release/src/router/libncurses/ncurses/tinfo/setbuf.c

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  28
  29 /****************************************************************************
  30  *  Author: Zeyd M. Ben-Halim <zmbenhal@netcom.com> 1992,1995               *
  31  *     and: Eric S. Raymond <esr@snark.thyrsus.com>                         *
  32  *     and: Thomas E. Dickey                        1996-on                 *
  33  *     and: Juergen Pfeifer                         2008                    *
  34  ****************************************************************************/
  35
  36 /*
  37 **      setbuf.c
  38 **
  39 **      Support for set_term(), reset_shell_mode(), reset_prog_mode().
  40 **
  41 */
  42
  43 #include <curses.priv.h>
  44
  45 MODULE_ID("$Id: setbuf.c,v 1.16 2010/08/28 21:08:31 tom Exp $")
  46
  47 /*
  48  * If the output file descriptor is connected to a tty (the typical case) it
  49  * will probably be line-buffered.  Keith Bostic pointed out that we don't want
  50  * this; it hoses people running over networks by forcing out a bunch of small
  51  * packets instead of one big one, so screen updates on ptys look jerky.
  52  * Restore block buffering to prevent this minor lossage.
  53  *
  54  * The buffer size is a compromise.  Ideally we'd like a buffer that can hold
  55  * the maximum possible update size (the whole screen plus cup commands to
  56  * change lines as it's painted).  On a 66-line xterm this can become
  57  * excessive.  So we min it with the amount of data we think we can get through
  58  * two Ethernet packets (maximum packet size - 100 for TCP/IP overhead).
  59  *
  60  * Why two ethernet packets?  It used to be one, on the theory that said
  61  * packets define the maximum size of atomic update.  But that's less than the
  62  * 2000 chars on a 25 x 80 screen, and we don't want local updates to flicker
  63  * either.  Two packet lengths will handle up to a 35 x 80 screen.
  64  *
  65  * The magic '6' is the estimated length of the end-of-line cup sequence to go
  66  * to the next line.  It's generous.  We used to mess with the buffering in
  67  * init_mvcur() after cost computation, but that lost the sequences emitted by
  68  * init_acs() in setupscreen().
  69  *
  70  * "The setvbuf function may be used only after the stream pointed to by stream
  71  * has been associated with an open file and before any other operation is
  72  * performed on the stream." (ISO 7.9.5.6.)
  73  *
  74  * Grrrr...
  75  *
  76  * On a lighter note, many implementations do in fact allow an application to
  77  * reset the buffering after it has been written to.  We try to do this because
  78  * otherwise we leave stdout in buffered mode after endwin() is called.  (This
  79  * also happens with SVr4 curses).
  80  *
  81  * There are pros/cons:
  82  *
  83  * con:
  84  *      There is no guarantee that we can reestablish buffering once we've
  85  *      dropped it.
  86  *
  87  *      We _may_ lose data if the implementation does not coordinate this with
  88  *      fflush.
  89  *
  90  * pro:
  91  *      An implementation is more likely to refuse to change the buffering than
  92  *      to do it in one of the ways mentioned above.
  93  *
  94  *      The alternative is to have the application try to change buffering
  95  *      itself, which is certainly no improvement.
  96  *
  97  * Just in case it does not work well on a particular system, the calls to
  98  * change buffering are all via the macro NC_BUFFERED.  Some implementations
  99  * do indeed get confused by changing setbuf on/off, and will overrun the
 100  * buffer.  So we disable this by default (there may yet be a workaround).
 101  */
 102 NCURSES_EXPORT(void)
 103 NCURSES_SP_NAME(_nc_set_buffer) (NCURSES_SP_DCLx FILE *ofp, bool buffered)
 104 {
 105     int Cols;
 106     int Lines;
 107
 108     if (0 == SP_PARM)
 109         return;
 110
 111     Cols = *(ptrCols(SP_PARM));
 112     Lines = *(ptrLines(SP_PARM));
 113
 114     /* optional optimization hack -- do before any output to ofp */
 115 #if HAVE_SETVBUF || HAVE_SETBUFFER
 116     if (SP_PARM->_buffered != buffered) {
 117         unsigned buf_len;
 118         char *buf_ptr;
 119
 120         if (getenv("NCURSES_NO_SETBUF") != 0)
 121             return;
 122
 123         fflush(ofp);
 124 #ifdef __DJGPP__
 125         setmode(ofp, O_BINARY);
 126 #endif
 127         if (buffered != 0) {
 128             buf_len = (unsigned) min(Lines * (Cols + 6), 2800);
 129             if ((buf_ptr = SP_PARM->_setbuf) == 0) {
 130                 if ((buf_ptr = typeMalloc(char, buf_len)) == NULL)
 131                       return;
 132                 SP_PARM->_setbuf = buf_ptr;
 133                 /* Don't try to free this! */
 134             }
 135 #if !USE_SETBUF_0
 136             else
 137                 return;
 138 #endif
 139         } else {
 140 #if !USE_SETBUF_0
 141             return;
 142 #else
 143             buf_len = 0;
 144             buf_ptr = 0;
 145 #endif
 146         }
 147
 148 #if HAVE_SETVBUF
 149 #ifdef SETVBUF_REVERSED         /* pre-svr3? */
 150         (void) setvbuf(ofp, buf_ptr, buf_len, buf_len ? _IOFBF : _IOLBF);
 151 #else
 152         (void) setvbuf(ofp, buf_ptr, buf_len ? _IOFBF : _IOLBF, buf_len);
 153 #endif
 154 #elif HAVE_SETBUFFER
 155         (void) setbuffer(ofp, buf_ptr, (int) buf_len);
 156 #endif
 157
 158         SP_PARM->_buffered = buffered;
 159     }
 160 #endif /* HAVE_SETVBUF || HAVE_SETBUFFER */
 161 }
 162
 163 #if NCURSES_SP_FUNCS
 164 NCURSES_EXPORT(void)
 165 _nc_set_buffer(FILE *ofp, bool buffered)
 166 {
 167     NCURSES_SP_NAME(_nc_set_buffer) (CURRENT_SCREEN, ofp, buffered);
 168 }
 169 #endif