipe functions.
class DeathPipe {
* @param parent the NDK Binder object. Assumed to live longer than the DeathPipe
* object
* @param binder the VNDK Binder object which DeathPipe with subscribe to.
explicit DeathPipe(IBinder* parent, const ::ndk::SpAIBinder& binder);
status_t linkToDeath(const sp<IBinder::DeathRecipient>& recipient, void* cookie,
uint32_t flags);
status_t unlinkToDeath(const wp<IBinder::DeathRecipient>& recipient,
void* cookie, uint32_t flags, wp<IBinder::DeathRecipient>* outRecipient);
// Static functions that will be called by VNDK binder upon death or unlinking
static void onDeathCallback(void* cookie);
static void onUnlinkedCallback(void* cookie);
* {@code Obituary} is a tiny container that contains some metadata to pass VNDK binder's
* death notification to the NDK binder. A pointer to the Obituary is used as the
* {@code cookie} in VNDK binder's death notification.
* Theoretically, the VNDK binder might send out death notification after the DeathPipe
* object is destroyed, so care must be taken to ensure that Obituaries aren't accidentally
* destroyed before VNDK binder stops using its cookies.
struct Obituary: public std::enable_shared_from_this<Obituary> {
wp<IBinder::DeathRecipient> recipient; // NDK death recipient
void *cookie; // cookie sent by the NDK recipient
uint32_t flags; // flags sent by the NDK recipient
wp<IBinder> who; // NDK binder whose death 'recipient' subscribed to
// Self ptr to ensure we don't destroy this obituary while it can still be notified by the
// VNDK Binder. When populated with Obituary::immortalize, this Obituary won't be
// garbage collected until Obituary::clear is called.
std::shared_ptr<Obituary> mSelfPtr;
Obituary(const wp<IBinder::DeathRecipient>& recipient, void* cookie,
uint32_t flags, IBinder* who) :
recipient(recipient), cookie(cookie), flags(flags),
who(who), mSelfPtr(nullptr) {}
// Function to be called when the VNDK Binder dies. Pipes the notification to the relevant
// NDK recipient if it still exists
void onDeath() const {
sp<IBinder::DeathRecipient> r = recipient.promote();
if (r == nullptr) { return; }
// Should be called before calling AIBinder_linkToDeath. Once this function returns this
// Obituary won't be garbage collected until Obituary::clear is called.
void immortalize() {
mSelfPtr = shared_from_this();
// Should be called when this Obituary can be garbage collected.
// Typically, after the Obituary is no longer linked to a VNDK DeathRecipient
void clear() {
mSelfPtr = nullptr;
bool operator==(const Obituary& rhs) const {
return recipient == rhs.recipient &&
cookie == rhs.cookie &&
flags == rhs.flags &&
who == rhs.who;
// Parent to which the cameraservice wants to subscribe to for death notification
IBinder* mParent;
// VNDK Binder object to which the death notification will be bound to. If it dies,
// cameraservice will be notified as if mParent died.
::ndk::SpAIBinder mAIBinder;
// Owning VNDK's deathRecipient ensures that all linked death notifications are cleaned up
// when this class destructs.
::ndk::ScopedAIBinder_DeathRecipient mDeathRecipient;
// Lock to protect access to fields below.
std::mutex mLock;
// List of all obituaries created by DeathPipe, used to unlink death subscription
std::list<std::shared_ptr<Obituary>> mObituaries;
} // namespace android::frameworks::cameraservice::utils