Interprocess Communication. Topic II, Named Pipes

University:
California State University, Northridge
Course:
COMP 222 | Computer Organization
Academic year:

2024
Views:

342

Pages:

25
Author:

kidimuqyn

Chapter 11 Interprocess Communication 1 TOPIC II Named Pipes 14 NAMED PIPES (1 of 2) Good mechanism for implementing IPC-based applications, including limited networked client/server systems   Use WinSockets for serious networked IPC Use named pipes primarily for single-system IPC Message-oriented, so the reading process can read varying length messages precisely as sent by the writing process 15 NAMED PIPES (2 of 2) Bi-directional, so two processes can exchange messages over the same pipe You can create multiple, independent instances of a named pipe   Several clients can communicate with a single server using the same pipe Server can respond to a client using the same instance Pipe name can be accessed by systems on a network 16 Client 0 CLIENTS AND SERVER USING NAMED PIPES h = CreateFile (PipeName); while ( ) { WriteFile (h, &Request); ReadFile (h, &Response) /* Process Response */ } CloseHandle (h); Up to N Clients Server Pipe Instance 0 for (i = 0; i < N, i++) h [i] = CreateNamedPipe (PipeName, N); · · · · /* Poll each pipe instance, get request, return response */ i = 0; Client (N-1) h = CreateFile (PipeName); while ( ) { WriteFile (h, &Request); ReadFile (h, &Response) /* Process Response */ } CloseHandle (h); /* Create N instances */ Pipe Instance N-1 while ( ) { if PeekNamedPipe (h [i]) { ReadFile (h [i], &Request); /* Create response */ WriteFile (h [i], &Response); } i = i++ % N; } 17 USING NAMED PIPES (1 of 2) The model above has two significant shortcomings:   The server polls the named pipe handles rather than waiting for a connection or a request. This will be fixed in the next lab. It can only process one client request at a time. This will be fixed using threads in the next module. Also, a suggested extension in this module’s lab shows how to use multiple processes. 18 USING NAMED PIPES (2 of 2)    CreateNamedPipe creates the first instance of a named pipe and returns a handle The creating process is regarded as the server Client processes, possibly on other systems, open the pipe with CreateFile 19 CREATING NAMED PIPES (1 of 5) HANDLE CreateNamedPipe (LPCTSTR lpszPipeName, DWORD fdwOpenMode, DWORD fdwPipeMode, DWORD nMaxInstances, DWORD cbOutBuf, DWORD cbInBuf, DWORD dwTimeOut, LPSECURITY_ATTRIBUTES lpsa)  lpszPipeName indicates the pipe name  Must be of the form \\.\pipe\[path]pipename  You cannot create a pipe on a remote machine 20 CREATING NAMED PIPES (2 of 5) fdwOpenMode specifies one of:  PIPE_ACCESS_DUPLEX  Equivalent to GENERIC_READ | GENERIC_WRITE  PIPE_ACCESS_INBOUND — Data flow is from the client to the server only  Equivalent to GENERIC_READ  PIPE_ACCESS_OUTBOUND The mode can also specify FILE_FLAG_WRITE_THROUGH (not used with message pipes) and FILE_FLAG_OVERLAPPED 21 CREATING NAMED PIPES (3 of 5) fdwPipeMode has three mutually exclusive flag pairs indicating whether writing is message- or byte-oriented, whether reading is by messages or blocks, and whether read operations block  PIPE_TYPE_BYTE and PIPE_TYPE_MESSAGE    Mutually exclusive Writing stream of bytes or messages Use the same type value for all pipe instances 22 CREATING NAMED PIPES (4 of 5)  PIPE_READMODE_BYTE and PIPE_READMODE_MESSAGE    Reading stream of bytes or messages PIPE_READMODE_MESSAGE requires PIPE_TYPE_MESSAGE PIPE_WAIT and PIPE_NOWAIT determine whether ReadFile will block  Use PIPE_WAIT as there are better ways to achieve asynchronous I/O 23 CREATING NAMED PIPES (5 of 5) nMaxInstances — the number of pipe instances and, therefore, the number of simultaneous clients   Specify this same value for every CreateNamedPipe call for a given pipe PIPE_UNLIMITED_INSTANCES allows the OS to base the number on