Named pipe in winows, difference between FILE_FLAG_OVERLAPPED and PIPE_NOWAIT









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I am using named pipe in windows and confused about the difference between FILE_FLAG_OVERLAPPED and PIPE_NOWAIT which are parameters set in CreateNamedPipe ,I set parameters like this.



HANDLE hPipe = CreateNamedPipe(
lpszPipename, // pipe name
PIPE_ACCESS_DUPLEX | // read/write access
FILE_FLAG_OVERLAPPED, // overlapped mode
PIPE_TYPE_MESSAGE | // message-type pipe
PIPE_READMODE_MESSAGE | // message read mode
PIPE_WAIT, // blocking mode
PIPE_UNLIMITED_INSTANCES, // unlimited instances
BUFSIZE * sizeof(TCHAR), // output buffer size
BUFSIZE * sizeof(TCHAR), // input buffer size
PIPE_TIMEOUT, // client time-out
NULL); // default security attributes


the ConnectNamedPipe return immediately and I get ERROR_IO_PENDING from GetLastError.With a nonblocking-wait handle, the connect operation returns zero immediately, and the GetLastError function returns ERROR_IO_PENDING.However the MSDN tells:
With a nonblocking-wait handle, the connect operation returns zero immediately, and the GetLastError function returns ERROR_PIPE_LISTENING.
so, what does nonblocking-wait mean, PIPE_NOWAIT or FILE_FLAG_OVERLAPPED, thanks a lot!










share|improve this question























  • It seems the MSDN uses the term "nonblocking mode" when using PIPE_ NOWAIT, and the term "overlapped mode" when using FILE_FLAG_OVERLAPPED. PIPE_NOWAIT is "supported for compatibility with Microsoft LAN Manager version 2.0 and should not be used to achieve asynchronous I/O".
    – IInspectable
    2 days ago










  • Very different options. FILE_FLAG_OVERLAPPED sets up the socket so it can handle asynchronous I/O, you can call ReadFile() with an OVERLAPPED argument and handle the read completion later. Very common for pipes, unless the traffic rate is very high you want to avoid blocking a thread too much. PIPE_NOWAIT is useful for synchronous I/O, it prevents ReadFile() from blocking if there is no data yet. Repeatedly calling ReadFile() is then required, polling in common terms. Look at a library like boost::asio to take care of the plumbing.
    – Hans Passant
    2 days ago














up vote
1
down vote

favorite












I am using named pipe in windows and confused about the difference between FILE_FLAG_OVERLAPPED and PIPE_NOWAIT which are parameters set in CreateNamedPipe ,I set parameters like this.



HANDLE hPipe = CreateNamedPipe(
lpszPipename, // pipe name
PIPE_ACCESS_DUPLEX | // read/write access
FILE_FLAG_OVERLAPPED, // overlapped mode
PIPE_TYPE_MESSAGE | // message-type pipe
PIPE_READMODE_MESSAGE | // message read mode
PIPE_WAIT, // blocking mode
PIPE_UNLIMITED_INSTANCES, // unlimited instances
BUFSIZE * sizeof(TCHAR), // output buffer size
BUFSIZE * sizeof(TCHAR), // input buffer size
PIPE_TIMEOUT, // client time-out
NULL); // default security attributes


the ConnectNamedPipe return immediately and I get ERROR_IO_PENDING from GetLastError.With a nonblocking-wait handle, the connect operation returns zero immediately, and the GetLastError function returns ERROR_IO_PENDING.However the MSDN tells:
With a nonblocking-wait handle, the connect operation returns zero immediately, and the GetLastError function returns ERROR_PIPE_LISTENING.
so, what does nonblocking-wait mean, PIPE_NOWAIT or FILE_FLAG_OVERLAPPED, thanks a lot!










share|improve this question























  • It seems the MSDN uses the term "nonblocking mode" when using PIPE_ NOWAIT, and the term "overlapped mode" when using FILE_FLAG_OVERLAPPED. PIPE_NOWAIT is "supported for compatibility with Microsoft LAN Manager version 2.0 and should not be used to achieve asynchronous I/O".
    – IInspectable
    2 days ago










