问题
I'm trying to provide communication between a C# app and a Java app on windows using named pipes with the method described by v01ver in this question: How to open a Windows named pipe from Java?
I'm running into a problem on the Java side because I have a reader thread constantly waiting for input on the pipe and when I try to write to the pipe from my main thread it gets stuck forever.
final RandomAccessFile pipe;
try {
pipe = new RandomAccessFile("\\\\.\\pipe\\mypipe", "rw");
}
catch (FileNotFoundException ex) {
ex.printStackTrace();
return;
}
Thread readerThread = new Thread(new Runnable() {
@Override
public void run() {
String line = null;
try {
while (null != (line = pipe.readLine())) {
System.out.println(line);
}
}
catch (IOException ex) {
ex.printStackTrace();
}
}
});
readerThread.start();
try { Thread.sleep(500); } catch (InterruptedException e) {}
try {
System.out.println("Writing a message...");
pipe.write("Hello there.\n".getBytes());
System.out.println("Finished.");
}
catch (IOException ex) {
ex.printStackTrace();
}
The output is:
Writing a message...and then it waits forever.
How can I write to a named pipe while waiting for input in another thread?
回答1:
This is expected behaviour of pipes. It is supposed to hang untill other process connects to the pipe and reads it.
回答2:
I suppose that RandomAccessFile is not the right API here. Try a FileInputStream + FileOutputStream on the Java side. But that is only a guess, as I last used the Windows API in times when named pipes didn't yet exist.
回答3:
I have a same problem -- communication between a C#/Python app and a Java app on windows using named pipes:
We have example of Client Code written on Java, but in line String echoResponse = pipe.readLine(); tread waits forever.
try {
// Connect to the pipe
RandomAccessFile pipe = new RandomAccessFile("\\\\.\\pipe\\testpipe", "rw");
String echoText = "Hello word\n";
// write to pipe
pipe.write ( echoText.getBytes() );
// read response
String echoResponse = pipe.readLine();
System.out.println("Response: " + echoResponse );
pipe.close();
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
Solution of problem: I have a ServerPipe code written on Python from here Example Code - Named Pipes: and run its on Python 2.6.6
from ctypes import *
PIPE_ACCESS_DUPLEX = 0x3
PIPE_TYPE_MESSAGE = 0x4
PIPE_READMODE_MESSAGE = 0x2
PIPE_WAIT = 0
PIPE_UNLIMITED_INSTANCES = 255
BUFSIZE = 4096
NMPWAIT_USE_DEFAULT_WAIT = 0
INVALID_HANDLE_VALUE = -1
ERROR_PIPE_CONNECTED = 535
MESSAGE = "Default answer from server\0"
szPipename = "\\\\.\\pipe\\mynamedpipe"
def ReadWrite_ClientPipe_Thread(hPipe):
chBuf = create_string_buffer(BUFSIZE)
cbRead = c_ulong(0)
while 1:
fSuccess = windll.kernel32.ReadFile(hPipe, chBuf, BUFSIZE,
byref(cbRead), None)
if ((fSuccess ==1) or (cbRead.value != 0)):
print chBuf.value
cbWritten = c_ulong(0)
fSuccess = windll.kernel32.WriteFile(hPipe,
c_char_p(MESSAGE),
len(MESSAGE),
byref(cbWritten),
None
)
else:
break
if ( (not fSuccess) or (len(MESSAGE) != cbWritten.value)):
print "Could not reply to the client's request from the
pipe"
break
else:
print "Number of bytes written:", cbWritten.value
windll.kernel32.FlushFileBuffers(hPipe)
windll.kernel32.DisconnectNamedPipe(hPipe)
windll.kernel32.CloseHandle(hPipe)
return 0
def main():
THREADFUNC = CFUNCTYPE(c_int, c_int)
thread_func = THREADFUNC(ReadWrite_ClientPipe_Thread)
while 1:
hPipe = windll.kernel32.CreateNamedPipeA(szPipename,
PIPE_ACCESS_DUPLEX,
PIPE_TYPE_MESSAGE |
PIPE_READMODE_MESSAGE
|
PIPE_WAIT,
PIPE_UNLIMITED_INSTANCES,
BUFSIZE, BUFSIZE,
NMPWAIT_USE_DEFAULT_WAIT,
None
)
if (hPipe == INVALID_HANDLE_VALUE):
print "Error in creating Named Pipe"
return 0
fConnected = windll.kernel32.ConnectNamedPipe(hPipe, None)
if ((fConnected == 0) and (windll.kernel32.GetLastError() ==
ERROR_PIPE_CONNECTED)):
fConnected = 1
if (fConnected == 1):
dwThreadId = c_ulong(0)
hThread = windll.kernel32.CreateThread(None, 0,
thread_func, hPipe, 0, byref(dwThreadId))
if (hThread == -1):
print "Create Thread failed"
return 0
else:
windll.kernel32.CloseHandle(hThread)
else:
print "Could not connect to the Named Pipe"
windll.kernel32.CloseHandle(hPipe)
return 0
if __name__ == "__main__":
main()
After server have start you can use slightly modified version of the Java Client code:
try {
// Connect to the pipe
RandomAccessFile pipe = new RandomAccessFile("\\\\.\\pipe\\mynamedpipe", "rw");
String echoText = "Hello world\n";
// write to pipe
pipe.write(echoText.getBytes());
//String aChar;
StringBuffer fullString = new StringBuffer();
while(true){
int charCode = pipe.read();
if(charCode == 0) break;
//aChar = new Character((char)charCode).toString();
fullString.append((char)charCode);
}
System.out.println("Response: " + fullString);
pipe.close();
}
catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
It works well in NetBeans 6.9.1.
回答4:
Don't worry, using RandomAccessFile to access a named pipe is correct. A named pipe is a file system object. Under Linux/Unix it is also called "fifo". Those objects are readable just like a file. (and not the same as pipes used between processes which are abstracted by Java Pipe class).
However I see two problems with your program. I cannot test it currently as I would need your test server (feel free to publish). Your reader thread waits for answers from the other side (i.e. the server). It uses readLine(), I would use a different method (for debugging reading char by char might be the best).
With Java (without JNI) you cannot actually create a named pipe (server side). Opening a named pipe with the generic method used by RandomAccessFile you will get a byte-type stream which can be one-way or duplex.
BTW: JTDS (the free JDBC driver for SQL Server) can optionally use a named pipe to access SQL server, even over the network. And it is using exactly the RandomAccessFile method.
BTW2: there is a makepipe.exe test server on older MS SQL Server installation media, however I did not find a trusted source to get that file.
回答5:
I'm not familiar with JAVA, and my C# is pretty elementary too. However I'm had a similar problem with a multithreaded C++ client that I fixed by opening the pipe for overlapped IO. Until I did this, Windows serialized reads and writes, effectively causing an unsatisfied (blocking) ReadFile to prevent completion of a subsequent WriteFile until the read was done.
See CreateFile function
FILE_FLAG_OVERLAPPED
来源：https://stackoverflow.com/questions/4974989/concurrent-read-write-of-named-pipe-in-java-on-windows