Rewrite get_sched_policy_name for safety.

This way you'll get a build time error if you make the usual mistake of
adding to the enum but not adding an entry to the array.

Also improve the unit tests, and fix get_sched_policy_name's incorrect
behavior on invalid inputs.

Bug: N/A
Test: ran tests
Change-Id: Iefcb1ec9ef66267837da7a576c8be3d0cfb16cd0

3 files changed, 20 insertions, 18 deletions

diff --git a/libcutils/Android.bp b/libcutils/Android.bp
index 6d00dc6ee..dd46750fc 100644
--- a/libcutils/Android.bp
+++ b/libcutils/Android.bp
@@ -164,6 +164,7 @@ cc_library {
 
     shared_libs: ["liblog"],
     header_libs: [
+        "libbase_headers",
         "libcutils_headers",
         "libutils_headers",
     ],
diff --git a/libcutils/sched_policy.cpp b/libcutils/sched_policy.cpp
index f72ec52d6..3fa548f78 100644
--- a/libcutils/sched_policy.cpp
+++ b/libcutils/sched_policy.cpp
@@ -25,6 +25,7 @@
 #include <string.h>
 #include <unistd.h>
 
+#include <android-base/macros.h>
 #include <log/log.h>
 
 /* Re-map SP_DEFAULT to the system default policy, and leave other values unchanged.
@@ -460,16 +461,16 @@ int get_sched_policy(int /*tid*/, SchedPolicy* policy) {
 
 #endif
 
-const char *get_sched_policy_name(SchedPolicy policy)
-{
+const char* get_sched_policy_name(SchedPolicy policy) {
     policy = _policy(policy);
-    static const char* const strings[SP_CNT] = {
+    static const char* const kSchedPolicyNames[] = {
             [SP_BACKGROUND] = "bg", [SP_FOREGROUND] = "fg", [SP_SYSTEM] = "  ",
             [SP_AUDIO_APP] = "aa",  [SP_AUDIO_SYS] = "as",  [SP_TOP_APP] = "ta",
             [SP_RT_APP] = "rt",     [SP_RESTRICTED] = "rs",
     };
-    if ((policy < SP_CNT) && (strings[policy] != NULL))
-        return strings[policy];
-    else
+    static_assert(arraysize(kSchedPolicyNames) == SP_CNT, "missing name");
+    if (policy < SP_BACKGROUND || policy >= SP_CNT) {
         return "error";
+    }
+    return kSchedPolicyNames[policy];
 }
diff --git a/libcutils/tests/sched_policy_test.cpp b/libcutils/tests/sched_policy_test.cpp
index 173174a1a..5942ee5b6 100644
--- a/libcutils/tests/sched_policy_test.cpp
+++ b/libcutils/tests/sched_policy_test.cpp
@@ -60,6 +60,12 @@ long long medianSleepTime() {
     return sleepTimes[median];
 }
 
+static void AssertPolicy(SchedPolicy expected_policy) {
+    SchedPolicy current_policy;
+    ASSERT_EQ(0, get_sched_policy(0, &current_policy));
+    EXPECT_EQ(expected_policy, current_policy);
+}
+
 TEST(SchedPolicy, set_sched_policy) {
     if (!hasCapSysNice()) {
         GTEST_LOG_(INFO) << "skipping test that requires CAP_SYS_NICE";
@@ -76,23 +82,17 @@ TEST(SchedPolicy, set_sched_policy) {
     const unsigned int BG_FG_SLACK_FACTOR = 100;
 
     ASSERT_EQ(0, set_sched_policy(0, SP_BACKGROUND));
+    AssertPolicy(SP_BACKGROUND);
     auto bgSleepTime = medianSleepTime();
 
     ASSERT_EQ(0, set_sched_policy(0, SP_FOREGROUND));
+    AssertPolicy(SP_FOREGROUND);
     auto fgSleepTime = medianSleepTime();
     ASSERT_GT(bgSleepTime, fgSleepTime * BG_FG_SLACK_FACTOR);
 }
 
-TEST(SchedPolicy, get_sched_policy) {
-    SchedPolicy policy;
-    ASSERT_EQ(0, get_sched_policy(0, &policy));
-
-    const char *policyName = get_sched_policy_name(policy);
-    EXPECT_NE(nullptr, policyName);
-    EXPECT_STRNE("error", policyName);
-
-    ASSERT_EQ(0, set_sched_policy(0, SP_BACKGROUND));
-    SchedPolicy newPolicy;
-    ASSERT_EQ(0, get_sched_policy(0, &newPolicy));
-    EXPECT_EQ(SP_BACKGROUND, newPolicy);
+TEST(SchedPolicy, get_sched_policy_name) {
+    EXPECT_STREQ("bg", get_sched_policy_name(SP_BACKGROUND));
+    EXPECT_STREQ("error", get_sched_policy_name(SchedPolicy(-2)));
+    EXPECT_STREQ("error", get_sched_policy_name(SP_CNT));
 }