Scheduling group cleanup - add comment, SP_DEFAULT

Also tid == 0 maps to gettid() on platforms that support it.
This is needed by mediaserver code that was formerly using
the old C++ API.

Change-Id: I8baaa3e42315c9b924cec26b6da01e7cb69e0078

2 files changed, 26 insertions, 0 deletions

diff --git a/include/cutils/sched_policy.h b/include/cutils/sched_policy.h
index 753a08c..c6e4fc4 100644
--- a/include/cutils/sched_policy.h
+++ b/include/cutils/sched_policy.h
@@ -21,21 +21,26 @@
 extern "C" {
 #endif
 
+/* Keep in sync with THREAD_GROUP_* in frameworks/base/core/java/android/os/Process.java */
 typedef enum {
+    SP_DEFAULT    = -1,
     SP_BACKGROUND = 0,
     SP_FOREGROUND = 1,
     SP_CNT,
     SP_MAX        = SP_CNT - 1,
+    SP_SYSTEM_DEFAULT = SP_FOREGROUND,
 } SchedPolicy;
 
 /* Assign thread tid to the cgroup associated with the specified policy.
  * If the thread is a thread group leader, that is it's gettid() == getpid(),
  * then the other threads in the same thread group are _not_ affected.
+ * On platforms which support gettid(), zero tid means current thread.
  * Return value: 0 for success, or -errno for error.
  */
 extern int set_sched_policy(int tid, SchedPolicy policy);
 
 /* Return the policy associated with the cgroup of thread tid via policy pointer.
+ * On platforms which support gettid(), zero tid means current thread.
  * Return value: 0 for success, or -1 for error and set errno.
  */
 extern int get_sched_policy(int tid, SchedPolicy *policy);
diff --git a/libcutils/sched_policy.c b/libcutils/sched_policy.c
index 35d362a..345532b 100644
--- a/libcutils/sched_policy.c
+++ b/libcutils/sched_policy.c
@@ -189,6 +189,11 @@ static int getSchedulerGroup(int tid, char* buf, size_t bufLen)
 
 int get_sched_policy(int tid, SchedPolicy *policy)
 {
+#ifdef HAVE_GETTID
+    if (tid == 0) {
+        tid = gettid();
+    }
+#endif
     pthread_once(&the_once, __initialize);
 
     if (__sys_supports_schedgroups) {
@@ -219,8 +224,23 @@ int get_sched_policy(int tid, SchedPolicy *policy)
     return 0;
 }
 
+/* Re-map SP_DEFAULT to the system default policy, and leave other values unchanged.
+ * Call this any place a SchedPolicy is used as an input parameter.
+ * Returns the possibly re-mapped policy.
+ */
+static inline SchedPolicy _policy(SchedPolicy p)
+{
+   return p == SP_DEFAULT ? SP_SYSTEM_DEFAULT : p;
+}
+
 int set_sched_policy(int tid, SchedPolicy policy)
 {
+#ifdef HAVE_GETTID
+    if (tid == 0) {
+        tid = gettid();
+    }
+#endif
+    policy = _policy(policy);
     pthread_once(&the_once, __initialize);
 
 #if POLICY_DEBUG
@@ -275,6 +295,7 @@ int set_sched_policy(int tid, SchedPolicy policy)
 
 const char *get_sched_policy_name(SchedPolicy policy)
 {
+    policy = _policy(policy);
     static const char * const strings[SP_CNT] = {
        [SP_BACKGROUND] = "bg",
        [SP_FOREGROUND] = "fg",