/*
* Copyright (C) 2009 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.
*/
package com.android.common;
import android.content.SharedPreferences;
import android.net.http.AndroidHttpClient;
import android.text.format.Time;
import java.util.Map;
import java.util.TreeMap;
/**
* Tracks the success/failure history of a particular network operation in
* persistent storage and computes retry strategy accordingly. Handles
* exponential backoff, periodic rescheduling, event-driven triggering,
* retry-after moratorium intervals, etc. based on caller-specified parameters.
*
* <p>This class does not directly perform or invoke any operations,
* it only keeps track of the schedule. Somebody else needs to call
* {@link #getNextTimeMillis} as appropriate and do the actual work.
*/
public class OperationScheduler {
/** Tunable parameter options for {@link #getNextTimeMillis}. */
public static class Options {
/** Wait this long after every error before retrying. */
public long backoffFixedMillis = 0;
/** Wait this long times the number of consecutive errors so far before retrying. */
public long backoffIncrementalMillis = 5000;
/** Wait this long times 2^(number of consecutive errors so far) before retrying. */
public int backoffExponentialMillis = 0;
/** Maximum duration of moratorium to honor. Mostly an issue for clock rollbacks. */
public long maxMoratoriumMillis = 24 * 3600 * 1000;
/** Minimum duration after success to wait before allowing another trigger. */
public long minTriggerMillis = 0;
/** Automatically trigger this long after the last success. */
public long periodicIntervalMillis = 0;
@Override
public String toString() {
if (backoffExponentialMillis > 0) {
return String.format(
"OperationScheduler.Options[backoff=%.1f+%.1f+%.1f max=%.1f min=%.1f period=%.1f]",
backoffFixedMillis / 1000.0, backoffIncrementalMillis / 1000.0,
backoffExponentialMillis / 1000.0,
maxMoratoriumMillis / 1000.0, minTriggerMillis / 1000.0,
periodicIntervalMillis / 1000.0);
} else {
return String.format(
"OperationScheduler.Options[backoff=%.1f+%.1f max=%.1f min=%.1f period=%.1f]",
backoffFixedMillis / 1000.0, backoffIncrementalMillis / 1000.0,
maxMoratoriumMillis / 1000.0, minTriggerMillis / 1000.0,
periodicIntervalMillis / 1000.0);
}
}
}
private static final String PREFIX = "OperationScheduler_";
private final SharedPreferences mStorage;
/**
* Initialize the scheduler state.
* @param storage to use for recording the state of operations across restarts/reboots
*/
public OperationScheduler(SharedPreferences storage) {
mStorage = storage;
}
/**
* Parse scheduler options supplied in this string form:
*
* <pre>
* backoff=(fixed)+(incremental)[+(exponential)] max=(maxmoratorium) min=(mintrigger) [period=](interval)
* </pre>
*
* All values are times in (possibly fractional) <em>seconds</em> (not milliseconds).
* Omitted settings are left at whatever existing default value was passed in.
*
* <p>
* The default options: <code>backoff=0+5 max=86400 min=0 period=0</code><br>
* Fractions are OK: <code>backoff=+2.5 period=10.0</code><br>
* The "period=" can be omitted: <code>3600</code><br>
*
* @param spec describing some or all scheduler options.
* @param options to update with parsed values.
* @return the options passed in (for convenience)
* @throws IllegalArgumentException if the syntax is invalid
*/
public static Options parseOptions(String spec, Options options)
throws IllegalArgumentException {
for (String param : spec.split(" +")) {
if (param.length() == 0) continue;
if (param.startsWith("backoff=")) {
String[] pieces = param.substring(8).split("\\+");
if (pieces.length > 3) {
throw new IllegalArgumentException("bad value for backoff: [" + spec + "]");
}
if (pieces.length > 0 && pieces[0].length() > 0) {
options.backoffFixedMillis = parseSeconds(pieces[0]);
}
if (pieces.length > 1 && pieces[1].length() > 0) {
options.backoffIncrementalMillis = parseSeconds(pieces[1]);
}
if (pieces.length > 2 && pieces[2].length() > 0) {
options.backoffExponentialMillis = (int)parseSeconds(pieces[2]);
}
} else if (param.startsWith("max=")) {
options.maxMoratoriumMillis = parseSeconds(param.substring(4));
} else if (param.startsWith("min=")) {
options.minTriggerMillis = parseSeconds(param.substring(4));
} else if (param.startsWith("period=")) {
options.periodicIntervalMillis = parseSeconds(param.substring(7));
} else {
options.periodicIntervalMillis = parseSeconds(param);
}
}
return options;
}
private static long parseSeconds(String param) throws NumberFormatException {
return (long) (Float.parseFloat(param) * 1000);
}
/**
* Compute the time of the next operation. Does not modify any state
* (unless the clock rolls backwards, in which case timers are reset).