  • Very different options. FILE_FLAG_OVERLAPPED sets up the socket so it can handle asynchronous I/O, you can call ReadFile() with an OVERLAPPED argument and handle the read completion later. Very common for pipes, unless the traffic rate is very high you want to avoid blocking a thread too much. PIPE_NOWAIT is useful for synchronous I/O, it prevents ReadFile() from blocking if there is no data yet. Repeatedly calling ReadFile() is then required, polling in common terms. Look at a library like boost::asio to take care of the plumbing.
    – Hans Passant
    2 days ago












up vote
1
down vote

favorite









up vote
1
down vote

favorite











I am using named pipe in windows and confused about the difference between FILE_FLAG_OVERLAPPED and PIPE_NOWAIT which are parameters set in CreateNamedPipe ,I set parameters like this.



HANDLE hPipe = CreateNamedPipe(
lpszPipename, // pipe name
PIPE_ACCESS_DUPLEX | // read/write access
FILE_FLAG_OVERLAPPED, // overlapped mode
PIPE_TYPE_MESSAGE | // message-type pipe
PIPE_READMODE_MESSAGE | // message read mode
PIPE_WAIT, // blocking mode
PIPE_UNLIMITED_INSTANCES, // unlimited instances
BUFSIZE * sizeof(TCHAR), // output buffer size
BUFSIZE * sizeof(TCHAR), // input buffer size
PIPE_TIMEOUT, // client time-out
NULL); // default security attributes


the ConnectNamedPipe return immediately and I get ERROR_IO_PENDING from GetLastError.With a nonblocking-wait handle, the connect operation returns zero immediately, and the GetLastError function returns ERROR_IO_PENDING.However the MSDN tells:
With a nonblocking-wait handle, the connect operation returns zero immediately, and the GetLastError function returns ERROR_PIPE_LISTENING.
so, what does nonblocking-wait mean, PIPE_NOWAIT or FILE_FLAG_OVERLAPPED, thanks a lot!










share|improve this question















I am using named pipe in windows and confused about the difference between FILE_FLAG_OVERLAPPED and PIPE_NOWAIT which are parameters set in CreateNamedPipe ,I set parameters like this.



HANDLE hPipe = CreateNamedPipe(
lpszPipename, // pipe name
PIPE_ACCESS_DUPLEX | // read/write access
FILE_FLAG_OVERLAPPED, // overlapped mode
PIPE_TYPE_MESSAGE | // message-type pipe
PIPE_READMODE_MESSAGE | // message read mode
PIPE_WAIT, // blocking mode
PIPE_UNLIMITED_INSTANCES, // unlimited instances
BUFSIZE * sizeof(TCHAR), // output buffer size
BUFSIZE * sizeof(TCHAR), // input buffer size
PIPE_TIMEOUT, // client time-out
NULL); // default security attributes


the ConnectNamedPipe return immediately and I get ERROR_IO_PENDING from GetLastError.With a nonblocking-wait handle, the connect operation returns zero immediately, and the GetLastError function returns ERROR_IO_PENDING.However the MSDN tells:
With a nonblocking-wait handle, the connect operation returns zero immediately, and the GetLastError function returns ERROR_PIPE_LISTENING.
so, what does nonblocking-wait mean, PIPE_NOWAIT or FILE_FLAG_OVERLAPPED, thanks a lot!







winapi ipc named-pipes overlap






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edited 2 days ago









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asked 2 days ago









Gordon

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  • It seems the MSDN uses the term "nonblocking mode" when using PIPE_ NOWAIT, and the term "overlapped mode" when using FILE_FLAG_OVERLAPPED. PIPE_NOWAIT is "supported for compatibility with Microsoft LAN Manager version 2.0 and should not be used to achieve asynchronous I/O".
    – IInspectable
    2 days ago










