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Commit 9ba7c1c1 authored by destradaa's avatar destradaa
Browse files

Intern strings used in Sensor information. 

By creating a local 'interning map', Sensor information, such as: name, vendor,
stringType, and requirePermissions; 92 string objects are not needed anymore.
This frees ~6KB of memory in all processes accessing SensorManager.

Change-Id: Idfdc98160363bec844c34fc3b71f5e8d7843a7be
parent 4a39e1bb

core/java/android/hardware/Sensor.java

+92 −0
Original line number Diff line number Diff line
@@ -810,4 +810,96 @@ public final class Sensor { 
                + ", type=" + mType + ", maxRange=" + mMaxRange + ", resolution=" + mResolution

                + ", power=" + mPower + ", minDelay=" + mMinDelay + "}";

    }



    /**

     * Sets the Type associated with the sensor.

     * NOTE: to be used only by native bindings in SensorManager.

     *

     * This allows interned static strings to be used across all representations of the Sensor. If

     * a sensor type is not referenced here, it will still be interned by the native SensorManager.

     *

     * @return {@code true} if the StringType was successfully set, {@code false} otherwise.

     */

    private boolean setType(int value) {

        mType = value;

        switch (mType) {

            case TYPE_ACCELEROMETER:

                mStringType = STRING_TYPE_ACCELEROMETER;

                return true;

            case TYPE_AMBIENT_TEMPERATURE:

                mStringType = STRING_TYPE_AMBIENT_TEMPERATURE;

                return true;

            case TYPE_GAME_ROTATION_VECTOR:

                mStringType = STRING_TYPE_GAME_ROTATION_VECTOR;

                return true;

            case TYPE_GEOMAGNETIC_ROTATION_VECTOR:

                mStringType = STRING_TYPE_GEOMAGNETIC_ROTATION_VECTOR;

                return true;

            case TYPE_GLANCE_GESTURE:

                mStringType = STRING_TYPE_GLANCE_GESTURE;

                return true;

            case TYPE_GRAVITY:

                mStringType = STRING_TYPE_GRAVITY;

                return true;

            case TYPE_GYROSCOPE:

                mStringType = STRING_TYPE_GYROSCOPE;

                return true;

            case TYPE_GYROSCOPE_UNCALIBRATED:

                mStringType = STRING_TYPE_GYROSCOPE_UNCALIBRATED;

                return true;

            case TYPE_HEART_RATE:

                mStringType = STRING_TYPE_HEART_RATE;

                return true;

            case TYPE_LIGHT:

                mStringType = STRING_TYPE_LIGHT;

                return true;

            case TYPE_LINEAR_ACCELERATION:

                mStringType = STRING_TYPE_LINEAR_ACCELERATION;

                return true;

            case TYPE_MAGNETIC_FIELD:

                mStringType = STRING_TYPE_MAGNETIC_FIELD;

                return true;

            case TYPE_MAGNETIC_FIELD_UNCALIBRATED:

                mStringType = STRING_TYPE_MAGNETIC_FIELD_UNCALIBRATED;

                return true;

            case TYPE_PICK_UP_GESTURE:

                mStringType = STRING_TYPE_PICK_UP_GESTURE;

                return true;

            case TYPE_PRESSURE:

                mStringType = STRING_TYPE_PRESSURE;

                return true;

            case TYPE_PROXIMITY:

                mStringType = STRING_TYPE_PROXIMITY;

                return true;

            case TYPE_RELATIVE_HUMIDITY:

                mStringType = STRING_TYPE_RELATIVE_HUMIDITY;

                return true;

            case TYPE_ROTATION_VECTOR:

                mStringType = STRING_TYPE_ROTATION_VECTOR;

                return true;

            case TYPE_SIGNIFICANT_MOTION:

                mStringType = STRING_TYPE_SIGNIFICANT_MOTION;

                return true;

            case TYPE_STEP_COUNTER:

                mStringType = STRING_TYPE_STEP_COUNTER;

                return true;

            case TYPE_STEP_DETECTOR:

                mStringType = STRING_TYPE_STEP_DETECTOR;

                return true;

            case TYPE_TILT_DETECTOR:

                mStringType = SENSOR_STRING_TYPE_TILT_DETECTOR;

                return true;

            case TYPE_WAKE_GESTURE:

                mStringType = STRING_TYPE_WAKE_GESTURE;

                return true;

            case TYPE_ORIENTATION:

                mStringType = STRING_TYPE_ORIENTATION;

                return true;

            case TYPE_TEMPERATURE:

                mStringType = STRING_TYPE_TEMPERATURE;

                return true;

            default:

                return false;

        }

    }

}

core/jni/android_hardware_SensorManager.cpp

+53 −9
Original line number Diff line number Diff line
@@ -16,6 +16,8 @@ 


#define LOG_TAG "SensorManager"



#include <map>



#include <utils/Log.h>

#include <utils/Looper.h>
@@ -44,7 +46,6 @@ struct SensorOffsets 
    jfieldID    vendor;

    jfieldID    version;

    jfieldID    handle;

    jfieldID    type;

    jfieldID    range;

    jfieldID    resolution;

    jfieldID    power;
@@ -55,6 +56,7 @@ struct SensorOffsets 
    jfieldID    requiredPermission;

    jfieldID    maxDelay;

    jfieldID    flags;

    jmethodID   setType;

