[NET-348] Queue is full TelnetInputStream

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 1.4, 2.2
• Fix Version/s: 3.0
• Component/s: Telnet

Environment

Windows XP, Java JRE 1.6

• Assignee: Unassigned
• Reporter: Krishnan Sivaramakrishna Iyer
• Created: 29/Dec/10 20:29
• Updated: 04/Jun/11 19:26
• Resolved: 03/Mar/11 13:47

Description

Hello

I am using Telnet library of common.net. And I got an exception

in TelnetInputStream once in a while.

The exception message was as following.

------------------------------------------------------------------------
--------------------------------------------

Exception in thread "Thread-9399" java.lang.IllegalStateException: Queue
is full! Cannot process another character.

at
org.apache.commons.net.telnet.TelnetInputStream.__processChar(TelnetInpu
tStream.java:306)

at
org.apache.commons.net.telnet.TelnetInputStream.run(TelnetInputStream.ja
va:596)

at java.lang.Thread.run(Thread.java:619)

------------------------------------------------------------------------
--------------------------------------------

At first, I think it is possible that I didn't call read() in time to
read the data in TelnetInputStream so that the buffer

of TelnetInputStream overflowed. But then I wrote a simple program to
test it and I found that it is not the cause.

Then I studied the source of TelnetInputStream. The segment of function
__processChar is as following.

280
<http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet
InputStream.html#280> private void __processChar(int ch) throws
InterruptedException
281
<http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet
InputStream.html#281> {
282
<http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet
InputStream.html#282> // Critical section because we're
altering __bytesAvailable,
283
<http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet
InputStream.html#283> // __queueTail, and the contents of
_queue.
284
<http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet
InputStream.html#284> synchronized (__queue)
285
<http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet
InputStream.html#285> {
286
<http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet
InputStream.html#286> while (__bytesAvailable >=
__queue.length - 1)
287
<http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet
InputStream.html#287> {
288
<http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet
InputStream.html#288> // The queue is full. We need to
wait before adding any more data to it. Hopefully the stream owner
289
<http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet
InputStream.html#289> // will consume some data soon!
290
<http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet
InputStream.html#290> if(__threaded)
291
<http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet
InputStream.html#291> {
292
<http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet
InputStream.html#292> __queue.notify();
293
<http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet
InputStream.html#293> try
294
<http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet
InputStream.html#294>

{ 295 <http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet InputStream.html#295> __queue.wait(); 296 <http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet InputStream.html#296> }

297
<http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet
InputStream.html#297> catch (InterruptedException
e)
298
<http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet
InputStream.html#298>

{ 299 <http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet InputStream.html#299> throw e; 300 <http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet InputStream.html#300> }

301
<http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet
InputStream.html#301> }
302
<http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet
InputStream.html#302> else
303
<http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet
InputStream.html#303>

{ 304 <http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet InputStream.html#304> // We've been asked to add another character to the queue, but it is already full and there's 305 <http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet InputStream.html#305> // no other thread to drain it. This should not have happened! 306 <http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet InputStream.html#306> throw new IllegalStateException("Queue is full! Cannot process another character."); 307 <http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet InputStream.html#307> }

308
<http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet
InputStream.html#308> }
309
<http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet
InputStream.html#309>
310
<http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet
InputStream.html#310> // Need to do this in case we're not
full, but block on a read
311
<http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet
InputStream.html#311> if (__readIsWaiting && __threaded)
312
<http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet
InputStream.html#312>

{ 313 <http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet InputStream.html#313> __queue.notify(); 314 <http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet InputStream.html#314> }

315
<http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet
InputStream.html#315>
316
<http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet
InputStream.html#316> __queue[__queueTail] = ch;
317
<http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet
InputStream.html#317> ++__bytesAvailable;
318
<http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet
InputStream.html#318>
319
<http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet
InputStream.html#319> if (++__queueTail >= __queue.length)
320
<http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet
InputStream.html#320> __queueTail = 0;
321
<http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet
InputStream.html#321> }
322
<http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet
InputStream.html#322> }

In line 306 the exception IllegalStateException is thrown. In this
condition, the variable __threaded should be false.

But I didn't call TelnetClient.setReaderThread
<http://commons.apache.org/net/api/org/apache/commons/net/telnet/TelnetC
lient.html#setReaderThread%28boolean%29> to set it to false.

The __threaded is set to true in _start() of TelnetInputStream

84
<http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet
InputStream.html#84> void _start()
85
<http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet
InputStream.html#85>

{ 86 <http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet InputStream.html#86> if(__thread == null) 87 <http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet InputStream.html#87> return; 88 <http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet InputStream.html#88> 89 <http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet InputStream.html#89> int priority; 90 <http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet InputStream.html#90> __isClosed = false; 91 <http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet InputStream.html#91> // TODO remove this 92 <http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet InputStream.html#92> // Need to set a higher priority in case JVM does not use pre-emptive 93 <http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet InputStream.html#93> // threads. This should prevent scheduler induced deadlock (rather than 94 <http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet InputStream.html#94> // deadlock caused by a bug in this code). 95 <http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet InputStream.html#95> priority = Thread.currentThread().getPriority() + 1; 96 <http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet InputStream.html#96> if (priority > Thread.MAX_PRIORITY) 97 <http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet InputStream.html#97> priority = Thread.MAX_PRIORITY; 98 <http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet InputStream.html#98> __thread.setPriority(priority); 99 <http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet InputStream.html#99> __thread.setDaemon(true); 100 <http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet InputStream.html#100> __thread.start(); 101 <http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet InputStream.html#101> __threaded = true; 102 <http://commons.apache.org/net/xref/org/apache/commons/net/telnet/Telnet InputStream.html#102> }

I guess that is there a possibility that the thread in __thread.start()
is started so fast that when __processChar() is called, the __threaded
has not been set to true.
So the exception IllegalStateException is thrown.
I think line 101 should be moved up of line 100.