libbinder_ndk: _disableBackgroundScheduling

ABinderProcess_disableBackgroundScheduling

In preparation for adding it to #systemapi/#llndk once we can
change APIs again.

Bug: 389143775
Test: N/A
Change-Id: I5f7dd806f7664487f07f4c3b695e8456513083a9

Author: Steven Moreland

libs/binder/ndk/include_platform/android/binder_ibinder_platform.h

@@ -62,6 +62,8 @@ __attribute__((weak, warn_unused_result)) const char* AIBinder_getCallingSid() _
  * This must be called before the object is sent to another process.
  * Aborts on invalid values. Not thread safe.
  *
+ * This overrides the setting in ABinderProcess_disableBackgroundScheduling.
+ *
  * \param binder local server binder to set the policy for
  * \param policy scheduler policy as defined in linux UAPI
  * \param priority priority. [-20..19] for SCHED_NORMAL, [1..99] for RT

libs/binder/ndk/include_platform/android/binder_process.h

@@ -74,6 +74,19 @@ bool ABinderProcess_isThreadPoolStarted(void);
  */
 void ABinderProcess_joinThreadPool(void);
 
+/**
+ * Disables (or enables) background scheduling.
+ *
+ * By default, binder threads execute at a lower priority. However, this can cause
+ * priority inversion, so it is recommended to be disabled in high priority
+ * or in system processes.
+ *
+ * See also AIBinder_setMinSchedulerPolicy, which overrides this setting.
+ *
+ * \param disable whether to disable background scheduling
+ */
+void ABinderProcess_disableBackgroundScheduling(bool disable);
+
 /**
  * This gives you an fd to wait on. Whenever data is available on the fd,
  * ABinderProcess_handlePolledCommands can be called to handle binder queries.

libs/binder/ndk/libbinder_ndk.map.txt

@@ -229,6 +229,7 @@ LIBBINDER_NDK_PLATFORM {
         AIBinder_fromPlatformBinder*;
         AIBinder_toPlatformBinder*;
         AParcel_viewPlatformParcel*;
+        ABinderProcess_disableBackgroundScheduling;
     };
   local:
     *;

libs/binder/ndk/process.cpp

@@ -36,6 +36,10 @@ void ABinderProcess_joinThreadPool(void) {
     IPCThreadState::self()->joinThreadPool();
 }
 
+void ABinderProcess_disableBackgroundScheduling(bool disable) {
+    IPCThreadState::disableBackgroundScheduling(disable);
+}
+
 binder_status_t ABinderProcess_setupPolling(int* fd) {
     return IPCThreadState::self()->setupPolling(fd);
 }