Marcono1234 created EXEC-122:
--------------------------------
Summary: PumpStreamHandler(OutputStream) relies on stream being
thread-safe
Key: EXEC-122
URL: https://issues.apache.org/jira/browse/EXEC-122
Project: Commons Exec
Issue Type: Bug
Affects Versions: 1.4.0
Reporter: Marcono1234
h3. Description
The constructor
{{org.apache.commons.exec.PumpStreamHandler.PumpStreamHandler(OutputStream)}}
which uses the {{OutputStream}} for both 'out' and 'err' currently does not
perform any synchronization, so potentially two threads are writing at the same
time to {{OutputStream}}.
(This also applies to the other {{PumpStreamHandler}} constructor overloads in
case the user manually provides the same {{OutputStream}} instance both as
'out' and 'err').
This is error-prone because not all {{OutputStream}} implementations are
thread-safe, and the user might not be aware of this behavior.
So it would be good to either:
- Mention in the {{PumpStreamHandler(OutputStream)}} documentation (and
possibly for the other constructor overloads as well, if the same stream
instance is used), that the {{OutputStream}} has to be thread-safe
- Or, {{PumpStreamHandler}} (or {{StreamPumper}}) should perform
synchronization, for example if the same stream instance is used by wrapping it
in a custom synchronizing {{OutputStream}}
(though maybe that is not desired if the stream is already thread-safe, e.g.
{{Files.newOutputStream}})
h3. Example
Run this code snippet:
{code}
OutputStream out = new OutputStream() {
@Override
public void write(int b) throws IOException {
System.out.println(Thread.currentThread().getName());
}
};
PumpStreamHandler p = new PumpStreamHandler(out);
p.setProcessOutputStream(new ByteArrayInputStream(new byte[1]));
p.setProcessErrorStream(new ByteArrayInputStream(new byte[1]));
p.start();
Thread.sleep(1000);
{code}
You will see that it prints two different thread sames. If you place a
breakpoint at the {{println}} you will also see that no synchronization is
performed, and the calls happen concurrently.
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