commit 620d2dc61a124a69020949daa98164908b728e0c
author Jon Spivack <spivack@google.com> Fri Mar 06 13:58:01 2020 -0800
committer Jon Spivack <spivack@google.com> Tue Mar 10 16:56:46 2020 -0700
tree 09125e2118b49b145547054a4eacd5962ce50866
parent 70f592a6cf9a63cdf1b01274a4430b2de1505af9

LazyServiceRegistrar: Add flag to prevent shutdown

This flag can be used to temporarily prevent dynamic services from being killed. For example, if a service needs to perform a task in the background it can set this flag and then disable it once the task is complete. The service will then go back to standard lazy behavior.

Bug: 150967269
Test: aidl_lazy_test
Change-Id: I840bbe4b6b0406f0e4de610367290448e7edd3de

cmds/servicemanager/ServiceManager.cpp

diff --git a/cmds/servicemanager/ServiceManager.cpp b/cmds/servicemanager/ServiceManager.cpp
index abe6436..1e88aaf 100644
--- a/cmds/servicemanager/ServiceManager.cpp
+++ b/cmds/servicemanager/ServiceManager.cpp
@@ -532,6 +532,8 @@
     if (clients < 0 || clients > 2) {
         // client callbacks are either disabled or there are other clients
         LOG(INFO) << "Tried to unregister " << name << ", but there are clients: " << clients;
+        // Set this flag to ensure the clients are acknowledged in the next callback
+        serviceIt->second.guaranteeClient = true;
         return Status::fromExceptionCode(Status::EX_ILLEGAL_STATE);
     }
 

libs/binder/LazyServiceRegistrar.cpp

diff --git a/libs/binder/LazyServiceRegistrar.cpp b/libs/binder/LazyServiceRegistrar.cpp
index 71d8130..74aece8 100644
--- a/libs/binder/LazyServiceRegistrar.cpp
+++ b/libs/binder/LazyServiceRegistrar.cpp
@@ -31,11 +31,16 @@
 
 class ClientCounterCallback : public ::android::os::BnClientCallback {
 public:
-    ClientCounterCallback() : mNumConnectedServices(0) {}
+    ClientCounterCallback() : mNumConnectedServices(0), mForcePersist(false) {}
 
     bool registerService(const sp<IBinder>& service, const std::string& name,
                          bool allowIsolated, int dumpFlags);
 
+    /**
+     * Set a flag to prevent services from automatically shutting down
+     */
+    void forcePersist(bool persist);
+
 protected:
     Status onClients(const sp<IBinder>& service, bool clients) override;
 
@@ -60,6 +65,8 @@
      * Map of registered names and services
      */
     std::map<std::string, Service> mRegisteredServices;
+
+    bool mForcePersist;
 };
 
 bool ClientCounterCallback::registerService(const sp<IBinder>& service, const std::string& name,
@@ -88,6 +95,14 @@
     return true;
 }
 
+void ClientCounterCallback::forcePersist(bool persist) {
+    mForcePersist = persist;
+    if(!mForcePersist) {
+        // Attempt a shutdown in case the number of clients hit 0 while the flag was on
+        tryShutdown();
+    }
+}
+
 /**
  * onClients is oneway, so no need to worry about multi-threading. Note that this means multiple
  * invocations could occur on different threads however.
@@ -103,14 +118,21 @@
           mNumConnectedServices, mRegisteredServices.size(),
           String8(service->getInterfaceDescriptor()).string(), clients);
 
-    if (mNumConnectedServices == 0) {
-        tryShutdown();
-    }
-
+    tryShutdown();
     return Status::ok();
 }
 
 void ClientCounterCallback::tryShutdown() {
+    if(mNumConnectedServices > 0) {
+        // Should only shut down if there are no clients
+        return;
+    }
+
+    if(mForcePersist) {
+        ALOGI("Shutdown prevented by forcePersist override flag.");
+        return;
+    }
+
     ALOGI("Trying to shut down the service. No clients in use for any service in process.");
 
     auto manager = interface_cast<AidlServiceManager>(asBinder(defaultServiceManager()));
@@ -165,5 +187,9 @@
     return OK;
 }
 
+void LazyServiceRegistrar::forcePersist(bool persist) {
+    mClientCC->forcePersist(persist);
+}
+
 }  // namespace hardware
 }  // namespace android
\ No newline at end of file

libs/binder/include/binder/LazyServiceRegistrar.h

diff --git a/libs/binder/include/binder/LazyServiceRegistrar.h b/libs/binder/include/binder/LazyServiceRegistrar.h
index efdecc4..6d711bc 100644
--- a/libs/binder/include/binder/LazyServiceRegistrar.h
+++ b/libs/binder/include/binder/LazyServiceRegistrar.h
@@ -34,6 +34,12 @@
                               const std::string& name = "default",
                               bool allowIsolated = false,
                               int dumpFlags = IServiceManager::DUMP_FLAG_PRIORITY_DEFAULT);
+     /**
+      * Force the service to persist, even when it has 0 clients.
+      * If setting this flag from the server side, make sure to do so before calling registerService,
+      * or there may be a race with the default dynamic shutdown.
+      */
+     void forcePersist(bool persist);
 
    private:
      std::shared_ptr<internal::ClientCounterCallback> mClientCC;