libs/binder/RpcConnection.cpp - android_frameworks_native - Gitiles

 /*
  * Copyright (C) 2020 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
  *
  *      http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */

 #define LOG_TAG "RpcConnection"

 #include <binder/RpcConnection.h>

 #include <binder/Parcel.h>
 #include <binder/Stability.h>
 #include <utils/String8.h>

 #include "RpcState.h"
 #include "RpcWireFormat.h"

 #include <sys/socket.h>
 #include <sys/types.h>
 #include <sys/un.h>
 #include <unistd.h>

 #ifdef __GLIBC__
 extern "C" pid_t gettid();
 #endif

 #ifdef __BIONIC__
 #include <linux/vm_sockets.h>
 #endif

 namespace android {

 using base::unique_fd;

 RpcConnection::SocketAddress::~SocketAddress() {}

 RpcConnection::RpcConnection() {
     LOG_RPC_DETAIL("RpcConnection created %p", this);

     mState = std::make_unique<RpcState>();
 }
 RpcConnection::~RpcConnection() {
     LOG_RPC_DETAIL("RpcConnection destroyed %p", this);
 }

 sp<RpcConnection> RpcConnection::make() {
     return new RpcConnection;
 }

 class UnixSocketAddress : public RpcConnection::SocketAddress {
 public:
     explicit UnixSocketAddress(const char* path) : mAddr({.sun_family = AF_UNIX}) {
         unsigned int pathLen = strlen(path) + 1;
         LOG_ALWAYS_FATAL_IF(pathLen > sizeof(mAddr.sun_path), "%u %s", pathLen, path);
         memcpy(mAddr.sun_path, path, pathLen);
     }
     virtual ~UnixSocketAddress() {}
     std::string toString() const override {
         return String8::format("path '%.*s'", static_cast<int>(sizeof(mAddr.sun_path)),
                                mAddr.sun_path)
                 .c_str();
     }
     const sockaddr* addr() const override { return reinterpret_cast<const sockaddr*>(&mAddr); }
     size_t addrSize() const override { return sizeof(mAddr); }

 private:
     sockaddr_un mAddr;
 };

 bool RpcConnection::setupUnixDomainServer(const char* path) {
     return addServer(UnixSocketAddress(path));
 }

 bool RpcConnection::addUnixDomainClient(const char* path) {
     return addClient(UnixSocketAddress(path));
 }

 #ifdef __BIONIC__

 class VsockSocketAddress : public RpcConnection::SocketAddress {
 public:
     VsockSocketAddress(unsigned int cid, unsigned int port)
           : mAddr({
                     .svm_family = AF_VSOCK,
                     .svm_port = port,
                     .svm_cid = cid,
             }) {}
     virtual ~VsockSocketAddress() {}
     std::string toString() const override {
         return String8::format("cid %du port %du", mAddr.svm_cid, mAddr.svm_port).c_str();
     }
     const sockaddr* addr() const override { return reinterpret_cast<const sockaddr*>(&mAddr); }
     size_t addrSize() const override { return sizeof(mAddr); }

 private:
     sockaddr_vm mAddr;
 };

 bool RpcConnection::setupVsockServer(unsigned int port) {
     // realizing value w/ this type at compile time to avoid ubsan abort
     constexpr unsigned int kAnyCid = VMADDR_CID_ANY;

     return addServer(VsockSocketAddress(kAnyCid, port));
 }

 bool RpcConnection::addVsockClient(unsigned int cid, unsigned int port) {
     return addClient(VsockSocketAddress(cid, port));
 }

 #endif // __BIONIC__

 sp<IBinder> RpcConnection::getRootObject() {
     ExclusiveSocket socket(this, SocketUse::CLIENT);
     return state()->getRootObject(socket.fd(), this);
 }

 status_t RpcConnection::transact(const RpcAddress& address, uint32_t code, const Parcel& data,
                                  Parcel* reply, uint32_t flags) {
     ExclusiveSocket socket(this,
                            (flags & IBinder::FLAG_ONEWAY) ? SocketUse::CLIENT_ASYNC
                                                           : SocketUse::CLIENT);
     return state()->transact(socket.fd(), address, code, data, this, reply, flags);
 }

