[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 2013-04-30 14:07:40 +02:00
Родитель 7e366b69e4
Коммит 11e72d29e5
2 изменённых файлов: 127 добавлений и 49 удалений

Просмотреть файл

@ -459,13 +459,10 @@ let SessionStoreInternal = {
catch (ex) { debug("The session file is invalid: " + ex); }
}
if (this._resume_from_crash) {
// Launch background copy of the session file. Note that we do
// not have race conditions here as _SessionFile guarantees
// that any I/O operation is completed before proceeding to
// the next I/O operation.
_SessionFile.createBackupCopy();
}
// A Lazy getter for the sessionstore.js backup promise.
XPCOMUtils.defineLazyGetter(this, "_backupSessionFileOnce", function () {
return _SessionFile.createBackupCopy();
});
// at this point, we've as good as resumed the session, so we can
// clear the resume_session_once flag, if it's set
@ -3758,13 +3755,33 @@ let SessionStoreInternal = {
return;
}
let self = this;
_SessionFile.write(data).then(
function onSuccess() {
self._lastSaveTime = Date.now();
Services.obs.notifyObservers(null, "sessionstore-state-write-complete", "");
}
);
let promise;
// If "sessionstore.resume_from_crash" is true, attempt to backup the
// session file first, before writing to it.
if (this._resume_from_crash) {
// Note that we do not have race conditions here as _SessionFile
// guarantees that any I/O operation is completed before proceeding to
// the next I/O operation.
// Note backup happens only once, on initial save.
promise = this._backupSessionFileOnce;
} else {
promise = Promise.resolve();
}
// Attempt to write to the session file (potentially, depending on
// "sessionstore.resume_from_crash" preference, after successful backup).
promise = promise.then(function onSuccess() {
// Write (atomically) to a session file, using a tmp file.
return _SessionFile.write(data);
});
// Once the session file is successfully updated, save the time stamp of the
// last save and notify the observers.
promise = promise.then(() => {
this._lastSaveTime = Date.now();
Services.obs.notifyObservers(null, "sessionstore-state-write-complete",
"");
});
},
/* ........ Auxiliary Functions .............. */

