зеркало из https://github.com/mozilla/gecko-dev.git
[PATCH 1/2] Bug 833286 - added improvements to atomic backup of sessionstore.js. r=yoric, ttaubert
--- .../components/sessionstore/src/SessionStore.jsm | 45 +++++-- .../components/sessionstore/src/_SessionFile.jsm | 131 ++++++++++++++----- 2 files changed, 127 insertions(+), 49 deletions(-)
This commit is contained in:
Yura Zenevich
Родитель
7e366b69e4
Коммит
11e72d29e5
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@ -459,13 +459,10 @@ let SessionStoreInternal = {
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catch (ex) { debug("The session file is invalid: " + ex); }
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}
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if (this._resume_from_crash) {
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// Launch background copy of the session file. Note that we do
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// not have race conditions here as _SessionFile guarantees
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// that any I/O operation is completed before proceeding to
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// the next I/O operation.
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_SessionFile.createBackupCopy();
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}
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// A Lazy getter for the sessionstore.js backup promise.
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XPCOMUtils.defineLazyGetter(this, "_backupSessionFileOnce", function () {
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return _SessionFile.createBackupCopy();
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});
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// at this point, we've as good as resumed the session, so we can
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// clear the resume_session_once flag, if it's set
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@ -3758,13 +3755,33 @@ let SessionStoreInternal = {
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return;
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}
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let self = this;
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_SessionFile.write(data).then(
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function onSuccess() {
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self._lastSaveTime = Date.now();
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Services.obs.notifyObservers(null, "sessionstore-state-write-complete", "");
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let promise;
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// If "sessionstore.resume_from_crash" is true, attempt to backup the
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// session file first, before writing to it.
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if (this._resume_from_crash) {
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// Note that we do not have race conditions here as _SessionFile
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// guarantees that any I/O operation is completed before proceeding to
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// the next I/O operation.
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// Note backup happens only once, on initial save.
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promise = this._backupSessionFileOnce;
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} else {
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promise = Promise.resolve();
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}
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);
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// Attempt to write to the session file (potentially, depending on
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// "sessionstore.resume_from_crash" preference, after successful backup).
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promise = promise.then(function onSuccess() {
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// Write (atomically) to a session file, using a tmp file.
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return _SessionFile.write(data);
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});
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// Once the session file is successfully updated, save the time stamp of the
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// last save and notify the observers.
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promise = promise.then(() => {
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this._lastSaveTime = Date.now();
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Services.obs.notifyObservers(null, "sessionstore-state-write-complete",
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"");
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});
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},
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/* ........ Auxiliary Functions .............. */
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@ -49,6 +49,10 @@ XPCOMUtils.defineLazyServiceGetter(this, "Telemetry",
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XPCOMUtils.defineLazyGetter(this, "gEncoder", function () {
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return new TextEncoder();
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});
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// A decoder.
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XPCOMUtils.defineLazyGetter(this, "gDecoder", function () {
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return new TextDecoder();
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});
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this._SessionFile = {
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/**
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@ -144,61 +148,118 @@ let SessionFileInternal = {
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*/
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backupPath: OS.Path.join(OS.Constants.Path.profileDir, "sessionstore.bak"),
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/**
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* Utility function to safely read a file synchronously.
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* @param aPath
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* A path to read the file from.
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* @returns string if successful, undefined otherwise.
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*/
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readAuxSync: function ssfi_readAuxSync(aPath) {
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let text;
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try {
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let file = new FileUtils.File(aPath);
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let chan = NetUtil.newChannel(file);
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let stream = chan.open();
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text = NetUtil.readInputStreamToString(stream, stream.available(),
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{charset: "utf-8"});
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} catch (e if e.result == Components.results.NS_ERROR_FILE_NOT_FOUND) {
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// Ignore exceptions about non-existent files.
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} catch (ex) {
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// Any other error.
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Cu.reportError(ex);
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} finally {
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return text;
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}
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},
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/**
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* Read the sessionstore file synchronously.
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*
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* This function is meant to serve as a fallback in case of race
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* between a synchronous usage of the API and asynchronous
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* initialization.
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*
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* In case if sessionstore.js file does not exist or is corrupted (something
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* happened between backup and write), attempt to read the sessionstore.bak
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* instead.
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*/
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syncRead: function ssfi_syncRead() {
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let text;
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let exn;
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// Start measuring the duration of the synchronous read.