 status_t RpcConnection::sendDecStrong(const RpcAddress& address) {
     ExclusiveSocket socket(this, SocketUse::CLIENT_REFCOUNT);
     return state()->sendDecStrong(socket.fd(), address);
 }

 void RpcConnection::join() {
     // establish a connection
     {
         unique_fd clientFd(
                 TEMP_FAILURE_RETRY(accept4(mServer.get(), nullptr, 0 /*length*/, SOCK_CLOEXEC)));
         if (clientFd < 0) {
             // If this log becomes confusing, should save more state from setupUnixDomainServer
             // in order to output here.
             ALOGE("Could not accept4 socket: %s", strerror(errno));
             return;
         }

         LOG_RPC_DETAIL("accept4 on fd %d yields fd %d", mServer.get(), clientFd.get());

         assignServerToThisThread(std::move(clientFd));
     }

     // We may not use the connection we just established (two threads might
     // establish connections for each other), but for now, just use one
     // server/socket connection.
     ExclusiveSocket socket(this, SocketUse::SERVER);

     while (true) {
         status_t error = state()->getAndExecuteCommand(socket.fd(), this);

         if (error != OK) {
             ALOGI("Binder socket thread closing w/ status %s", statusToString(error).c_str());
             return;
         }
     }
 }

 void RpcConnection::setForServer(const wp<RpcServer>& server) {
     mForServer = server;
 }

 wp<RpcServer> RpcConnection::server() {
     return mForServer;
 }

 bool RpcConnection::addServer(const SocketAddress& addr) {
     LOG_ALWAYS_FATAL_IF(mServer.get() != -1, "Each RpcConnection can only have one server.");

     unique_fd serverFd(
             TEMP_FAILURE_RETRY(socket(addr.addr()->sa_family, SOCK_STREAM | SOCK_CLOEXEC, 0)));
     if (serverFd == -1) {
         ALOGE("Could not create socket: %s", strerror(errno));
         return false;
     }

     if (0 != TEMP_FAILURE_RETRY(bind(serverFd.get(), addr.addr(), addr.addrSize()))) {
         int savedErrno = errno;
         ALOGE("Could not bind socket at %s: %s", addr.toString().c_str(), strerror(savedErrno));
         return false;
     }

     if (0 != TEMP_FAILURE_RETRY(listen(serverFd.get(), 1 /*backlog*/))) {
         int savedErrno = errno;
         ALOGE("Could not listen socket at %s: %s", addr.toString().c_str(), strerror(savedErrno));
         return false;
     }

     mServer = std::move(serverFd);
     return true;
 }

 bool RpcConnection::addClient(const SocketAddress& addr) {
     unique_fd serverFd(
             TEMP_FAILURE_RETRY(socket(addr.addr()->sa_family, SOCK_STREAM | SOCK_CLOEXEC, 0)));
     if (serverFd == -1) {
         int savedErrno = errno;
         ALOGE("Could not create socket at %s: %s", addr.toString().c_str(), strerror(savedErrno));
         return false;
     }

     if (0 != TEMP_FAILURE_RETRY(connect(serverFd.get(), addr.addr(), addr.addrSize()))) {
         int savedErrno = errno;
         ALOGE("Could not connect socket at %s: %s", addr.toString().c_str(), strerror(savedErrno));
         return false;
     }

     LOG_RPC_DETAIL("Socket at %s client with fd %d", addr.toString().c_str(), serverFd.get());

     std::lock_guard<std::mutex> _l(mSocketMutex);
     sp<ConnectionSocket> connection = new ConnectionSocket();
     connection->fd = std::move(serverFd);
     mClients.push_back(connection);
     return true;
 }

 void RpcConnection::assignServerToThisThread(base::unique_fd&& fd) {
     std::lock_guard<std::mutex> _l(mSocketMutex);
     sp<ConnectionSocket> connection = new ConnectionSocket();
     connection->fd = std::move(fd);
     mServers.push_back(connection);
 }

 RpcConnection::ExclusiveSocket::ExclusiveSocket(const sp<RpcConnection>& connection, SocketUse use)
       : mConnection(connection) {
     pid_t tid = gettid();
     std::unique_lock<std::mutex> _l(mConnection->mSocketMutex);

     mConnection->mWaitingThreads++;
     while (true) {
         sp<ConnectionSocket> exclusive;
         sp<ConnectionSocket> available;

