[REFACTOR] health 2.0: healthd_common -> libhealthloop

This change converts the original healthd_common.cpp to a
C++ class, HealthLoop, that manages the infinite loop in health-related
modules (charger, health HAL, healthd, etc.). By doing so, the global
static variables (including FDs and healthd_mode_ops) are cleaned up.

This helps us implement health HAL 2.1.

In order to support legacy modules (namely, healthd, charger, health HAL
2.0, which all depends on android.hardware.health@2.0-impl), a
healthd_common_adapter.cpp file is added to
android.hardware.health@2.0-impl, so that the following functions
in healthd/healthd.h continues to be implemented using the global
healthd_mode_ops:
    - healthd_register_event
    - healthd_battery_update_internal

Test: boot up the device and run VTS test on health HAL.
Bug: 137670450
Bug: 142260281
Change-Id: Iadcfc1315155404a3600f0e1219b5bc370d96409
diff --git a/health/2.0/default/Android.bp b/health/2.0/default/Android.bp
index a85a704..ead560b 100644
--- a/health/2.0/default/Android.bp
+++ b/health/2.0/default/Android.bp
@@ -33,7 +33,11 @@
     vendor_available: true,
     srcs: [
         "Health.cpp",
-        "healthd_common.cpp",
+        "healthd_common_adapter.cpp",
+    ],
+
+    whole_static_libs: [
+        "libhealthloop",
     ],
 
     export_include_dirs: ["include"],
diff --git a/health/2.0/default/healthd_common_adapter.cpp b/health/2.0/default/healthd_common_adapter.cpp
new file mode 100644
index 0000000..8fc689d
--- /dev/null
+++ b/health/2.0/default/healthd_common_adapter.cpp
@@ -0,0 +1,74 @@
+/*
+ * Copyright (C) 2019 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+// Support legacy functions in healthd/healthd.h using healthd_mode_ops.
+// New code should use HealthLoop directly instead.
+
+#include <memory>
+
+#include <cutils/klog.h>
+#include <health/HealthLoop.h>
+#include <health2/Health.h>
+#include <healthd/healthd.h>
+
+using android::hardware::health::HealthLoop;
+using android::hardware::health::V2_0::implementation::Health;
+
+struct healthd_mode_ops* healthd_mode_ops = nullptr;
+
+// Adapter of HealthLoop to use legacy healthd_mode_ops.
+class HealthLoopAdapter : public HealthLoop {
+   public:
+    // Expose internal functions, assuming clients calls them in the same thread
+    // where StartLoop is called.
+    int RegisterEvent(int fd, BoundFunction func, EventWakeup wakeup) {
+        return HealthLoop::RegisterEvent(fd, func, wakeup);
+    }
+    void AdjustWakealarmPeriods(bool charger_online) {
+        return HealthLoop::AdjustWakealarmPeriods(charger_online);
+    }
+   protected:
+    void Init(healthd_config* config) override { healthd_mode_ops->init(config); }
+    void Heartbeat() override { healthd_mode_ops->heartbeat(); }
+    int PrepareToWait() override { return healthd_mode_ops->preparetowait(); }
+    void ScheduleBatteryUpdate() override { Health::getImplementation()->update(); }
+};
+static std::unique_ptr<HealthLoopAdapter> health_loop;
+
+int healthd_register_event(int fd, void (*handler)(uint32_t), EventWakeup wakeup) {
+    auto wrapped_handler = [handler](auto*, uint32_t epevents) { handler(epevents); };
+    return health_loop->RegisterEvent(fd, wrapped_handler, wakeup);
+}
+
+void healthd_battery_update_internal(bool charger_online) {
+    health_loop->AdjustWakealarmPeriods(charger_online);
+}
+
+int healthd_main() {
+    if (!healthd_mode_ops) {
+        KLOG_ERROR("healthd ops not set, exiting\n");
+        exit(1);
+    }
+
+    health_loop = std::make_unique<HealthLoopAdapter>();
+
+    int ret = health_loop->StartLoop();
+
+    // Should not reach here. The following will exit().
+    health_loop.reset();
+
+    return ret;
+}