title: Thread safety of SocketOutputStream
body: <p>I know that thread safety of java sockets has been discussed in several threads here on stackoverflow, but I haven't been able to find a clear answer to this question - Is it, in practice, safe to have multiple threads concurrently write to the same SocketOutputStream, or is there a risk that the data sent from one thread gets mixed up with the data from another tread? (For example the receiver on the other end first receives the first half of one thread's message and then some data from another thread's message and then the rest of the first thread's message)</p>
  
  <p>The reason I said "in practice" is that I know the Socket class isn't documented as thread-safe, but if it actually is safe in current implementations, then that's good enough for me. The specific implementation I'm most curious about is Hotspot running on Linux. </p>
  
  <p>When looking at the Java layer of hotspot's implementation, more specifically the implementation of socketWrite() in SocketOutputStream, it looks like it should be thread safe as long as the native implementation of socketWrite0() is safe. However, when looking at the implemention of that method (j2se/src/solaris/native/java/net/SocketOutputStream.c), it seems to split the data to be sent into chunks of 64 or 128kb (depending on whether it's a 64bit JVM) and then sends the chunks in seperate writes. </p>
  
  <p>So - to me, it looks like sending more than 64kb from different threads is not safe, but if it's less than 64kb it should be safe... but I could very well be missing something important here. Has anyone else here looked at this and come to a different conclusion?</p>