libbinder: RPC socket bound to service thread
This is in preparation of transforming binder RPC to have a more
traditional server achitecture where the server accepts new connections,
and arbitrarily many can be added.
Before this change, there were a few issues:
- threads might call accept, but not use the FD they accepted (threads
would accidentally trade FDs, and this could create confusing logs)
- if a server thread disconnected or finished, another thread might try
to reuse the FD being used there
Now:
- server sockets are associated with the thread from the beginning
- when a connection disconnects, the server also removes the connection
Bug: 185167543
Test: binderRpcTest (note added ~RpcConnection assert)
Change-Id: Icf50a23ba52167c6fbe04ad1a77cfcb6fb3fcc9c
diff --git a/libs/binder/RpcConnection.cpp b/libs/binder/RpcConnection.cpp
index 22e0466..1388a80 100644
--- a/libs/binder/RpcConnection.cpp
+++ b/libs/binder/RpcConnection.cpp
@@ -57,6 +57,10 @@
}
RpcConnection::~RpcConnection() {
LOG_RPC_DETAIL("RpcConnection destroyed %p", this);
+
+ std::lock_guard<std::mutex> _l(mSocketMutex);
+ LOG_ALWAYS_FATAL_IF(mServers.size() != 0,
+ "Should not be able to destroy a connection with servers in use.");
}
sp<RpcConnection> RpcConnection::make() {
@@ -222,36 +226,35 @@
}
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));
+ // TODO(b/185167543): do this dynamically, instead of from a static number
+ // of threads
+ 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;
}
- // 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(sp<RpcConnection>::fromExisting(this), SocketUse::SERVER);
+ LOG_RPC_DETAIL("accept4 on fd %d yields fd %d", mServer.get(), clientFd.get());
+
+ // must be registered to allow arbitrary client code executing commands to
+ // be able to do nested calls (we can't only read from it)
+ sp<ConnectionSocket> socket = assignServerToThisThread(std::move(clientFd));
while (true) {
status_t error =
- state()->getAndExecuteCommand(socket.fd(), sp<RpcConnection>::fromExisting(this));
+ state()->getAndExecuteCommand(socket->fd, sp<RpcConnection>::fromExisting(this));
if (error != OK) {
ALOGI("Binder socket thread closing w/ status %s", statusToString(error).c_str());
- return;
+ break;
}
}
+
+ LOG_ALWAYS_FATAL_IF(!removeServerSocket(socket),
+ "bad state: socket object guaranteed to be in list");
}
void RpcConnection::setForServer(const wp<RpcServer>& server) {
@@ -316,11 +319,23 @@
mClients.push_back(connection);
}
-void RpcConnection::assignServerToThisThread(unique_fd&& fd) {
+sp<RpcConnection::ConnectionSocket> RpcConnection::assignServerToThisThread(unique_fd&& fd) {
std::lock_guard<std::mutex> _l(mSocketMutex);
sp<ConnectionSocket> connection = sp<ConnectionSocket>::make();
connection->fd = std::move(fd);
+ connection->exclusiveTid = gettid();
mServers.push_back(connection);
+
+ return connection;
+}
+
+bool RpcConnection::removeServerSocket(const sp<ConnectionSocket>& socket) {
+ std::lock_guard<std::mutex> _l(mSocketMutex);
+ if (auto it = std::find(mServers.begin(), mServers.end(), socket); it != mServers.end()) {
+ mServers.erase(it);
+ return true;
+ }
+ return false;
}
RpcConnection::ExclusiveSocket::ExclusiveSocket(const sp<RpcConnection>& connection, SocketUse use)
@@ -335,37 +350,31 @@
// 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);
+ // A server/looper should always use a dedicated connection if available
+ 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();
- }
+ // 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)
+ // USE SERVING SOCKET (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 */);
+ // server sockets are always assigned to a thread
+ findSocket(tid, &exclusive, nullptr /*available*/, mConnection->mServers,
+ 0 /* index hint */);
}
// if our thread is already using a connection, prioritize using that
@@ -379,8 +388,6 @@
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 "