Microsoft.Azure.WebJobs.Script.FileTraceWriter.SetNewLogFile C# (CSharp) Method

        internal void SetNewLogFile()
        {
            // purge any log files (regardless of instance ID) whose last write time was earlier
            // than our retention policy
            var filesToPurge = _logDirectory.GetFiles("*.log").Where(p => (DateTime.UtcNow - p.LastWriteTimeUtc).TotalDays > LastModifiedCutoffDays);
            DeleteFiles(filesToPurge);

            // we include a machine identifier in the log file name to ensure we don't have any
            // log file contention between scaled out instances
            string filePath = Path.Combine(_logFilePath, string.Format(CultureInfo.InvariantCulture, "{0}-{1}.log", DateTime.UtcNow.ToString("yyyy-MM-ddTHH-mm-ssK"), _instanceId));
            _currentLogFileInfo = new FileInfo(filePath);
        }

        public async Task SetNewLogFile_PurgesOldLogFiles()
        {
            DirectoryInfo directory = new DirectoryInfo(_logFilePath);
            directory.Create();

            // below test expects the retention days to be set to 1
            Assert.Equal(1, FileTraceWriter.LastModifiedCutoffDays);

            // create some log files
            List<FileInfo> logFiles = new List<FileInfo>();
            int initialCount = 5;
            for (int i = 0; i < initialCount; i++)
            {
                string fileName = string.Format("{0}-{1}.log", i, FileTraceWriter.GetInstanceId());
                string path = Path.Combine(_logFilePath, fileName);
                Thread.Sleep(50);
                File.WriteAllText(path, "Test Logs");
                logFiles.Add(new FileInfo(path));
            }

            // mark some of the files as old - we expect
            // all of these to be purged
            File.SetLastWriteTime(logFiles[2].FullName, DateTime.Now.Subtract(TimeSpan.FromDays(1)));
            File.SetLastWriteTime(logFiles[1].FullName, DateTime.Now.Subtract(TimeSpan.FromDays(1)));
            File.SetLastWriteTime(logFiles[0].FullName, DateTime.Now.Subtract(TimeSpan.FromDays(2)));

            var files = directory.GetFiles().OrderByDescending(p => p.LastWriteTime).ToArray();
            Assert.Equal(initialCount, files.Length);

            FileTraceWriter traceWriter = new FileTraceWriter(_logFilePath, TraceLevel.Verbose);
            traceWriter.SetNewLogFile();

            files = directory.GetFiles().OrderByDescending(p => p.LastWriteTime).ToArray();

            await TestHelpers.Await(() =>
            {
                files = directory.GetFiles().OrderByDescending(p => p.LastWriteTime).ToArray();
                return files.Length == 2;
            }, timeout: 2000);

            // verify the correct log files were purged and the 2
            // most recent files were retained
            Assert.True(files[0].Name.StartsWith("4"));
            Assert.True(files[1].Name.StartsWith("3"));
        }