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TelemetryStopwatch.start("FX_SESSION_RESTORE_SYNC_READ_FILE_MS");
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try {
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let file = new FileUtils.File(this.path);
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let chan = NetUtil.newChannel(file);
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let stream = chan.open();
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text = NetUtil.readInputStreamToString(stream, stream.available(), {charset: "utf-8"});
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} catch (e if e.result == Components.results.NS_ERROR_FILE_NOT_FOUND) {
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return "";
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} catch(ex) {
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exn = ex;
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} finally {
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// First read the sessionstore.js.
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let text = this.readAuxSync(this.path);
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if (typeof text === "undefined") {
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// If sessionstore.js does not exist or is corrupted, read sessionstore.bak.
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text = this.readAuxSync(this.backupPath);
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}
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// Finish the telemetry probe and return an empty string.
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TelemetryStopwatch.finish("FX_SESSION_RESTORE_SYNC_READ_FILE_MS");
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}
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if (exn) {
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Cu.reportError(exn);
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return "";
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}
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return text;
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return text || "";
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},
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read: function ssfi_read() {
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let refObj = {};
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/**
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* Utility function to safely read a file asynchronously.
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* @param aPath
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* A path to read the file from.
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* @param aReadOptions
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* Read operation options.
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* |outExecutionDuration| option will be reused and can be
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* incrementally updated by the worker process.
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* @returns string if successful, undefined otherwise.
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*/
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readAux: function ssfi_readAux(aPath, aReadOptions) {
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let self = this;
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return TaskUtils.spawn(function task() {
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TelemetryStopwatch.start("FX_SESSION_RESTORE_READ_FILE_MS", refObj);
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return TaskUtils.spawn(function () {
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let text;
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try {
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let bytes = yield OS.File.read(self.path);
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text = new TextDecoder().decode(bytes);
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TelemetryStopwatch.finish("FX_SESSION_RESTORE_READ_FILE_MS", refObj);
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let bytes = yield OS.File.read(aPath, undefined, aReadOptions);
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text = gDecoder.decode(bytes);
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// If the file is read successfully, add a telemetry probe based on
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// the updated duration value of the |outExecutionDuration| option.
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let histogram = Telemetry.getHistogramById(
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"FX_SESSION_RESTORE_READ_FILE_MS");
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histogram.add(aReadOptions.outExecutionDuration);
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} catch (ex if self._isNoSuchFile(ex)) {
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// Ignore exceptions about non-existent files.
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} catch (ex) {
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if (self._isNoSuchFile(ex)) {
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// The file does not exist, this is perfectly valid
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TelemetryStopwatch.finish("FX_SESSION_RESTORE_READ_FILE_MS", refObj);
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} else {
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// Any other error: let's not measure with telemetry
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TelemetryStopwatch.cancel("FX_SESSION_RESTORE_READ_FILE_MS", refObj);
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Cu.reportError(ex);
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}
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text = "";
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}
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throw new Task.Result(text);
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});
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},
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/**
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* Read the sessionstore file asynchronously.
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*
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* In case sessionstore.js file does not exist or is corrupted (something
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* happened between backup and write), attempt to read the sessionstore.bak
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* instead.
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*/
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read: function ssfi_read() {
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let self = this;
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return TaskUtils.spawn(function task() {
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// Specify |outExecutionDuration| option to hold the combined duration of
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// the asynchronous reads off the main thread (of both sessionstore.js and
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// sessionstore.bak, if necessary). If sessionstore.js does not exist or
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// is corrupted, |outExecutionDuration| will register the time it took to
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// attempt to read the file. It will then be subsequently incremented by
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// the read time of sessionsore.bak.
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let readOptions = {
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outExecutionDuration: null
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};
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// First read the sessionstore.js.
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let text = yield self.readAux(self.path, readOptions);
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if (typeof text === "undefined") {
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// If sessionstore.js does not exist or is corrupted, read the
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// sessionstore.bak.
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text = yield self.readAux(self.backupPath, readOptions);
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}
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// Return either the content of the sessionstore.bak if it was read
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// successfully or an empty string otherwise.
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throw new Task.Result(text || "");
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});
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},
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write: function ssfi_write(aData) {
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let refObj = {};
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let self = this;
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@ -232,7 +293,7 @@ let SessionFileInternal = {
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let self = this;
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return TaskUtils.spawn(function task() {
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try {
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yield OS.File.copy(self.path, self.backupPath, backupCopyOptions);
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yield OS.File.move(self.path, self.backupPath, backupCopyOptions);
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Telemetry.getHistogramById("FX_SESSION_RESTORE_BACKUP_FILE_MS").add(
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backupCopyOptions.outExecutionDuration);
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} catch (ex if self._isNoSuchFile(ex)) {
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