UnauthorizedAccessException: Access is denied (0x80070005).<\/figcaption><\/figure>\nLe probl\u00e8me rencontr\u00e9 intervient lorsque plusieurs images d’une liste essaient d’enregistrer des \u00e9l\u00e9ments dans l’Isolated Storage en m\u00eame temps.<\/p>\n
Pourtant le code me paraissait plut\u00f4t correct ?<\/p>\n
public async Task<string> SaveImageInStorageAsyncBad(string urlImage, object datas)\n{\n if (!String.IsNullOrEmpty(urlImage) && datas is byte[])\n {\n string id = urlImage;\n \n var localFolder = Windows.Storage.ApplicationData.Current.LocalFolder;\n var folder = await localFolder.CreateFolderAsync(\"DataCache\", Windows.Storage.CreationCollisionOption.OpenIfExists);\n var file = await folder.CreateFileAsync(id, Windows.Storage.CreationCollisionOption.ReplaceExisting);\n var stream = await file.OpenStreamForWriteAsync();\n using (var outStream = stream)\n {\n var dataWriter = new Windows.Storage.Streams.DataWriter(outStream.AsOutputStream());\n dataWriter.WriteBytes(datas as byte[]);\n await dataWriter.StoreAsync();\n return id;\n }\n \n }\n else\n return String.Empty;\n}\n<\/pre>\n\u00a0FlushAsync()<\/h1>\n
La premi\u00e8re chose qu’il manque est un await dataWriter.FlushAsync() juste apr\u00e8s le StoreAsync().<\/p>\n
En effet, nous utilisons un Stream pour \u00e9crire l’image.<\/p>\n
Le Flush permet de s’assurer que tout le stream va \u00eatre \u00e9crit correctement avant de continuer.<\/p>\n
Verrou – Lock ?<\/h1>\n
Mais le Flush ne suffit pas l’erreur est encore rencontr\u00e9e. Il va falloir prot\u00e9ger le code en \u00e9vitant une \u00e9criture parall\u00e8le des images.<\/p>\n
En mode Synchrone un Lock aurait p\u00fb \u00eatre utilis\u00e9 mais nous somme dans un traitement asynchrone.<\/p>\n
L’utilisation du Lock est interdite car emp\u00eache le thread de continuer. Le compilateur l’indique clairement.<\/p>\n
Pour assurer une \u00e9criture \u00e0 la fois, nous allons utiliser l’objet SemaphoreSlim.<\/p>\n
Il faut initialiser\u00a0cet objet de la fa\u00e7on suivante :<\/p>\n
private SemaphoreSlim _syncLock = new SemaphoreSlim(1);<\/pre>\nLe 1\u00a0en param\u00e8tre indique que nous ne souhaitons q’un seul acc\u00e8s concurent.<\/p>\n
Pour blocker les acc\u00e8s concurent on appelle la m\u00e9thode :<\/p>\n
await _syncLock.WaitAsync();<\/pre>\nPour rendre le block<\/p>\n
_syncLock.Release();<\/pre>\n <\/p>\n
Le code final qui fonctionne sans erreur ressemble maintenant \u00e0 ceci :<\/p>\n
A noter\u00a0 : l’utilisation du try … finally pour assurer le d\u00e9verrouillage m\u00eame en cas d’anomalies.<\/p>\n
public async Task<string> SaveImageInStorageAsync(string urlImage, object datas)\n{\n if (!String.IsNullOrEmpty(urlImage) && datas is byte[])\n {\n string id = GetIdStorage(urlImage, savedName);\n await _syncLock.WaitAsync();\n try\n {\n var localFolder = Windows.Storage.ApplicationData.Current.LocalFolder;\n var folder = await localFolder.CreateFolderAsync(\"DataCache\", Windows.Storage.CreationCollisionOption.OpenIfExists);\n var file = await folder.CreateFileAsync(id, Windows.Storage.CreationCollisionOption.ReplaceExisting);\n var stream = await file.OpenStreamForWriteAsync();\n using (var outStream = stream)\n {\n var dataWriter = new Windows.Storage.Streams.DataWriter(outStream.AsOutputStream());\n dataWriter.WriteBytes(datas as byte[]);\n await dataWriter.StoreAsync();\n await dataWriter.FlushAsync();\n outStream.Dispose();\n return id;\n }\n }\n finally\n {\n _syncLock.Release();\n }\n }\n else\n return String.Empty;\n}\n<\/pre>\n <\/p>\n
Voici donc un m\u00e9canisme fort utile pour am\u00e9liorer la r\u00e9activit\u00e9 de vos applications Windows et Windows Phone<\/p>\n","protected":false},"excerpt":{"rendered":"
Ecriture dans l’isolated Storage d’un fichier image Il est parfois fort utile de sauvegarder les images provenant d’un serveur HTTP dans un cache afin d’\u00e9viter de les charger \u00e0 chaque fois. En impl\u00e9mentant\u00a0ce syst\u00e8me de cache en asynchrone, je me suis rendu compte de plusieurs probl\u00e8mes causant syst\u00e9matiquement un UnauthorizedAccessException: Access is denied (0x80070005).<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[59,62,63],"tags":[68,69,70,132,133,134,58,8],"aioseo_notices":[],"_links":{"self":[{"href":"https:\/\/bratched.com\/fr\/wp-json\/wp\/v2\/posts\/782"}],"collection":[{"href":"https:\/\/bratched.com\/fr\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/bratched.com\/fr\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/bratched.com\/fr\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/bratched.com\/fr\/wp-json\/wp\/v2\/comments?post=782"}],"version-history":[{"count":0,"href":"https:\/\/bratched.com\/fr\/wp-json\/wp\/v2\/posts\/782\/revisions"}],"wp:attachment":[{"href":"https:\/\/bratched.com\/fr\/wp-json\/wp\/v2\/media?parent=782"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/bratched.com\/fr\/wp-json\/wp\/v2\/categories?post=782"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/bratched.com\/fr\/wp-json\/wp\/v2\/tags?post=782"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
![\"Ecriture](\"http:\/\/dev.bratched.fr\/fr\/wp-content\/uploads\/sites\/2\/2014\/11\/IsolatedStorage.png\")
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