"Read Timed out" while continuously uploading file

Question

I am using 2 FileTransferClient.uploadFile() statements within a for loop to continously upload 2 kinds of files to an FTP server.
I get a SocketTimeoutException with a message "Read timed out" whenever it hits the second uploadFile() stmt within the for loop.
But when I introduce a sleep statement between the uploadFile() stmts, it works fine.

The code is as follows,

for(some condition)
{

//some stmts
...

docName = buff.toString() + Constants.OUT;
ftpClient.uploadFile(srcFolder + docName, docName);
logger.debug("Uploaded document to FTP server : " + docName);

//Starting from 500 millis, I reduced the interval and reached this min level.
//I tested for filesize range between 2 KB and 128MB.
//Filesize does not seem to have an impact on the interval, but with an
//interval of 5 millis a random file got the "Read timed out" error and not
//the 128 MB file (the max sized file).
Thread.sleep(10);

indName = buff.toString() + Constants.IND;
ftpClient.uploadFile(srcFolder + indName, indName);
logger.debug("Uploaded document metadata to FTP server : " + indName);

//some stmts
...
}

The stack trace is as follows,

java.net.SocketTimeoutException: Read timed out
at java.net.SocketInputStream.socketRead0(Native Method)
at java.net.SocketInputStream.read(SocketInputStream.java:129)
at sun.nio.cs.StreamDecoder$CharsetSD.readBytes(StreamDecoder.java:408)
at sun.nio.cs.StreamDecoder$CharsetSD.implRead(StreamDecoder.java:450)
at sun.nio.cs.StreamDecoder.read(StreamDecoder.java:182)
at java.io.InputStreamReader.read(InputStreamReader.java:167)
at java.io.BufferedReader.fill(BufferedReader.java:136)
at java.io.BufferedReader.readLine(BufferedReader.java:299)
at java.io.BufferedReader.readLine(BufferedReader.java:362)
at com.enterprisedt.net.ftp.FTPControlSocket.readReply(FTPControlSocket.java:847)
at com.enterprisedt.net.ftp.FTPControlSocket.sendCommand(FTPControlSocket.java:815)
at com.enterprisedt.net.ftp.FTPControlSocket.setDataPort(FTPControlSocket.java:649)
at com.enterprisedt.net.ftp.FTPControlSocket.sendPORTCommand(FTPControlSocket.java:527)
at com.enterprisedt.net.ftp.FTPControlSocket.createDataSocketActive(FTPControlSocket.java:508)
at com.enterprisedt.net.ftp.FTPControlSocket.createDataSocket(FTPControlSocket.java:479)
at com.enterprisedt.net.ftp.FTPClient.setupDataSocket(FTPClient.java:2160)
at com.enterprisedt.net.ftp.FTPClient.initPut(FTPClient.java:2195)
at com.enterprisedt.net.ftp.FTPClient.putData(FTPClient.java:2278)
at com.enterprisedt.net.ftp.FTPClient.put(FTPClient.java:2021)
at com.enterprisedt.net.ftp.FTPClient.put(FTPClient.java:2003)
at com.enterprisedt.net.ftp.FileTransferClient.uploadFile(FileTransferClient.java:593)
at com.enterprisedt.net.ftp.FileTransferClient.uploadFile(FileTransferClient.java:567)
at com.ssc.reti.transfer.TransferHandler.transfer(TransferHandler.java:257)
at com.ssc.reti.transfer.TransferHandler.main(TransferHandler.java:339)

I also enabled the EDT logger and got the following log stmts,
DEBUG [FTPClient] 4 Jan 2008 15:20:29.331 : Class: com.enterprisedt.net.ftp.FTPClient
Version: 2.0.0
Build timestamp: 20-Dec-2007 11:27:53 EST
Java version: 1.4.2_08
CLASSPATH: C:\VMFS\J2EE\RETI\bin;C:\VMFS\J2EE\RETI\lib\log4j.jar;
C:\Documentum\Shared\dfcbase.jar;C:\Documentum\Shared\dfc.jar;
C:\senthil\softwares\edtftpj-2.0.0\lib\edtftpj.jar
OS name: Windows XP
OS arch: x86
OS version: 5.1