  • Very different options. FILE_FLAG_OVERLAPPED sets up the socket so it can handle asynchronous I/O, you can call ReadFile() with an OVERLAPPED argument and handle the read completion later. Very common for pipes, unless the traffic rate is very high you want to avoid blocking a thread too much. PIPE_NOWAIT is useful for synchronous I/O, it prevents ReadFile() from blocking if there is no data yet. Repeatedly calling ReadFile() is then required, polling in common terms. Look at a library like boost::asio to take care of the plumbing.
    – Hans Passant
    2 days ago
















  • It seems the MSDN uses the term "nonblocking mode" when using PIPE_ NOWAIT, and the term "overlapped mode" when using FILE_FLAG_OVERLAPPED. PIPE_NOWAIT is "supported for compatibility with Microsoft LAN Manager version 2.0 and should not be used to achieve asynchronous I/O".
    – IInspectable
    2 days ago










  • Very different options. FILE_FLAG_OVERLAPPED sets up the socket so it can handle asynchronous I/O, you can call ReadFile() with an OVERLAPPED argument and handle the read completion later. Very common for pipes, unless the traffic rate is very high you want to avoid blocking a thread too much. PIPE_NOWAIT is useful for synchronous I/O, it prevents ReadFile() from blocking if there is no data yet. Repeatedly calling ReadFile() is then required, polling in common terms. Look at a library like boost::asio to take care of the plumbing.
    – Hans Passant
    2 days ago















It seems the MSDN uses the term "nonblocking mode" when using PIPE_ NOWAIT, and the term "overlapped mode" when using FILE_FLAG_OVERLAPPED. PIPE_NOWAIT is "supported for compatibility with Microsoft LAN Manager version 2.0 and should not be used to achieve asynchronous I/O".
– IInspectable
2 days ago




It seems the MSDN uses the term "nonblocking mode" when using PIPE_ NOWAIT, and the term "overlapped mode" when using FILE_FLAG_OVERLAPPED. PIPE_NOWAIT is "supported for compatibility with Microsoft LAN Manager version 2.0 and should not be used to achieve asynchronous I/O".
– IInspectable
2 days ago












Very different options. FILE_FLAG_OVERLAPPED sets up the socket so it can handle asynchronous I/O, you can call ReadFile() with an OVERLAPPED argument and handle the read completion later. Very common for pipes, unless the traffic rate is very high you want to avoid blocking a thread too much. PIPE_NOWAIT is useful for synchronous I/O, it prevents ReadFile() from blocking if there is no data yet. Repeatedly calling ReadFile() is then required, polling in common terms. Look at a library like boost::asio to take care of the plumbing.
– Hans Passant
2 days ago




Very different options. FILE_FLAG_OVERLAPPED sets up the socket so it can handle asynchronous I/O, you can call ReadFile() with an OVERLAPPED argument and handle the read completion later. Very common for pipes, unless the traffic rate is very high you want to avoid blocking a thread too much. PIPE_NOWAIT is useful for synchronous I/O, it prevents ReadFile() from blocking if there is no data yet. Repeatedly calling ReadFile() is then required, polling in common terms. Look at a library like boost::asio to take care of the plumbing.
– Hans Passant
2 days ago












1 Answer
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up vote
1
down vote













PIPE_NOWAIT mean that Nonblocking mode is enabled on handle. In this mode, ReadFile, WriteFile, and ConnectNamedPipe always completed immediately.



the FILE_FLAG_OVERLAPPED mean asynchronous mode is enabled on handle. If this mode is enabled, all not synchronous io [1] operations always return immediately.



so FILE_FLAG_OVERLAPPED vs PIPE_NOWAIT - this is return immediately vs completed immediately.



completed immediately (which include return immediately ) mean that io operation is already completed when api return. but visa versa not true. if operation return immediately this not mean that operation is completed already. if operation still not completed ntapi return code STATUS_PENDING. win32 api in such situations usual set last error to ERROR_IO_PENDING.



exist 3 way determinate when io operation completed in case asynchronous handle mode.



