A background URLSession with identifier already exists

Question

I have an S3Service which is a singleton that manages all the S3 related uploads and downloads. When I upload the first image it works fine but if I try to upload an Image consecutively It gives me this warning and the completion block never gets called.

A background URLSession with identifier com.amazonaws.AWSS3TransferUtility.Identifier.TransferManager already exists.

This is how I upload method looks:

if let data = image.jpegData(compressionQuality: 0.5) {
        let transferUtility = AWSS3TransferUtility.s3TransferUtility(forKey: S3Service.TRANSFER_MANAGER_KEY)
        transferUtility.uploadUsingMultiPart(data: data, bucket: EnvironmentUtils.getBucketName(), key: filename, contentType: "image/jpg", expression: nil, completionHandler: { task,error in

            if let error = error {
                print(error.localizedDescription)
            } else {
                print("Image upload success")
            }
        })
}

@CalebKleveter It has the above mentioned code in an upload method, a method to register AWSS3 Transfer utility, and a method to unregister it. — Agent Smith, Dec 13 '18 at 18:12

score 5 · Answer 1 · answered Dec 14 '18 at 10:27

The call to register transfer utility AWSS3TransferUtility.register(with: serviceconfig, forKey: KEY) was causing the above issue. There are two things that should be kept in mind.

The AWSS3TransferUtility should be registered only once per Application session. Then we can use AWSS3TransferUtility.S3TransferUtilityForKey to get the instance wherever needed.
If these are for different users within the app, ( e.g. sign-up) and if we want to keep AWSS3TransferUtility separate for each user, register AWSS3TransferUtility with a different key (preferably the same key for the same user) and look up using that key.

A background URLSession with identifier already exists

1 Answers1