Merge lp:~vanvugt/mir/fix-1373809 into lp:mir

[Daniel van Vugt]

Avoid polling in a loop with timeout zero most of the time. That
will only waste CPU. (LP: #1373809)

This also fixes test failure LP: #1373826.

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review: Approve (continuous-integration)

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PASSED: Continuous integration, rev:1938
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review: Approve (continuous-integration)

[Alexandros Frantzis (afrantzis)]

Looks sensible.

Does it make sense to experiment with other timeout values, in order to find an even better trade-off between CPU consumption and event latency?

review: Approve

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PASSED: Continuous integration, rev:1938
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review: Approve (continuous-integration)

[Kevin DuBois (kdub)]

looks good to me

review: Approve

=== modified file 'src/common/input/android/android_input_receiver.cpp'
--- src/common/input/android/android_input_receiver.cpp	2014-09-25 07:57:28 +0000
+++ src/common/input/android/android_input_receiver.cpp	2014-09-25 09:02:15 +0000
@@ -142,11 +142,19 @@
     }
 
     auto reduced_timeout = timeout;
-    if (input_consumer->hasDeferredEvent() || input_consumer->hasPendingBatch())
+    if (input_consumer->hasDeferredEvent())
     {
         // consume() didn't finish last time. Retry it immediately.
         reduced_timeout = std::chrono::milliseconds::zero();
     }
+    else if (input_consumer->hasPendingBatch())
+    {
+        // When in constant motion we will usually "hasPendingBatch".
+        // But the batch won't get flushed until the next frame interval,
+        // so be sure to use a non-zero sleep time to avoid spinning the CPU
+        // for the whole interval...
+        reduced_timeout = std::chrono::milliseconds(1);
+    }
 
     auto result = looper->pollOnce(reduced_timeout.count());
     if (result == ALOOPER_POLL_WAKE)

=== modified file 'tests/unit-tests/client/input/test_android_input_receiver.cpp'
--- tests/unit-tests/client/input/test_android_input_receiver.cpp	2014-09-25 07:57:28 +0000
+++ tests/unit-tests/client/input/test_android_input_receiver.cpp	2014-09-25 09:02:15 +0000
@@ -243,8 +243,11 @@
     // Sadly using real time as droidinput::Looper doesn't use a mocked clock.
     ASSERT_LT(duration_cast<nanoseconds>(duration).count(), one_frame);
 
+    // Verify we don't use all the CPU by not sleeping (LP: #1373809)
+    EXPECT_GT(duration_cast<nanoseconds>(duration).count(), one_millisecond);
+
     // But later in a frame or so, the motion will be reported:
-    t += one_frame;
+    t += 2 * one_frame;  // Account for the new slower 55Hz event rate
     ASSERT_TRUE(receiver.next_event(max_timeout, ev));
     ASSERT_EQ(mir_event_type_motion, ev.type);
 }