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/* -*- indent-tabs-mode: nil; js-indent-level: 2 -*- */
/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
/**
* Crash Monitor
*
* Monitors execution of a program to detect possible crashes. After
* program termination, the monitor can be queried during the next run
* to determine whether the last run exited cleanly or not.
*
* The monitoring is done by registering and listening for special
* notifications, or checkpoints, known to be sent by the monitored
* program as different stages in the execution are reached. As they
* are observed, these notifications are written asynchronously to a
* checkpoint file.
*
* During next program startup the crash monitor reads the checkpoint
* file from the last session. If notifications are missing, a crash
* has likely happened. By inspecting the notifications present, it is
* possible to determine what stages were reached in the program
* before the crash.
*
* Note that since the file is written asynchronously it is possible
* that a received notification is lost if the program crashes right
* after a checkpoint, but before crash monitor has been able to write
* it to disk. Thus, while the presence of a notification in the
* checkpoint file tells us that the corresponding stage was reached
* during the last run, the absence of a notification after a crash
* does not necessarily tell us that the checkpoint wasn't reached.
*/
this.EXPORTED_SYMBOLS = [ "CrashMonitor" ];
const Cu = Components.utils;
const Cr = Components.results;
Cu.import("resource://gre/modules/Services.jsm");
Cu.import("resource://gre/modules/osfile.jsm");
Cu.import("resource://gre/modules/Promise.jsm");
Cu.import("resource://gre/modules/Task.jsm");
Cu.import("resource://gre/modules/AsyncShutdown.jsm");
const NOTIFICATIONS = [
"final-ui-startup",
"sessionstore-windows-restored",
"quit-application-granted",
"quit-application",
"profile-change-net-teardown",
"profile-change-teardown",
"profile-before-change",
"sessionstore-final-state-write-complete"
];
var CrashMonitorInternal = {
/**
* Notifications received during the current session.
*
* Object where a property with a value of |true| means that the
* notification of the same name has been received at least once by
* the CrashMonitor during this session. Notifications that have not
* yet been received are not present as properties. |NOTIFICATIONS|
* lists the notifications tracked by the CrashMonitor.
*/
checkpoints: {},
/**
* Notifications received during previous session.
*
* Available after |loadPreviousCheckpoints|. Promise which resolves
* to an object containing a set of properties, where a property
* with a value of |true| means that the notification with the same
* name as the property name was received at least once last
* session.
*/
previousCheckpoints: null,
/* Deferred for AsyncShutdown blocker */
profileBeforeChangeDeferred: Promise.defer(),
/**
* Path to checkpoint file.
*
* Each time a new notification is received, this file is written to
* disc to reflect the information in |checkpoints|.
*/
path: OS.Path.join(OS.Constants.Path.profileDir, "sessionCheckpoints.json"),
/**
* Load checkpoints from previous session asynchronously.
*
* @return {Promise} A promise that resolves/rejects once loading is complete
*/
loadPreviousCheckpoints: function () {
this.previousCheckpoints = Task.spawn(function*() {
let data;
try {
data = yield OS.File.read(CrashMonitorInternal.path, { encoding: "utf-8" });
} catch (ex) {
if (!(ex instanceof OS.File.Error)) {
throw ex;
}
if (!ex.becauseNoSuchFile) {
Cu.reportError("Error while loading crash monitor data: " + ex.toString());
}
return null;
}
let notifications;
try {
notifications = JSON.parse(data);
} catch (ex) {
Cu.reportError("Error while parsing crash monitor data: " + ex);
return null;
}
// If `notifications` isn't an object, then the monitor data isn't valid.
if (Object(notifications) !== notifications) {
Cu.reportError("Error while parsing crash monitor data: invalid monitor data");
return null;
}
return Object.freeze(notifications);
});
return this.previousCheckpoints;
}
};
this.CrashMonitor = {
/**
* Notifications received during previous session.
*
* Return object containing the set of notifications received last
* session as keys with values set to |true|.
*
* @return {Promise} A promise resolving to previous checkpoints
*/
get previousCheckpoints() {
if (!CrashMonitorInternal.initialized) {
throw new Error("CrashMonitor must be initialized before getting previous checkpoints");
}
return CrashMonitorInternal.previousCheckpoints
},
/**
* Initialize CrashMonitor.
*
* Should only be called from the CrashMonitor XPCOM component.
*
* @return {Promise}
*/
init: function () {
if (CrashMonitorInternal.initialized) {
throw new Error("CrashMonitor.init() must only be called once!");
}
let promise = CrashMonitorInternal.loadPreviousCheckpoints();
// Add "profile-after-change" to checkpoint as this method is
// called after receiving it
CrashMonitorInternal.checkpoints["profile-after-change"] = true;
NOTIFICATIONS.forEach(function (aTopic) {
Services.obs.addObserver(this, aTopic, false);
}, this);
// Add shutdown blocker for profile-before-change
OS.File.profileBeforeChange.addBlocker(
"CrashMonitor: Writing notifications to file after receiving profile-before-change",
CrashMonitorInternal.profileBeforeChangeDeferred.promise,
() => this.checkpoints
);
CrashMonitorInternal.initialized = true;
return promise;
},
/**
* Handle registered notifications.
*
* Update checkpoint file for every new notification received.
*/
observe: function (aSubject, aTopic, aData) {
if (!(aTopic in CrashMonitorInternal.checkpoints)) {
// If this is the first time this notification is received,
// remember it and write it to file
CrashMonitorInternal.checkpoints[aTopic] = true;
Task.spawn(function* () {
try {
let data = JSON.stringify(CrashMonitorInternal.checkpoints);
/* Write to the checkpoint file asynchronously, off the main
* thread, for performance reasons. Note that this means
* that there's not a 100% guarantee that the file will be
* written by the time the notification completes. The
* exception is profile-before-change which has a shutdown
* blocker. */
yield OS.File.writeAtomic(
CrashMonitorInternal.path,
data, {tmpPath: CrashMonitorInternal.path + ".tmp"});
} finally {
// Resolve promise for blocker
if (aTopic == "profile-before-change") {
CrashMonitorInternal.profileBeforeChangeDeferred.resolve();
}
}
});
}
if (NOTIFICATIONS.every(elem => elem in CrashMonitorInternal.checkpoints)) {
// All notifications received, unregister observers
NOTIFICATIONS.forEach(function (aTopic) {
Services.obs.removeObserver(this, aTopic);
}, this);
}
}
};
Object.freeze(this.CrashMonitor);
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