DEBUG [FileTransferClient] 4 Jan 2008 15:20:29.347 : Configured client
DEBUG [FTPClient] 4 Jan 2008 15:20:29.347 : Connecting to /10.46.37.31:21
DEBUG [SocketUtils] 4 Jan 2008 15:20:29.362 : Invoking connect with timeout=60000
DEBUG [SocketUtils] 4 Jan 2008 15:20:29.362 : Connected successfully
DEBUG [FTPControlSocket] 4 Jan 2008 15:20:29.362 : 220 Golden FTP Server ready v3.66
DEBUG [FileTransferClient] 4 Jan 2008 15:20:29.378 : Client connected
DEBUG [FileTransferClient] 4 Jan 2008 15:20:29.378 : Logging in
DEBUG [FTPControlSocket] 4 Jan 2008 15:20:29.378 : ---> USER anonymous
DEBUG [FTPControlSocket] 4 Jan 2008 15:20:29.378 : 331 User name okay, need password.
DEBUG [FTPControlSocket] 4 Jan 2008 15:20:29.378 : ---> PASS ********
DEBUG [FTPControlSocket] 4 Jan 2008 15:20:29.378 : 230 User logged in, proceed.
DEBUG [FileTransferClient] 4 Jan 2008 15:20:29.378 : Logged in
DEBUG [FTPControlSocket] 4 Jan 2008 15:20:29.378 : ---> TYPE I
DEBUG [FTPControlSocket] 4 Jan 2008 15:20:29.378 : 200 Type set to I.
DEBUG [FTPControlSocket] 4 Jan 2008 15:20:29.378 : ---> TYPE I
DEBUG [FTPControlSocket] 4 Jan 2008 15:20:29.378 : 200 Type set to I.
DEBUG [FTPControlSocket] 4 Jan 2008 15:20:29.378 : ---> CWD FTP
DEBUG [FTPControlSocket] 4 Jan 2008 15:20:29.393 : 250 CWD Command successful.
DEBUG [FTPControlSocket] 4 Jan 2008 15:20:29.440 : ListenOnAllInterfaces=true
DEBUG [FTPControlSocket] 4 Jan 2008 15:20:29.440 : ---> PORT 10,46,37,31,9,235
DEBUG [FTPControlSocket] 4 Jan 2008 15:20:29.440 : 200 PORT Command successful.
DEBUG [FTPControlSocket] 4 Jan 2008 15:20:29.440 : ---> STOR rxt.ibt.ppcm.b0001.d0000001.doc.out
DEBUG [FTPControlSocket] 4 Jan 2008 15:20:29.440 : 150 File status okay; about to open data connection.
DEBUG [FTPActiveDataSocket] 4 Jan 2008 15:20:29.440 : Calling accept()
DEBUG [FTPActiveDataSocket] 4 Jan 2008 15:20:29.440 : accept() succeeded
DEBUG [FTPActiveDataSocket] 4 Jan 2008 15:20:29.440 : closeChild() succeeded
DEBUG [FTPActiveDataSocket] 4 Jan 2008 15:20:29.440 : close() succeeded
DEBUG [FTPClient] 4 Jan 2008 15:20:29.440 : Transferred 46592 bytes to remote host
DEBUG [FTPControlSocket] 4 Jan 2008 15:20:29.456 : 226 Closing data connection.
DEBUG [FTPControlSocket] 4 Jan 2008 15:20:29.456 : ListenOnAllInterfaces=true
DEBUG [FTPControlSocket] 4 Jan 2008 15:20:29.456 : ---> PORT 10,46,37,31,9,236
DEBUG [FTPControlSocket] 4 Jan 2008 15:20:29.456 : 200 PORT Command successful.
DEBUG [FTPControlSocket] 4 Jan 2008 15:20:29.456 : ---> STOR rxt.ibt.ppcm.b0001.d0000001.doc.ind
DEBUG [FTPControlSocket] 4 Jan 2008 15:20:29.456 : 150 File status okay; about to open data connection.
DEBUG [FTPActiveDataSocket] 4 Jan 2008 15:20:29.456 : Calling accept()
DEBUG [FTPActiveDataSocket] 4 Jan 2008 15:20:29.456 : accept() succeeded
DEBUG [FTPActiveDataSocket] 4 Jan 2008 15:20:29.456 : closeChild() succeeded
DEBUG [FTPActiveDataSocket] 4 Jan 2008 15:20:29.456 : close() succeeded
DEBUG [FTPClient] 4 Jan 2008 15:20:29.456 : Transferred 1148 bytes to remote host
DEBUG [FTPControlSocket] 4 Jan 2008 15:20:29.472 : 226 Closing data connection.
DEBUG [FTPControlSocket] 4 Jan 2008 15:20:29.472 : ListenOnAllInterfaces=true
DEBUG [FTPControlSocket] 4 Jan 2008 15:20:29.472 : ---> PORT 10,46,37,31,9,237
DEBUG [FTPControlSocket] 4 Jan 2008 15:20:29.487 : 200 PORT Command successful.
DEBUG [FTPControlSocket] 4 Jan 2008 15:20:29.534 : ---> STOR rxt.ibt.ppcm.b0001.d0000003.doc.out
DEBUG [FTPControlSocket] 4 Jan 2008 15:20:29.534 : 150 File status okay; about to open data connection.
DEBUG [FTPActiveDataSocket] 4 Jan 2008 15:20:29.534 : Calling accept()
DEBUG [FTPActiveDataSocket] 4 Jan 2008 15:20:29.550 : accept() succeeded
DEBUG [FTPActiveDataSocket] 4 Jan 2008 15:20:29.550 : closeChild() succeeded
DEBUG [FTPActiveDataSocket] 4 Jan 2008 15:20:29.550 : close() succeeded

Answer 1

With the FTP protocol, adding sleeps is sometimes necessary when many files are uploaded within a short period of time (because of the file descriptor problem).

And yes, FileTransferClient wraps FTPClient - it is a new, simpler to use class that we hope will make it easier for people to get started with FTP.

Answer 2

Thanks for your reply. I have configured a sleep time between uploads and it works fine.

I am all set with the issue, but it would be helpful if you could throw some light on these questions.
1. Do you recommend any specific sleep time between file uploads? and does it depend on file size? (I tested with file ranges 2KB to 128MB and 10 millis seem to work all the time for the server where it is failing)
2. Could you recommend any resource from where I could read more about file descriptors and how it is used from within EDT API?

Thanks.