libbinder: more forcePersist docs

Documenting recommending use for now. Looked at adding a shared library
destructor, but this has limited use when people use _exit, when persist
HALs sometimes exit manually early, and since it only corresponds to
this one mechanism. Given perf team work targetting understanding memory
uses/process which are starting, we can focus/rely on more general
infrastructure.

Fixes: 187946888
Test: N/A
Change-Id: I67c2477bccd9ebc789e20527d5692ea3a107c675

2 files changed, 10 insertions, 2 deletions

diff --git a/libs/binder/include/binder/LazyServiceRegistrar.h b/libs/binder/include/binder/LazyServiceRegistrar.h
index 96597320f6..f3ba830923 100644
--- a/libs/binder/include/binder/LazyServiceRegistrar.h
+++ b/libs/binder/include/binder/LazyServiceRegistrar.h
@@ -50,8 +50,12 @@ class LazyServiceRegistrar {
                               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.
+      * 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.
+      *
+      * This should only be used if it is every eventually set to false. If a
+      * service needs to persist but doesn't need to dynamically shut down,
+      * prefer to control it with another mechanism such as ctl.start.
       */
      void forcePersist(bool persist);
 
diff --git a/libs/binder/ndk/include_platform/android/binder_manager.h b/libs/binder/ndk/include_platform/android/binder_manager.h
index a90b4aabca..db72067e33 100644
--- a/libs/binder/ndk/include_platform/android/binder_manager.h
+++ b/libs/binder/ndk/include_platform/android/binder_manager.h
@@ -135,6 +135,10 @@ bool AServiceManager_isUpdatableViaApex(const char* instance) __INTRODUCED_IN(31
 /**
  * Prevent lazy services without client from shutting down their process
  *
+ * This should only be used if it is every eventually set to false. If a
+ * service needs to persist but doesn't need to dynamically shut down,
+ * prefer to control it with another mechanism.
+ *
  * \param persist 'true' if the process should not exit.
  */
 void AServiceManager_forceLazyServicesPersist(bool persist) __INTRODUCED_IN(31);