         // CHECK FOR DEDICATED CLIENT SOCKET
         //
         // A server/looper should always use a dedicated connection.
         if (use != SocketUse::SERVER) {
             findSocket(tid, &exclusive, &available, mConnection->mClients,
                        mConnection->mClientsOffset);

             // WARNING: this assumes a server cannot request its client to send
             // a transaction, as mServers is excluded below.
             //
             // Imagine we have more than one thread in play, and a single thread
             // sends a synchronous, then an asynchronous command. Imagine the
             // asynchronous command is sent on the first client socket. Then, if
             // we naively send a synchronous command to that same socket, the
             // thread on the far side might be busy processing the asynchronous
             // command. So, we move to considering the second available thread
             // for subsequent calls.
             if (use == SocketUse::CLIENT_ASYNC && (exclusive != nullptr || available != nullptr)) {
                 mConnection->mClientsOffset =
                         (mConnection->mClientsOffset + 1) % mConnection->mClients.size();
             }
         }

         // USE SERVING SOCKET (to start serving or for nested transaction)
         //
         // asynchronous calls cannot be nested
         if (use != SocketUse::CLIENT_ASYNC) {
             // servers should start serving on an available thread only
             // otherwise, this should only be a nested call
             bool useAvailable = use == SocketUse::SERVER;

             findSocket(tid, &exclusive, (useAvailable ? &available : nullptr),
                        mConnection->mServers, 0 /* index hint */);
         }

         // if our thread is already using a connection, prioritize using that
         if (exclusive != nullptr) {
             mSocket = exclusive;
             mReentrant = true;
             break;
         } else if (available != nullptr) {
             mSocket = available;
             mSocket->exclusiveTid = tid;
             break;
         }

         LOG_ALWAYS_FATAL_IF(use == SocketUse::SERVER, "Must create connection to join one.");

         // in regular binder, this would usually be a deadlock :)
         LOG_ALWAYS_FATAL_IF(mConnection->mClients.size() == 0,
                             "Not a client of any connection. You must create a connection to an "
                             "RPC server to make any non-nested (e.g. oneway or on another thread) "
                             "calls.");

         LOG_RPC_DETAIL("No available connection (have %zu clients and %zu servers). Waiting...",
                        mConnection->mClients.size(), mConnection->mServers.size());
         mConnection->mSocketCv.wait(_l);
     }
     mConnection->mWaitingThreads--;
 }

 void RpcConnection::ExclusiveSocket::findSocket(pid_t tid, sp<ConnectionSocket>* exclusive,
                                                 sp<ConnectionSocket>* available,
                                                 std::vector<sp<ConnectionSocket>>& sockets,
                                                 size_t socketsIndexHint) {
     LOG_ALWAYS_FATAL_IF(sockets.size() > 0 && socketsIndexHint >= sockets.size(),
                         "Bad index %zu >= %zu", socketsIndexHint, sockets.size());

     if (*exclusive != nullptr) return; // consistent with break below

     for (size_t i = 0; i < sockets.size(); i++) {
         sp<ConnectionSocket>& socket = sockets[(i + socketsIndexHint) % sockets.size()];

         // take first available connection (intuition = caching)
         if (available && *available == nullptr && socket->exclusiveTid == std::nullopt) {
             *available = socket;
             continue;
         }

         // though, prefer to take connection which is already inuse by this thread
         // (nested transactions)
         if (exclusive && socket->exclusiveTid == tid) {
             *exclusive = socket;
             break; // consistent with return above
         }
     }
 }

 RpcConnection::ExclusiveSocket::~ExclusiveSocket() {
     // reentrant use of a connection means something less deep in the call stack
     // is using this fd, and it retains the right to it. So, we don't give up
     // exclusive ownership, and no thread is freed.
     if (!mReentrant) {
         std::unique_lock<std::mutex> _l(mConnection->mSocketMutex);
         mSocket->exclusiveTid = std::nullopt;
         if (mConnection->mWaitingThreads > 0) {
             _l.unlock();
             mConnection->mSocketCv.notify_one();
         }
     }
 }