  1. bind handle to IOCP (via CreateIoCompletionPort or
    BindIoCompletionCallback or CreateThreadpoolIo). as result when
    io complete - pointer to OVERLAPPED which we pass to io call -
    will be queued back to IOCP (in case BindIoCompletionCallback or
    CreateThreadpoolIo system yourself create IOCP and listen on it
    and call our registered callback, when pointer to OVERLAPPED will
    be queued to IOCP)

  2. some win32 api such ReadFileEx or WriteFileEx and all ntapi let
    specify APC completion routine which will be called in context of
    thread, which begin io operation, when io operation is completed.
    thread must do alertable wait in this case. this wait is not
    compatible with bind handle to IOCP (we can not use APC routine in
    api call if file handle binded to IOCP - system return invalid
    parameter error)

  3. we can create event and pass it to api call (via
    OVERLAPPED::hEvent) - in this case this event will be reset by
    system when io operation begin and set to signaled state when io
    operation is completed. unlike first 2 option in this case we have
    no additional context (in face pointer to OVERLAPPED) when io
    operation is completed. usually this is worst option.

[1] exist some io operations which is always synchronous api. for example GetFileInformationByHandleEx, SetFileInformationByHandle. but almost io operations is not synchronous io. all this io operations take pointer to OVERLAPPED as parameter. so if no pointer to OVERLAPPED in api signature - this is synchronous api call. if exist - usually asynchronous (exception CancelIoEx for example where pointer to overlapped is related not to current operation but to previous io operation which we want cancel). in particular ReadFile, WriteFile, DeviceIoControl, ConnectNamedPipe( internally this is call DeviceIoControl with FSCTL_PIPE_LISTEN) ) is not synchronous io api






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    PIPE_NOWAIT mean that Nonblocking mode is enabled on handle. In this mode, ReadFile, WriteFile, and ConnectNamedPipe always completed immediately.



    the FILE_FLAG_OVERLAPPED mean asynchronous mode is enabled on handle. If this mode is enabled, all not synchronous io [1] operations always return immediately.



    so FILE_FLAG_OVERLAPPED vs PIPE_NOWAIT - this is return immediately vs completed immediately.



    completed immediately (which include return immediately ) mean that io operation is already completed when api return. but visa versa not true. if operation return immediately this not mean that operation is completed already. if operation still not completed ntapi return code STATUS_PENDING. win32 api in such situations usual set last error to ERROR_IO_PENDING.



    exist 3 way determinate when io operation completed in case asynchronous handle mode.



    1. bind handle to IOCP (via CreateIoCompletionPort or
      BindIoCompletionCallback or CreateThreadpoolIo). as result when
      io complete - pointer to OVERLAPPED which we pass to io call -
      will be queued back to IOCP (in case BindIoCompletionCallback or
      CreateThreadpoolIo system yourself create IOCP and listen on it
      and call our registered callback, when pointer to OVERLAPPED will
      be queued to IOCP)

    2. some win32 api such ReadFileEx or WriteFileEx and all ntapi let
      specify APC completion routine which will be called in context of
      thread, which begin io operation, when io operation is completed.
      thread must do alertable wait in this case. this wait is not
      compatible with bind handle to IOCP (we can not use APC routine in
      api call if file handle binded to IOCP - system return invalid
      parameter error)

    3. we can create event and pass it to api call (via
      OVERLAPPED::hEvent) - in this case this event will be reset by
      system when io operation begin and set to signaled state when io
      operation is completed. unlike first 2 option in this case we have
      no additional context (in face pointer to OVERLAPPED) when io
      operation is completed. usually this is worst option.

