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2 * Copyright (c) 1998-2003,2007 Free Software Foundation, Inc. *
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5 * copy of this software and associated documentation files (the *
6 * "Software"), to deal in the Software without restriction, including *
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15 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS *
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27 ****************************************************************************/
29 /****************************************************************************
30 * Author: Zeyd M. Ben-Halim <zmbenhal@netcom.com> 1992,1995 *
31 * and: Eric S. Raymond <esr@snark.thyrsus.com> *
32 ****************************************************************************/
37 ** Support for set_term(), reset_shell_mode(), reset_prog_mode().
41 #include <curses.priv.h>
43 MODULE_ID("$Id: setbuf.c,v 1.13 2007/05/12 19:04:02 tom Exp $")
46 * If the output file descriptor is connected to a tty (the typical case) it
47 * will probably be line-buffered. Keith Bostic pointed out that we don't want
48 * this; it hoses people running over networks by forcing out a bunch of small
49 * packets instead of one big one, so screen updates on ptys look jerky.
50 * Restore block buffering to prevent this minor lossage.
52 * The buffer size is a compromise. Ideally we'd like a buffer that can hold
53 * the maximum possible update size (the whole screen plus cup commands to
54 * change lines as it's painted). On a 66-line xterm this can become
55 * excessive. So we min it with the amount of data we think we can get through
56 * two Ethernet packets (maximum packet size - 100 for TCP/IP overhead).
58 * Why two ethernet packets? It used to be one, on the theory that said
59 * packets define the maximum size of atomic update. But that's less than the
60 * 2000 chars on a 25 x 80 screen, and we don't want local updates to flicker
61 * either. Two packet lengths will handle up to a 35 x 80 screen.
63 * The magic '6' is the estimated length of the end-of-line cup sequence to go
64 * to the next line. It's generous. We used to mess with the buffering in
65 * init_mvcur() after cost computation, but that lost the sequences emitted by
66 * init_acs() in setupscreen().
68 * "The setvbuf function may be used only after the stream pointed to by stream
69 * has been associated with an open file and before any other operation is
70 * performed on the stream." (ISO 7.9.5.6.)
74 * On a lighter note, many implementations do in fact allow an application to
75 * reset the buffering after it has been written to. We try to do this because
76 * otherwise we leave stdout in buffered mode after endwin() is called. (This
77 * also happens with SVr4 curses).
79 * There are pros/cons:
82 * There is no guarantee that we can reestablish buffering once we've
85 * We _may_ lose data if the implementation does not coordinate this with
89 * An implementation is more likely to refuse to change the buffering than
90 * to do it in one of the ways mentioned above.
92 * The alternative is to have the application try to change buffering
93 * itself, which is certainly no improvement.
95 * Just in case it does not work well on a particular system, the calls to
96 * change buffering are all via the macro NC_BUFFERED. Some implementations
97 * do indeed get confused by changing setbuf on/off, and will overrun the
98 * buffer. So we disable this by default (there may yet be a workaround).
101 _nc_set_buffer(FILE *ofp, bool buffered)
103 /* optional optimization hack -- do before any output to ofp */
104 #if HAVE_SETVBUF || HAVE_SETBUFFER
105 if (SP->_buffered != buffered) {
109 if (getenv("NCURSES_NO_SETBUF") != 0)
114 setmode(ofp, O_BINARY);
117 buf_len = min(LINES * (COLS + 6), 2800);
118 if ((buf_ptr = SP->_setbuf) == 0) {
119 if ((buf_ptr = typeMalloc(char, buf_len)) == NULL)
121 SP->_setbuf = buf_ptr;
122 /* Don't try to free this! */
138 #ifdef SETVBUF_REVERSED /* pre-svr3? */
139 (void) setvbuf(ofp, buf_ptr, buf_len, buf_len ? _IOFBF : _IOLBF);
141 (void) setvbuf(ofp, buf_ptr, buf_len ? _IOFBF : _IOLBF, buf_len);
144 (void) setbuffer(ofp, buf_ptr, (int) buf_len);
147 SP->_buffered = buffered;
149 #endif /* HAVE_SETVBUF || HAVE_SETBUFFER */