 } // namespace android
	/*
	* Copyright (C) 2020 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
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/

	#define LOG_TAG "RpcConnection"

	#include <binder/RpcConnection.h>

	#include <binder/Parcel.h>
	#include <binder/Stability.h>
	#include <utils/String8.h>

	#include "RpcState.h"
	#include "RpcWireFormat.h"

	#include <sys/socket.h>
	#include <sys/types.h>
	#include <sys/un.h>
	#include <unistd.h>

	#ifdef __GLIBC__
	extern "C" pid_t gettid();
	#endif

	#ifdef __BIONIC__
	#include <linux/vm_sockets.h>
	#endif

	namespace android {

	using base::unique_fd;

	RpcConnection::SocketAddress::~SocketAddress() {}

	RpcConnection::RpcConnection() {
	LOG_RPC_DETAIL("RpcConnection created %p", this);

	mState = std::make_unique<RpcState>();
	}
	RpcConnection::~RpcConnection() {
	LOG_RPC_DETAIL("RpcConnection destroyed %p", this);
	}

	sp<RpcConnection> RpcConnection::make() {
	return new RpcConnection;
	}

	class UnixSocketAddress : public RpcConnection::SocketAddress {
	public:
	explicit UnixSocketAddress(const char* path) : mAddr({.sun_family = AF_UNIX}) {
	unsigned int pathLen = strlen(path) + 1;
	LOG_ALWAYS_FATAL_IF(pathLen > sizeof(mAddr.sun_path), "%u %s", pathLen, path);
	memcpy(mAddr.sun_path, path, pathLen);
	}
	virtual ~UnixSocketAddress() {}
	std::string toString() const override {
	return String8::format("path '%.*s'", static_cast<int>(sizeof(mAddr.sun_path)),
	mAddr.sun_path)
	.c_str();
	}
	const sockaddr* addr() const override { return reinterpret_cast<const sockaddr*>(&mAddr); }
	size_t addrSize() const override { return sizeof(mAddr); }

	private:
	sockaddr_un mAddr;
	};

	bool RpcConnection::setupUnixDomainServer(const char* path) {
	return addServer(UnixSocketAddress(path));
	}

	bool RpcConnection::addUnixDomainClient(const char* path) {
	return addClient(UnixSocketAddress(path));
	}

	#ifdef __BIONIC__

	class VsockSocketAddress : public RpcConnection::SocketAddress {
	public:
	VsockSocketAddress(unsigned int cid, unsigned int port)
	: mAddr({
	.svm_family = AF_VSOCK,
	.svm_port = port,
	.svm_cid = cid,
	}) {}
	virtual ~VsockSocketAddress() {}
	std::string toString() const override {
	return String8::format("cid %du port %du", mAddr.svm_cid, mAddr.svm_port).c_str();
	}
	const sockaddr* addr() const override { return reinterpret_cast<const sockaddr*>(&mAddr); }
	size_t addrSize() const override { return sizeof(mAddr); }

	private:
	sockaddr_vm mAddr;
	};

	bool RpcConnection::setupVsockServer(unsigned int port) {
	// realizing value w/ this type at compile time to avoid ubsan abort
	constexpr unsigned int kAnyCid = VMADDR_CID_ANY;

	return addServer(VsockSocketAddress(kAnyCid, port));
	}

	bool RpcConnection::addVsockClient(unsigned int cid, unsigned int port) {
	return addClient(VsockSocketAddress(cid, port));
	}

	#endif // __BIONIC__

	sp<IBinder> RpcConnection::getRootObject() {
	ExclusiveSocket socket(this, SocketUse::CLIENT);
	return state()->getRootObject(socket.fd(), this);
	}

	status_t RpcConnection::transact(const RpcAddress& address, uint32_t code, const Parcel& data,
	Parcel* reply, uint32_t flags) {
	ExclusiveSocket socket(this,
	(flags & IBinder::FLAG_ONEWAY) ? SocketUse::CLIENT_ASYNC
	: SocketUse::CLIENT);
	return state()->transact(socket.fd(), address, code, data, this, reply, flags);
	}