    [1] exist some io operations which is always synchronous api. for example GetFileInformationByHandleEx, SetFileInformationByHandle. but almost io operations is not synchronous io. all this io operations take pointer to OVERLAPPED as parameter. so if no pointer to OVERLAPPED in api signature - this is synchronous api call. if exist - usually asynchronous (exception CancelIoEx for example where pointer to overlapped is related not to current operation but to previous io operation which we want cancel). in particular ReadFile, WriteFile, DeviceIoControl, ConnectNamedPipe( internally this is call DeviceIoControl with FSCTL_PIPE_LISTEN) ) is not synchronous io api






    share|improve this answer
























      up vote
      1
      down vote













      PIPE_NOWAIT mean that Nonblocking mode is enabled on handle. In this mode, ReadFile, WriteFile, and ConnectNamedPipe always completed immediately.



      the FILE_FLAG_OVERLAPPED mean asynchronous mode is enabled on handle. If this mode is enabled, all not synchronous io [1] operations always return immediately.



      so FILE_FLAG_OVERLAPPED vs PIPE_NOWAIT - this is return immediately vs completed immediately.



      completed immediately (which include return immediately ) mean that io operation is already completed when api return. but visa versa not true. if operation return immediately this not mean that operation is completed already. if operation still not completed ntapi return code STATUS_PENDING. win32 api in such situations usual set last error to ERROR_IO_PENDING.



      exist 3 way determinate when io operation completed in case asynchronous handle mode.



      1. bind handle to IOCP (via CreateIoCompletionPort or
        BindIoCompletionCallback or CreateThreadpoolIo). as result when
        io complete - pointer to OVERLAPPED which we pass to io call -
        will be queued back to IOCP (in case BindIoCompletionCallback or
        CreateThreadpoolIo system yourself create IOCP and listen on it
        and call our registered callback, when pointer to OVERLAPPED will
        be queued to IOCP)

      2. some win32 api such ReadFileEx or WriteFileEx and all ntapi let
        specify APC completion routine which will be called in context of
        thread, which begin io operation, when io operation is completed.
        thread must do alertable wait in this case. this wait is not
        compatible with bind handle to IOCP (we can not use APC routine in
        api call if file handle binded to IOCP - system return invalid
        parameter error)

      3. we can create event and pass it to api call (via
        OVERLAPPED::hEvent) - in this case this event will be reset by
        system when io operation begin and set to signaled state when io
        operation is completed. unlike first 2 option in this case we have
        no additional context (in face pointer to OVERLAPPED) when io
        operation is completed. usually this is worst option.

      [1] exist some io operations which is always synchronous api. for example GetFileInformationByHandleEx, SetFileInformationByHandle. but almost io operations is not synchronous io. all this io operations take pointer to OVERLAPPED as parameter. so if no pointer to OVERLAPPED in api signature - this is synchronous api call. if exist - usually asynchronous (exception CancelIoEx for example where pointer to overlapped is related not to current operation but to previous io operation which we want cancel). in particular ReadFile, WriteFile, DeviceIoControl, ConnectNamedPipe( internally this is call DeviceIoControl with FSCTL_PIPE_LISTEN) ) is not synchronous io api






      share|improve this answer






















        up vote
        1
        down vote










        up vote
        1
        down vote









        PIPE_NOWAIT mean that Nonblocking mode is enabled on handle. In this mode, ReadFile, WriteFile, and ConnectNamedPipe always completed immediately.



        the FILE_FLAG_OVERLAPPED mean asynchronous mode is enabled on handle. If this mode is enabled, all not synchronous io [1] operations always return immediately.



        so FILE_FLAG_OVERLAPPED vs PIPE_NOWAIT - this is return immediately vs completed immediately.



        completed immediately (which include return immediately ) mean that io operation is already completed when api return. but visa versa not true. if operation return immediately this not mean that operation is completed already. if operation still not completed ntapi return code STATUS_PENDING. win32 api in such situations usual set last error to ERROR_IO_PENDING.



        exist 3 way determinate when io operation completed in case asynchronous handle mode.