} gSensorOffsets;
@@ -71,7 +73,6 @@ nativeClassInit (JNIEnv *_env, jclass _this) 
    sensorOffsets.vendor      = _env->GetFieldID(sensorClass, "mVendor",    "Ljava/lang/String;");

    sensorOffsets.version     = _env->GetFieldID(sensorClass, "mVersion",   "I");

    sensorOffsets.handle      = _env->GetFieldID(sensorClass, "mHandle",    "I");

    sensorOffsets.type        = _env->GetFieldID(sensorClass, "mType",      "I");

    sensorOffsets.range       = _env->GetFieldID(sensorClass, "mMaxRange",  "F");

    sensorOffsets.resolution  = _env->GetFieldID(sensorClass, "mResolution","F");

    sensorOffsets.power       = _env->GetFieldID(sensorClass, "mPower",     "F");
@@ -84,6 +85,47 @@ nativeClassInit (JNIEnv *_env, jclass _this) 
                                                        "Ljava/lang/String;");

    sensorOffsets.maxDelay    = _env->GetFieldID(sensorClass, "mMaxDelay",  "I");

    sensorOffsets.flags = _env->GetFieldID(sensorClass, "mFlags",  "I");

    sensorOffsets.setType = _env->GetMethodID(sensorClass, "setType", "(I)Z");

}



/**

 * A key comparator predicate.

 * It is used to intern strings associated with Sensor data.

 * It defines a 'Strict weak ordering' for the interned strings.

 */

class InternedStringCompare {

public:

    bool operator()(const String8* string1, const String8* string2) const {

        if (string1 == NULL) {

            return string2 != NULL;

        }

        return string1->compare(*string2) < 0;

    }

};



/**

 * A localized interning mechanism for Sensor strings.

 * We implement our own interning to avoid the overhead of using java.lang.String#intern().

 * It is common that Vendor, StringType, and RequirePermission data is common between many of the

 * Sensors, by interning the memory usage to represent Sensors is optimized.

 */

static jstring

getInternedString(JNIEnv *env, const String8* string) {

    static std::map<const String8*, jstring, InternedStringCompare> internedStrings;



    jstring internedString;

    std::map<const String8*, jstring>::iterator iterator = internedStrings.find(string);

    if (iterator != internedStrings.end()) {

        internedString = iterator->second;

    } else {

        jstring localString = env->NewStringUTF(string->string());

        // we are implementing our own interning so expect these strings to be backed by global refs

        internedString = (jstring) env->NewGlobalRef(localString);

        internedStrings.insert(std::make_pair(string, internedString));

        env->DeleteLocalRef(localString);

    }



    return internedString;

}



static jint
@@ -93,20 +135,19 @@ nativeGetNextSensor(JNIEnv *env, jclass clazz, jobject sensor, jint next) 


    Sensor const* const* sensorList;

    size_t count = mgr.getSensorList(&sensorList);

    if (size_t(next) >= count)

    if (size_t(next) >= count) {

        return -1;

    }



    Sensor const* const list = sensorList[next];

    const SensorOffsets& sensorOffsets(gSensorOffsets);

    jstring name = env->NewStringUTF(list->getName().string());

    jstring vendor = env->NewStringUTF(list->getVendor().string());

    jstring stringType = env->NewStringUTF(list->getStringType().string());

    jstring requiredPermission = env->NewStringUTF(list->getRequiredPermission().string());

    jstring name = getInternedString(env, &list->getName());

    jstring vendor = getInternedString(env, &list->getVendor());

    jstring requiredPermission = getInternedString(env, &list->getRequiredPermission());

    env->SetObjectField(sensor, sensorOffsets.name,      name);

    env->SetObjectField(sensor, sensorOffsets.vendor,    vendor);

    env->SetIntField(sensor, sensorOffsets.version,      list->getVersion());

    env->SetIntField(sensor, sensorOffsets.handle,       list->getHandle());

    env->SetIntField(sensor, sensorOffsets.type,         list->getType());

    env->SetFloatField(sensor, sensorOffsets.range,      list->getMaxValue());

    env->SetFloatField(sensor, sensorOffsets.resolution, list->getResolution());

    env->SetFloatField(sensor, sensorOffsets.power,      list->getPowerUsage());
@@ -115,11 +156,14 @@ nativeGetNextSensor(JNIEnv *env, jclass clazz, jobject sensor, jint next) 
                     list->getFifoReservedEventCount());

    env->SetIntField(sensor, sensorOffsets.fifoMaxEventCount,

                     list->getFifoMaxEventCount());

    env->SetObjectField(sensor, sensorOffsets.stringType, stringType);

    env->SetObjectField(sensor, sensorOffsets.requiredPermission,

                        requiredPermission);

    env->SetIntField(sensor, sensorOffsets.maxDelay, list->getMaxDelay());

    env->SetIntField(sensor, sensorOffsets.flags, list->getFlags());

    if (env->CallBooleanMethod(sensor, sensorOffsets.setType, list->getType()) == JNI_FALSE) {

        jstring stringType = getInternedString(env, &list->getStringType());

        env->SetObjectField(sensor, sensorOffsets.stringType, stringType);

    }

    next++;

    return size_t(next) < count ? next : 0;

}