available system resources cbOutBuf and cbInBuf advise the OS on the required size of input and output buffers dwTimeOut — default time-out period (in milliseconds) for the WaitNamedPipe function lpsa is as in all the other “Create” functions 24 POLLING BOOL PeekNamedPipe (HANDLE hPipe, LPVOID lpvBuffer, DWORD cbBuffer, LPDWORD lpcbRead, LPDWORD lpcbAvail, LPDWORD lpcbMessage)     Nondestructively reads any bytes or messages in the pipe Does not block Returns immediately Test *lpcbAvail to determine whether there is data in the pipe 25 NAMED PIPE CLIENT CONNECTIONS A client can “connect” to a named pipe using CreateFile with the named pipe name  In many cases, the client and server are on the same machine, and the name would be of the form: \\.\pipe\[path]pipename  If the server is on a different machine, the name would be: \\servername\pipe\[path]pipename  Using the name “.” when the server is local, rather than the local machine name (this is faster) 26 NAMED PIPE STATUS FUNCTIONS (1 of 2) Two functions are provided to interrogate pipe status information   GetNamedPipeHandleState returns information, given an open handle, on whether the pipe is in blocking or nonblocking mode, whether it is message- or byte-oriented, the number of pipe instances, and so on SetNamedPipeHandleState allows you to set the same state attributes 27 NAMED PIPE STATUS FUNCTIONS (2 of 2) Another function is provided to set state information  GetNamedPipeInfo determines whether the handle is for a client or server instance, buffer sizes, and so on 28 NAMED PIPE CONVENIENCE FUNCTIONS (1 of 7) Given a “long-lived” connection, you can combine the WriteFile, ReadFile client sequence  There are also performance advantages as a connection is not required 29 NAMED PIPE CONVENIENCE FUNCTIONS (2 of 7) BOOL TransactNamedPipe (HANDLE hNamedPipe, LPVOID lpvWriteBuf, DWORD cbWriteBuf, LPVOID lpvReadBuf, DWORD cbReadBuf, LPDWORD lpcbRead, LPOVERLAPPED lpa)   Both output and input buffers are specified *lpcbRead — The message length 30 NAMED PIPE CONVENIENCE FUNCTIONS (3 of 7) BOOL CallNamedPipe (LPCTSTR lpszPipeName, LPVOID lpvWriteBuf, DWORD cbWriteBuf, LPVOID lpvReadBuf, DWORD cbReadBuf, LPDWORD lpcbRead, DWORD dwTimeOut) 31 NAMED PIPE CONVENIENCE FUNCTIONS (4 of 7) Synchronous: Create/Write/Read/Close client “shortlived” connection  Minimizes instance use but increases connection overhead Specifies time-out period for the connection, in milliseconds or one of:    NMPWAIT_NOWAIT NMPWAIT_WAIT_FOREVER NMPWAIT_USE_DEFAULT_WAIT 32 NAMED PIPE CONVENIENCE FUNCTIONS (5 of 7) BOOL WaitNamedPipe (LPCTSTR lpszPipeName, DWORD dwTimeOut) The client can wait for an instance of the named pipe to become available 33 NAMED PIPE CONVENIENCE FUNCTIONS (6 of 7) BOOL ConnectNamedPipe (HANDLE hNamedPipe, LPOVERLAPPED lpo) BOOL DisconnectNamedPipe (HANDLE hNamedPipe) With lpo set to NULL, ConnectNamedPipe will return as soon as the server has a connection from a client 34 NAMED PIPE CONVENIENCE FUNCTIONS (7 of 7)    Normal return value is TRUE Return value is FALSE if the client connected between the server’s CreateNamedPipe call and the ConnectNamedPipe call  In this case, GetLastError returns ERROR_PIPE_CONNECTED Perform ReadFile, WriteFile operations between connect and disconnect 35 NAMED PIPE SECURITY    The important security rights for named pipes are:  GENERIC_READ  GENERIC_WRITE  SYNCHRONIZE (allowing a thread to wait on the pipe) You normally get the appropriate rights depending on the access (duplex, inbound, outbound) All three require SYNCHRONIZE 36 CLIENT-SERVER NAMED PIPES USING A SHORT-LIVED CONNECTION Client Server CreateNamedPipe WaitNamedPipe ConnectNamedPipe CreateFile WriteFile ReadFile WriteFile ReadFile DisconnectNamedPipe CloseHandle 37

Interprocess Communication. Topic II, Named Pipes

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