*
* @param options to use for this computation.
* @return the wall clock time ({@link System#currentTimeMillis()}) when the
* next operation should be attempted -- immediately, if the return value is
* before the current time.
*/
public long getNextTimeMillis(Options options) {
boolean enabledState = mStorage.getBoolean(PREFIX + "enabledState", true);
if (!enabledState) return Long.MAX_VALUE;
boolean permanentError = mStorage.getBoolean(PREFIX + "permanentError", false);
if (permanentError) return Long.MAX_VALUE;
// We do quite a bit of limiting to prevent a clock rollback from totally
// hosing the scheduler. Times which are supposed to be in the past are
// clipped to the current time so we don't languish forever.
int errorCount = mStorage.getInt(PREFIX + "errorCount", 0);
long now = currentTimeMillis();
long lastSuccessTimeMillis = getTimeBefore(PREFIX + "lastSuccessTimeMillis", now);
long lastErrorTimeMillis = getTimeBefore(PREFIX + "lastErrorTimeMillis", now);
long triggerTimeMillis = mStorage.getLong(PREFIX + "triggerTimeMillis", Long.MAX_VALUE);
long moratoriumSetMillis = getTimeBefore(PREFIX + "moratoriumSetTimeMillis", now);
long moratoriumTimeMillis = getTimeBefore(PREFIX + "moratoriumTimeMillis",
moratoriumSetMillis + options.maxMoratoriumMillis);
long time = triggerTimeMillis;
if (options.periodicIntervalMillis > 0) {
time = Math.min(time, lastSuccessTimeMillis + options.periodicIntervalMillis);
}
time = Math.max(time, moratoriumTimeMillis);
time = Math.max(time, lastSuccessTimeMillis + options.minTriggerMillis);
if (errorCount > 0) {
int shift = errorCount-1;
// backoffExponentialMillis is an int, so we can safely
// double it 30 times without overflowing a long.
if (shift > 30) shift = 30;
long backoff = options.backoffFixedMillis +
(options.backoffIncrementalMillis * errorCount) +
(((long)options.backoffExponentialMillis) << shift);
// Treat backoff like a moratorium: don't let the backoff
// time grow too large.
if (moratoriumTimeMillis > 0 && backoff > moratoriumTimeMillis) {
backoff = moratoriumTimeMillis;
}
time = Math.max(time, lastErrorTimeMillis + backoff);
}
return time;
}
/**
* Return the last time the operation completed. Does not modify any state.
*
* @return the wall clock time when {@link #onSuccess()} was last called.
*/
public long getLastSuccessTimeMillis() {
return mStorage.getLong(PREFIX + "lastSuccessTimeMillis", 0);
}
/**
* Return the last time the operation was attempted. Does not modify any state.
*
* @return the wall clock time when {@link #onSuccess()} or {@link
* #onTransientError()} was last called.
*/
public long getLastAttemptTimeMillis() {
return Math.max(
mStorage.getLong(PREFIX + "lastSuccessTimeMillis", 0),
mStorage.getLong(PREFIX + "lastErrorTimeMillis", 0));
}
/**
* Fetch a {@link SharedPreferences} property, but force it to be before
* a certain time, updating the value if necessary. This is to recover
* gracefully from clock rollbacks which could otherwise strand our timers.
*
* @param name of SharedPreferences key
* @param max time to allow in result
* @return current value attached to key (default 0), limited by max
*/
private long getTimeBefore(String name, long max) {
long time = mStorage.getLong(name, 0);
if (time > max) {
time = max;
SharedPreferencesCompat.apply(mStorage.edit().putLong(name, time));
}
return time;
}
/**
* Request an operation to be performed at a certain time. The actual
* scheduled time may be affected by error backoff logic and defined
* minimum intervals. Use {@link Long#MAX_VALUE} to disable triggering.
*
* @param millis wall clock time ({@link System#currentTimeMillis()}) to
* trigger another operation; 0 to trigger immediately
*/
public void setTriggerTimeMillis(long millis) {
SharedPreferencesCompat.apply(
mStorage.edit().putLong(PREFIX + "triggerTimeMillis", millis));
}
/**
* Forbid any operations until after a certain (absolute) time.
* Limited by {@link Options#maxMoratoriumMillis}.