	status_t RpcConnection::sendDecStrong(const RpcAddress& address) {
	ExclusiveSocket socket(this, SocketUse::CLIENT_REFCOUNT);
	return state()->sendDecStrong(socket.fd(), address);
	}

	void RpcConnection::join() {
	// establish a connection
	{
	unique_fd clientFd(
	TEMP_FAILURE_RETRY(accept4(mServer.get(), nullptr, 0 /length/, SOCK_CLOEXEC)));
	if (clientFd < 0) {
	// If this log becomes confusing, should save more state from setupUnixDomainServer
	// in order to output here.
	ALOGE("Could not accept4 socket: %s", strerror(errno));
	return;
	}

	LOG_RPC_DETAIL("accept4 on fd %d yields fd %d", mServer.get(), clientFd.get());

	assignServerToThisThread(std::move(clientFd));
	}

	// We may not use the connection we just established (two threads might
	// establish connections for each other), but for now, just use one
	// server/socket connection.
	ExclusiveSocket socket(this, SocketUse::SERVER);

	while (true) {
	status_t error = state()->getAndExecuteCommand(socket.fd(), this);

	if (error != OK) {
	ALOGI("Binder socket thread closing w/ status %s", statusToString(error).c_str());
	return;
	}
	}
	}

	void RpcConnection::setForServer(const wp<RpcServer>& server) {
	mForServer = server;
	}

	wp<RpcServer> RpcConnection::server() {
	return mForServer;
	}

	bool RpcConnection::addServer(const SocketAddress& addr) {
	LOG_ALWAYS_FATAL_IF(mServer.get() != -1, "Each RpcConnection can only have one server.");

	unique_fd serverFd(
	TEMP_FAILURE_RETRY(socket(addr.addr()->sa_family, SOCK_STREAM \| SOCK_CLOEXEC, 0)));
	if (serverFd == -1) {
	ALOGE("Could not create socket: %s", strerror(errno));
	return false;
	}

	if (0 != TEMP_FAILURE_RETRY(bind(serverFd.get(), addr.addr(), addr.addrSize()))) {
	int savedErrno = errno;
	ALOGE("Could not bind socket at %s: %s", addr.toString().c_str(), strerror(savedErrno));
	return false;
	}

	if (0 != TEMP_FAILURE_RETRY(listen(serverFd.get(), 1 /backlog/))) {
	int savedErrno = errno;
	ALOGE("Could not listen socket at %s: %s", addr.toString().c_str(), strerror(savedErrno));
	return false;
	}

	mServer = std::move(serverFd);
	return true;
	}

	bool RpcConnection::addClient(const SocketAddress& addr) {
	unique_fd serverFd(
	TEMP_FAILURE_RETRY(socket(addr.addr()->sa_family, SOCK_STREAM \| SOCK_CLOEXEC, 0)));
	if (serverFd == -1) {
	int savedErrno = errno;
	ALOGE("Could not create socket at %s: %s", addr.toString().c_str(), strerror(savedErrno));
	return false;
	}

	if (0 != TEMP_FAILURE_RETRY(connect(serverFd.get(), addr.addr(), addr.addrSize()))) {
	int savedErrno = errno;
	ALOGE("Could not connect socket at %s: %s", addr.toString().c_str(), strerror(savedErrno));
	return false;
	}

	LOG_RPC_DETAIL("Socket at %s client with fd %d", addr.toString().c_str(), serverFd.get());

	std::lock_guard<std::mutex> _l(mSocketMutex);
	sp<ConnectionSocket> connection = new ConnectionSocket();
	connection->fd = std::move(serverFd);
	mClients.push_back(connection);
	return true;
	}

	void RpcConnection::assignServerToThisThread(base::unique_fd&& fd) {
	std::lock_guard<std::mutex> _l(mSocketMutex);
	sp<ConnectionSocket> connection = new ConnectionSocket();
	connection->fd = std::move(fd);
	mServers.push_back(connection);
	}

	RpcConnection::ExclusiveSocket::ExclusiveSocket(const sp<RpcConnection>& connection, SocketUse use)
	: mConnection(connection) {
	pid_t tid = gettid();
	std::unique_lock<std::mutex> _l(mConnection->mSocketMutex);

	mConnection->mWaitingThreads++;
	while (true) {
	sp<ConnectionSocket> exclusive;
	sp<ConnectionSocket> available;

