src/common/execcmn.cpp

   1 ///////////////////////////////////////////////////////////////////////////////
   2 // Name:        common/wxexec.cpp
   3 // Purpose:     defines wxStreamTempInputBuffer which is used by Unix and MSW
   4 //              implementations of wxExecute; this file is only used by the
   5 //              library and never by the user code
   6 // Author:      Vadim Zeitlin
   7 // Modified by:
   8 // Created:     20.08.02
   9 // RCS-ID:      $Id$
  10 // Copyright:   (c) 2002 Vadim Zeitlin <vadim@wxwindows.org>
  11 // Licence:     wxWindows licence
  12 ///////////////////////////////////////////////////////////////////////////////
  13
  14 #ifndef _WX_WXEXEC_CPP_
  15 #define _WX_WXEXEC_CPP_
  16
  17 // this file should never be compiled directly, just included by other code
  18 #ifndef _WX_USED_BY_WXEXECUTE_
  19     #error "You should never directly build this file!"
  20 #endif
  21
  22 // ----------------------------------------------------------------------------
  23 // wxStreamTempInputBuffer
  24 // ----------------------------------------------------------------------------
  25
  26 /*
  27    wxStreamTempInputBuffer is a hack which we need to solve the problem of
  28    executing a child process synchronously with IO redirecting: when we do
  29    this, the child writes to a pipe we open to it but when the pipe buffer
  30    (which has finite capacity, e.g. commonly just 4Kb) becomes full we have to
  31    read data from it because the child blocks in its write() until then and if
  32    it blocks we are never going to return from wxExecute() so we dead lock.
  33
  34    So here is the fix: we now read the output as soon as it appears into a temp
  35    buffer (wxStreamTempInputBuffer object) and later just stuff it back into
  36    the stream when the process terminates. See supporting code in wxExecute()
  37    itself as well.
  38
  39    Note that this is horribly inefficient for large amounts of output (count
  40    the number of times we copy the data around) and so a better API is badly
  41    needed! However it's not easy to devise a way to do this keeping backwards
  42    compatibility with the existing wxExecute(wxEXEC_SYNC)...
  43 */
  44
  45 class wxStreamTempInputBuffer
  46 {
  47 public:
  48     wxStreamTempInputBuffer();
  49
  50     // call to associate a stream with this buffer, otherwise nothing happens
  51     // at all
  52     void Init(wxPipeInputStream *stream);
  53
  54     // check for input on our stream and cache it in our buffer if any
  55     //
  56     // return true if anything was done
  57     bool Update();
  58
  59     ~wxStreamTempInputBuffer();
  60
  61 private:
  62     // the stream we're buffering, if NULL we don't do anything at all
  63     wxPipeInputStream *m_stream;
  64
  65     // the buffer of size m_size (NULL if m_size == 0)
  66     void *m_buffer;
  67
  68     // the size of the buffer
  69     size_t m_size;
  70
  71     wxDECLARE_NO_COPY_CLASS(wxStreamTempInputBuffer);
  72 };
  73
  74 inline wxStreamTempInputBuffer::wxStreamTempInputBuffer()
  75 {
  76     m_stream = NULL;
  77     m_buffer = NULL;
  78     m_size = 0;
  79 }
  80
  81 inline void wxStreamTempInputBuffer::Init(wxPipeInputStream *stream)
  82 {
  83     m_stream = stream;
  84 }
  85
  86 inline
  87 bool wxStreamTempInputBuffer::Update()
  88 {
  89     if ( !m_stream || !m_stream->CanRead() )
  90         return false;
  91
  92     // realloc in blocks of 4Kb: this is the default (and minimal) buffer
  93     // size of the Unix pipes so it should be the optimal step
  94     //
  95     // NB: don't use "static int" in this inline function, some compilers
  96     //     (e.g. IBM xlC) don't like it
  97     enum { incSize = 4096 };
  98
  99     void *buf = realloc(m_buffer, m_size + incSize);
 100     if ( !buf )
 101     {
 102         // don't read any more, we don't have enough memory to do it
 103         m_stream = NULL;
 104     }
 105     else // got memory for the buffer
 106     {
 107         m_buffer = buf;
 108         m_stream->Read((char *)m_buffer + m_size, incSize);
 109         m_size += m_stream->LastRead();
 110     }
 111
 112     return true;
 113 }
 114
 115 inline
 116 wxStreamTempInputBuffer::~wxStreamTempInputBuffer()
 117 {
 118     if ( m_buffer )
 119     {
 120         m_stream->Ungetch(m_buffer, m_size);
 121         free(m_buffer);
 122     }
 123 }
 124
 125 #endif // _WX_WXEXEC_CPP_
 126