diff --git a/libs/binder/RpcServer.cpp b/libs/binder/RpcServer.cpp
index 9a0be92..8f2805f 100644
--- a/libs/binder/RpcServer.cpp
+++ b/libs/binder/RpcServer.cpp
@@ -19,6 +19,7 @@
 #include <sys/socket.h>
 #include <sys/un.h>
 
+#include <thread>
 #include <vector>
 
 #include <binder/Parcel.h>
@@ -41,16 +42,19 @@
     mAgreedExperimental = true;
 }
 
-sp<RpcConnection> RpcServer::addClientConnection() {
-    LOG_ALWAYS_FATAL_IF(!mAgreedExperimental, "no!");
-
-    auto connection = RpcConnection::make();
-    connection->setForServer(sp<RpcServer>::fromExisting(this));
+void RpcServer::setMaxThreads(size_t threads) {
+    LOG_ALWAYS_FATAL_IF(threads <= 0, "RpcServer is useless without threads");
     {
+        // this lock should only ever be needed in the error case
         std::lock_guard<std::mutex> _l(mLock);
-        mConnections.push_back(connection);
+        LOG_ALWAYS_FATAL_IF(mConnections.size() > 0,
+                            "Must specify max threads before creating a connection");
     }
-    return connection;
+    mMaxThreads = threads;
+}
+
+size_t RpcServer::getMaxThreads() {
+    return mMaxThreads;
 }
 
 void RpcServer::setRootObject(const sp<IBinder>& binder) {
@@ -63,4 +67,35 @@
     return mRootObject;
 }
 
+sp<RpcConnection> RpcServer::addClientConnection() {
+    LOG_ALWAYS_FATAL_IF(!mAgreedExperimental, "no!");
+
+    auto connection = RpcConnection::make();
+    connection->setForServer(sp<RpcServer>::fromExisting(this));
+    {
+        std::lock_guard<std::mutex> _l(mLock);
+        LOG_ALWAYS_FATAL_IF(mStarted,
+                            "currently only supports adding client connections at creation time");
+        mConnections.push_back(connection);
+    }
+    return connection;
+}
+
+void RpcServer::join() {
+    std::vector<std::thread> pool;
+    {
+        std::lock_guard<std::mutex> _l(mLock);
+        mStarted = true;
+        for (const sp<RpcConnection>& connection : mConnections) {
+            for (size_t i = 0; i < mMaxThreads; i++) {
+                pool.push_back(std::thread([=] { connection->join(); }));
+            }
+        }
+    }
+
+    // TODO(b/185167543): don't waste extra thread for join, and combine threads
+    // between clients
+    for (auto& t : pool) t.join();
+}
+
 } // namespace android