Android missing data investigation and fixes

Data upload: do files ever fail to upload and get stuck on the phone?

During our testing, we did not observe any files get stuck on the phone and fail to upload to the server. However, we did find and fix several code problems that could theoretically have caused this to happen:

1. When the phone joins a WiFi network, we made it immediately start uploading files: previously, the Android app only uploaded data files when a repeating timer told it to do so. This could theoretically result in files getting stuck on the phone if the repeating timer was set to a low frequency and the phone wasn’t connected to WiFi very much. We supplemented the repeating timer by adding a listener so that when the app connects to a WiFi network, it should immediately try to upload data files. This should make file upload more reliable.

2. Synchronized the file upload function: while examining the code, we realized that the function that uploads data files can be called multiple times simultaneously. This would be likelier to happen if the file upload frequency was set to a time shorter than one hour. We don’t know what could have gone wrong if the file upload function tried to upload the same file twice, although it probably wouldn’t have resulted in any data being overwritten. Nevertheless, we thought it safest to add Java’s synchronize keyword to the file upload function, which will prevent the function from being called more than once at a time. Now, if the function is called twice, the first run must complete before the second run can start.

3. Redid file upload timeout logic: the file upload function has a built-in timeout to keep it from running for too long. Previously, this timeout was set to be the file upload frequency (which is customizable for each study) minus 2.5 seconds, the idea being to prevent one call of the file upload function from overlapping with the next call. However, if the file upload frequency was set to something very low, like 10 seconds, that would mean that each file upload function would time out after 7.5 seconds. If a large file took more than 7.5 seconds to upload, it would never actually be uploaded to the server, and it would remain stuck on the phone. After adding the Java synchronize keyword to the file upload function, we no longer needed to prevent the file upload function from being called while it was still running, since even if it’s called, it shouldn’t actually start until the previous call has finished. Therefore, we hardcoded the file upload timeout to one hour, which should be long enough for the largest data files on the slowest WiFi connections. We also added functionality to log errors in both Sentry and the Android App Log file if the app ever does hit the upload timeout.

All three of these fixes are in commit 971312b, released with version 2.3.3 of the Android app.