Просмотреть файл

@ -49,6 +49,10 @@ XPCOMUtils.defineLazyServiceGetter(this, "Telemetry",
XPCOMUtils.defineLazyGetter(this, "gEncoder", function () {
return new TextEncoder();
});
// A decoder.
XPCOMUtils.defineLazyGetter(this, "gDecoder", function () {
return new TextDecoder();
});
this._SessionFile = {
/**
@ -144,61 +148,118 @@ let SessionFileInternal = {
*/
backupPath: OS.Path.join(OS.Constants.Path.profileDir, "sessionstore.bak"),
/**
* Utility function to safely read a file synchronously.
* @param aPath
* A path to read the file from.
* @returns string if successful, undefined otherwise.
*/
readAuxSync: function ssfi_readAuxSync(aPath) {
let text;
try {
let file = new FileUtils.File(aPath);
let chan = NetUtil.newChannel(file);
let stream = chan.open();
text = NetUtil.readInputStreamToString(stream, stream.available(),
{charset: "utf-8"});
} catch (e if e.result == Components.results.NS_ERROR_FILE_NOT_FOUND) {
// Ignore exceptions about non-existent files.
} catch (ex) {
// Any other error.
Cu.reportError(ex);
} finally {
return text;
}
},
/**
* Read the sessionstore file synchronously.
*
* This function is meant to serve as a fallback in case of race
* between a synchronous usage of the API and asynchronous
* initialization.
*
* In case if sessionstore.js file does not exist or is corrupted (something
* happened between backup and write), attempt to read the sessionstore.bak
* instead.
*/
syncRead: function ssfi_syncRead() {
let text;
let exn;
// Start measuring the duration of the synchronous read.
TelemetryStopwatch.start("FX_SESSION_RESTORE_SYNC_READ_FILE_MS");
try {
let file = new FileUtils.File(this.path);
let chan = NetUtil.newChannel(file);
let stream = chan.open();
text = NetUtil.readInputStreamToString(stream, stream.available(), {charset: "utf-8"});
} catch (e if e.result == Components.results.NS_ERROR_FILE_NOT_FOUND) {
return "";
} catch(ex) {
exn = ex;
} finally {
TelemetryStopwatch.finish("FX_SESSION_RESTORE_SYNC_READ_FILE_MS");
// First read the sessionstore.js.
let text = this.readAuxSync(this.path);
if (typeof text === "undefined") {
// If sessionstore.js does not exist or is corrupted, read sessionstore.bak.
text = this.readAuxSync(this.backupPath);
}
if (exn) {
Cu.reportError(exn);
return "";
}
return text;
// Finish the telemetry probe and return an empty string.
TelemetryStopwatch.finish("FX_SESSION_RESTORE_SYNC_READ_FILE_MS");
return text || "";
},
read: function ssfi_read() {
let refObj = {};
/**
* Utility function to safely read a file asynchronously.
* @param aPath
* A path to read the file from.
* @param aReadOptions
* Read operation options.
* |outExecutionDuration| option will be reused and can be
* incrementally updated by the worker process.
* @returns string if successful, undefined otherwise.
*/
readAux: function ssfi_readAux(aPath, aReadOptions) {
let self = this;
return TaskUtils.spawn(function task() {
TelemetryStopwatch.start("FX_SESSION_RESTORE_READ_FILE_MS", refObj);
return TaskUtils.spawn(function () {
let text;
try {
let bytes = yield OS.File.read(self.path);
text = new TextDecoder().decode(bytes);
TelemetryStopwatch.finish("FX_SESSION_RESTORE_READ_FILE_MS", refObj);
let bytes = yield OS.File.read(aPath, undefined, aReadOptions);
text = gDecoder.decode(bytes);
// If the file is read successfully, add a telemetry probe based on
// the updated duration value of the |outExecutionDuration| option.
let histogram = Telemetry.getHistogramById(
"FX_SESSION_RESTORE_READ_FILE_MS");
histogram.add(aReadOptions.outExecutionDuration);
} catch (ex if self._isNoSuchFile(ex)) {
// Ignore exceptions about non-existent files.
} catch (ex) {
if (self._isNoSuchFile(ex)) {
// The file does not exist, this is perfectly valid
TelemetryStopwatch.finish("FX_SESSION_RESTORE_READ_FILE_MS", refObj);
} else {
// Any other error: let's not measure with telemetry
TelemetryStopwatch.cancel("FX_SESSION_RESTORE_READ_FILE_MS", refObj);
Cu.reportError(ex);
}
text = "";
Cu.reportError(ex);
}
throw new Task.Result(text);
});
},
/**
* Read the sessionstore file asynchronously.
*
* In case sessionstore.js file does not exist or is corrupted (something
* happened between backup and write), attempt to read the sessionstore.bak
* instead.
*/
read: function ssfi_read() {
let self = this;
return TaskUtils.spawn(function task() {
// Specify |outExecutionDuration| option to hold the combined duration of
// the asynchronous reads off the main thread (of both sessionstore.js and
// sessionstore.bak, if necessary). If sessionstore.js does not exist or
// is corrupted, |outExecutionDuration| will register the time it took to
// attempt to read the file. It will then be subsequently incremented by
// the read time of sessionsore.bak.
let readOptions = {
outExecutionDuration: null
};
// First read the sessionstore.js.
let text = yield self.readAux(self.path, readOptions);
if (typeof text === "undefined") {
// If sessionstore.js does not exist or is corrupted, read the
// sessionstore.bak.
text = yield self.readAux(self.backupPath, readOptions);
}
// Return either the content of the sessionstore.bak if it was read
// successfully or an empty string otherwise.
throw new Task.Result(text || "");
});
},
write: function ssfi_write(aData) {
let refObj = {};
let self = this;
@ -232,7 +293,7 @@ let SessionFileInternal = {
let self = this;
return TaskUtils.spawn(function task() {
try {
yield OS.File.copy(self.path, self.backupPath, backupCopyOptions);
yield OS.File.move(self.path, self.backupPath, backupCopyOptions);
Telemetry.getHistogramById("FX_SESSION_RESTORE_BACKUP_FILE_MS").add(
backupCopyOptions.outExecutionDuration);
} catch (ex if self._isNoSuchFile(ex)) {