        1. bind handle to IOCP (via CreateIoCompletionPort or
          BindIoCompletionCallback or CreateThreadpoolIo). as result when
          io complete - pointer to OVERLAPPED which we pass to io call -
          will be queued back to IOCP (in case BindIoCompletionCallback or
          CreateThreadpoolIo system yourself create IOCP and listen on it
          and call our registered callback, when pointer to OVERLAPPED will
          be queued to IOCP)

        2. some win32 api such ReadFileEx or WriteFileEx and all ntapi let
          specify APC completion routine which will be called in context of
          thread, which begin io operation, when io operation is completed.
          thread must do alertable wait in this case. this wait is not
          compatible with bind handle to IOCP (we can not use APC routine in
          api call if file handle binded to IOCP - system return invalid
          parameter error)

        3. we can create event and pass it to api call (via
          OVERLAPPED::hEvent) - in this case this event will be reset by
          system when io operation begin and set to signaled state when io
          operation is completed. unlike first 2 option in this case we have
          no additional context (in face pointer to OVERLAPPED) when io
          operation is completed. usually this is worst option.

        [1] exist some io operations which is always synchronous api. for example GetFileInformationByHandleEx, SetFileInformationByHandle. but almost io operations is not synchronous io. all this io operations take pointer to OVERLAPPED as parameter. so if no pointer to OVERLAPPED in api signature - this is synchronous api call. if exist - usually asynchronous (exception CancelIoEx for example where pointer to overlapped is related not to current operation but to previous io operation which we want cancel). in particular ReadFile, WriteFile, DeviceIoControl, ConnectNamedPipe( internally this is call DeviceIoControl with FSCTL_PIPE_LISTEN) ) is not synchronous io api






        share|improve this answer












        PIPE_NOWAIT mean that Nonblocking mode is enabled on handle. In this mode, ReadFile, WriteFile, and ConnectNamedPipe always completed immediately.



        the FILE_FLAG_OVERLAPPED mean asynchronous mode is enabled on handle. If this mode is enabled, all not synchronous io [1] operations always return immediately.



        so FILE_FLAG_OVERLAPPED vs PIPE_NOWAIT - this is return immediately vs completed immediately.



        completed immediately (which include return immediately ) mean that io operation is already completed when api return. but visa versa not true. if operation return immediately this not mean that operation is completed already. if operation still not completed ntapi return code STATUS_PENDING. win32 api in such situations usual set last error to ERROR_IO_PENDING.



        exist 3 way determinate when io operation completed in case asynchronous handle mode.



        1. bind handle to IOCP (via CreateIoCompletionPort or
          BindIoCompletionCallback or CreateThreadpoolIo). as result when
          io complete - pointer to OVERLAPPED which we pass to io call -
          will be queued back to IOCP (in case BindIoCompletionCallback or
          CreateThreadpoolIo system yourself create IOCP and listen on it
          and call our registered callback, when pointer to OVERLAPPED will
          be queued to IOCP)

        2. some win32 api such ReadFileEx or WriteFileEx and all ntapi let
          specify APC completion routine which will be called in context of
          thread, which begin io operation, when io operation is completed.
          thread must do alertable wait in this case. this wait is not
          compatible with bind handle to IOCP (we can not use APC routine in
          api call if file handle binded to IOCP - system return invalid
          parameter error)

        3. we can create event and pass it to api call (via
          OVERLAPPED::hEvent) - in this case this event will be reset by
          system when io operation begin and set to signaled state when io
          operation is completed. unlike first 2 option in this case we have
          no additional context (in face pointer to OVERLAPPED) when io
          operation is completed. usually this is worst option.

        [1] exist some io operations which is always synchronous api. for example GetFileInformationByHandleEx, SetFileInformationByHandle. but almost io operations is not synchronous io. all this io operations take pointer to OVERLAPPED as parameter. so if no pointer to OVERLAPPED in api signature - this is synchronous api call. if exist - usually asynchronous (exception CancelIoEx for example where pointer to overlapped is related not to current operation but to previous io operation which we want cancel). in particular ReadFile, WriteFile, DeviceIoControl, ConnectNamedPipe( internally this is call DeviceIoControl with FSCTL_PIPE_LISTEN) ) is not synchronous io api







        share|improve this answer












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