*
* @param millis wall clock time ({@link System#currentTimeMillis()})
* when operations should be allowed again; 0 to remove moratorium
*/
public void setMoratoriumTimeMillis(long millis) {
SharedPreferencesCompat.apply(mStorage.edit()
.putLong(PREFIX + "moratoriumTimeMillis", millis)
.putLong(PREFIX + "moratoriumSetTimeMillis", currentTimeMillis()));
}
/**
* Forbid any operations until after a certain time, as specified in
* the format used by the HTTP "Retry-After" header.
* Limited by {@link Options#maxMoratoriumMillis}.
*
* @param retryAfter moratorium time in HTTP format
* @return true if a time was successfully parsed
*/
public boolean setMoratoriumTimeHttp(String retryAfter) {
try {
long ms = Long.valueOf(retryAfter) * 1000;
setMoratoriumTimeMillis(ms + currentTimeMillis());
return true;
} catch (NumberFormatException nfe) {
try {
setMoratoriumTimeMillis(AndroidHttpClient.parseDate(retryAfter));
return true;
} catch (IllegalArgumentException iae) {
return false;
}
}
}
/**
* Enable or disable all operations. When disabled, all calls to
* {@link #getNextTimeMillis} return {@link Long#MAX_VALUE}.
* Commonly used when data network availability goes up and down.
*
* @param enabled if operations can be performed
*/
public void setEnabledState(boolean enabled) {
SharedPreferencesCompat.apply(
mStorage.edit().putBoolean(PREFIX + "enabledState", enabled));
}
/**
* Report successful completion of an operation. Resets all error
* counters, clears any trigger directives, and records the success.
*/
public void onSuccess() {
resetTransientError();
resetPermanentError();
SharedPreferencesCompat.apply(mStorage.edit()
.remove(PREFIX + "errorCount")
.remove(PREFIX + "lastErrorTimeMillis")
.remove(PREFIX + "permanentError")
.remove(PREFIX + "triggerTimeMillis")
.putLong(PREFIX + "lastSuccessTimeMillis", currentTimeMillis()));
}
/**
* Report a transient error (usually a network failure). Increments
* the error count and records the time of the latest error for backoff
* purposes.
*/
public void onTransientError() {
SharedPreferences.Editor editor = mStorage.edit();
editor.putLong(PREFIX + "lastErrorTimeMillis", currentTimeMillis());
editor.putInt(PREFIX + "errorCount",
mStorage.getInt(PREFIX + "errorCount", 0) + 1);
SharedPreferencesCompat.apply(editor);
}
/**
* Reset all transient error counts, allowing the next operation to proceed
* immediately without backoff. Commonly used on network state changes, when
* partial progress occurs (some data received), and in other circumstances
* where there is reason to hope things might start working better.
*/
public void resetTransientError() {
SharedPreferencesCompat.apply(mStorage.edit().remove(PREFIX + "errorCount"));
}
/**
* Report a permanent error that will not go away until further notice.
* No operation will be scheduled until {@link #resetPermanentError()}
* is called. Commonly used for authentication failures (which are reset
* when the accounts database is updated).
*/
public void onPermanentError() {
SharedPreferencesCompat.apply(mStorage.edit().putBoolean(PREFIX + "permanentError", true));
}
/**
* Reset any permanent error status set by {@link #onPermanentError},
* allowing operations to be scheduled as normal.
*/
public void resetPermanentError() {
SharedPreferencesCompat.apply(mStorage.edit().remove(PREFIX + "permanentError"));
}
/**
* Return a string description of the scheduler state for debugging.
*/
public String toString() {
StringBuilder out = new StringBuilder("[OperationScheduler:");
TreeMap<String, Object> copy = new TreeMap<String, Object>(mStorage.getAll()); // Sort keys
for (Map.Entry<String, Object> e : copy.entrySet()) {
String key = e.getKey();
if (key.startsWith(PREFIX)) {
if (key.endsWith("TimeMillis")) {
Time time = new Time();
time.set((Long) e.getValue());
out.append(" ").append(key.substring(PREFIX.length(), key.length() - 10));
out.append("=").append(time.format("%Y-%m-%d/%H:%M:%S"));
} else {
out.append(" ").append(key.substring(PREFIX.length()));
Object v = e.getValue();
if (v == null) {
out.append("=(null)");
} else {
out.append("=").append(v.toString());
}
}
}
}
return out.append("]").toString();
}
/**
* Gets the current time. Can be overridden for unit testing.
*
* @return {@link System#currentTimeMillis()}
*/
protected long currentTimeMillis() {
return System.currentTimeMillis();
}
}
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