	// CHECK FOR DEDICATED CLIENT SOCKET
	//
	// A server/looper should always use a dedicated connection.
	if (use != SocketUse::SERVER) {
	findSocket(tid, &exclusive, &available, mConnection->mClients,
	mConnection->mClientsOffset);

	// WARNING: this assumes a server cannot request its client to send
	// a transaction, as mServers is excluded below.
	//
	// Imagine we have more than one thread in play, and a single thread
	// sends a synchronous, then an asynchronous command. Imagine the
	// asynchronous command is sent on the first client socket. Then, if
	// we naively send a synchronous command to that same socket, the
	// thread on the far side might be busy processing the asynchronous
	// command. So, we move to considering the second available thread
	// for subsequent calls.
	if (use == SocketUse::CLIENT_ASYNC && (exclusive != nullptr \|\| available != nullptr)) {
	mConnection->mClientsOffset =
	(mConnection->mClientsOffset + 1) % mConnection->mClients.size();
	}
	}

	// USE SERVING SOCKET (to start serving or for nested transaction)
	//
	// asynchronous calls cannot be nested
	if (use != SocketUse::CLIENT_ASYNC) {
	// servers should start serving on an available thread only
	// otherwise, this should only be a nested call
	bool useAvailable = use == SocketUse::SERVER;

	findSocket(tid, &exclusive, (useAvailable ? &available : nullptr),
	mConnection->mServers, 0 /* index hint */);
	}

	// if our thread is already using a connection, prioritize using that
	if (exclusive != nullptr) {
	mSocket = exclusive;
	mReentrant = true;
	break;
	} else if (available != nullptr) {
	mSocket = available;
	mSocket->exclusiveTid = tid;
	break;
	}

	LOG_ALWAYS_FATAL_IF(use == SocketUse::SERVER, "Must create connection to join one.");

	// in regular binder, this would usually be a deadlock :)
	LOG_ALWAYS_FATAL_IF(mConnection->mClients.size() == 0,
	"Not a client of any connection. You must create a connection to an "
	"RPC server to make any non-nested (e.g. oneway or on another thread) "
	"calls.");

	LOG_RPC_DETAIL("No available connection (have %zu clients and %zu servers). Waiting...",
	mConnection->mClients.size(), mConnection->mServers.size());
	mConnection->mSocketCv.wait(_l);
	}
	mConnection->mWaitingThreads--;
	}

	void RpcConnection::ExclusiveSocket::findSocket(pid_t tid, sp<ConnectionSocket>* exclusive,
	sp<ConnectionSocket>* available,
	std::vector<sp<ConnectionSocket>>& sockets,
	size_t socketsIndexHint) {
	LOG_ALWAYS_FATAL_IF(sockets.size() > 0 && socketsIndexHint >= sockets.size(),
	"Bad index %zu >= %zu", socketsIndexHint, sockets.size());

	if (*exclusive != nullptr) return; // consistent with break below

	for (size_t i = 0; i < sockets.size(); i++) {
	sp<ConnectionSocket>& socket = sockets[(i + socketsIndexHint) % sockets.size()];

	// take first available connection (intuition = caching)
	if (available && *available == nullptr && socket->exclusiveTid == std::nullopt) {
	*available = socket;
	continue;
	}

	// though, prefer to take connection which is already inuse by this thread
	// (nested transactions)
	if (exclusive && socket->exclusiveTid == tid) {
	*exclusive = socket;
	break; // consistent with return above
	}
	}
	}

	RpcConnection::ExclusiveSocket::~ExclusiveSocket() {
	// reentrant use of a connection means something less deep in the call stack
	// is using this fd, and it retains the right to it. So, we don't give up
	// exclusive ownership, and no thread is freed.
	if (!mReentrant) {
	std::unique_lock<std::mutex> _l(mConnection->mSocketMutex);
	mSocket->exclusiveTid = std::nullopt;
	if (mConnection->mWaitingThreads > 0) {
	_l.unlock();
	mConnection->mSocketCv.notify_one();
	}
	}
	}

	} // namespace android