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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.
*/
import { PrivateBrowsingUtils } from "resource://gre/modules/PrivateBrowsingUtils.sys.mjs";
const SESSIONSTORE_WINDOWS_RESTORED_TOPIC = "sessionstore-windows-restored";
const SESSIONSTORE_FINAL_STATE_WRITE_COMPLETE_TOPIC =
"sessionstore-final-state-write-complete";
const NOTIFICATIONS = [
"final-ui-startup",
SESSIONSTORE_WINDOWS_RESTORED_TOPIC,
"quit-application-granted",
"quit-application",
"profile-change-net-teardown",
"profile-change-teardown",
SESSIONSTORE_FINAL_STATE_WRITE_COMPLETE_TOPIC,
];
const SHUTDOWN_PHASES = ["profile-before-change"];
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: {},
/**
* A deferred promise that resolves when all checkpoints have been written.
*/
sessionStoreFinalWriteComplete: Promise.withResolvers(),
/**
* 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,
/**
* Path to checkpoint file.
*
* Each time a new notification is received, this file is written to
* disc to reflect the information in |checkpoints|.
*/
path: PathUtils.join(
Services.dirsvc.get("ProfD", Ci.nsIFile).path,
"sessionCheckpoints.json"
),
/**
* Load checkpoints from previous session asynchronously.
*
* @return {Promise} A promise that resolves/rejects once loading is complete
*/
loadPreviousCheckpoints() {
this.previousCheckpoints = (async function () {
let notifications;
try {
notifications = await IOUtils.readJSON(CrashMonitorInternal.path);
} catch (ex) {
// Ignore file not found errors, but report all others.
if (ex.name !== "NotFoundError") {
console.error("Error while loading crash monitor data:", ex.message);
}
return null;
}
// If `notifications` isn't an object, then the monitor data isn't valid.
if (Object(notifications) !== notifications) {
console.error(
"Error while parsing crash monitor data: invalid monitor data"
);
return null;
}
return Object.freeze(notifications);
})();
return this.previousCheckpoints;
},
};
export var 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() {
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);
}, this);
// Add shutdown blocker for profile-before-change
IOUtils.profileBeforeChange.addBlocker(
"CrashMonitor: Writing notifications to file after receiving profile-before-change and awaiting all checkpoints written",
async () => {
await this.writeCheckpoint("profile-before-change");
// If SessionStore has not initialized, we don't want to wait for
// checkpoints that we won't hit, or we'll crash the browser during
// async shutdown.
if (
!PrivateBrowsingUtils.permanentPrivateBrowsing &&
CrashMonitorInternal.checkpoints[SESSIONSTORE_WINDOWS_RESTORED_TOPIC]
) {
await CrashMonitorInternal.sessionStoreFinalWriteComplete.promise;
}
},
() => CrashMonitorInternal.checkpoints
);
CrashMonitorInternal.initialized = true;
return promise;
},
/**
* Handle registered notifications.
*
* Update checkpoint file for every new notification received.
*/
observe(aSubject, aTopic, aData) {
this.writeCheckpoint(aTopic);
if (
NOTIFICATIONS.every(elem => elem in CrashMonitorInternal.checkpoints) &&
SHUTDOWN_PHASES.every(elem => elem in CrashMonitorInternal.checkpoints)
) {
// All notifications received, unregister observers
NOTIFICATIONS.forEach(function (aTopic) {
Services.obs.removeObserver(this, aTopic);
}, this);
}
if (aTopic === SESSIONSTORE_FINAL_STATE_WRITE_COMPLETE_TOPIC) {
CrashMonitorInternal.sessionStoreFinalWriteComplete.resolve();
}
},
async writeCheckpoint(aCheckpoint) {
if (!(aCheckpoint in CrashMonitorInternal.checkpoints)) {
// If this is the first time this notification is received,
// remember it and write it to file
CrashMonitorInternal.checkpoints[aCheckpoint] = true;
/* 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. */
await IOUtils.writeJSON(
CrashMonitorInternal.path,
CrashMonitorInternal.checkpoints,
{
tmpPath: CrashMonitorInternal.path + ".tmp",
}
);
}
},
};
Object.freeze(CrashMonitor);
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