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1.1 root 1: /*
2: * Copyright (c) 1983 Regents of the University of California.
3: * All rights reserved.
4: *
5: * Redistribution and use in source and binary forms are permitted
6: * provided that the above copyright notice and this paragraph are
7: * duplicated in all such forms and that any documentation,
8: * advertising materials, and other materials related to such
9: * distribution and use acknowledge that the software was developed
10: * by the University of California, Berkeley. The name of the
11: * University may not be used to endorse or promote products derived
12: * from this software without specific prior written permission.
13: * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR
14: * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED
15: * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE.
16: *
17: * @(#)README 3.11 (Berkeley) 7/9/88
18: */
19:
20: Compilation notes:
21:
22: There is only one compiler option:
23:
24: vax use Vax byte order (found in ww.h)
25: Actually MIPSEL is also little-endian.
26: Anyway, they should already be defined in the
27: preprocessor.
28: If neither is defined, big-endian is assumed.
29:
30: Ok, there's another one, STR_DEBUG. It turns on consistency checks
31: in the string allocator. It's been left on since performace doesn't
32: seem to suffer. There's an abort() somewhere when an inconsistency
33: is found. It hasn't happened in years.
34:
35: The file local.h contains locally tunable constants.
36:
37: The makefile used to be updated with mkmf; it has been changed
38: at various times to use cpp -M and, currently, mkdep. The only library
39: it needs is termcap.
40:
41: Window, as is, only runs on 4.3 machines.
42:
43: On 4.2 machines, at least these modifications must be done:
44:
45: delete uses of window size ioctls: TIOCGWINSZ, TIOCSWINSZ,
46: struct winsize
47: add to ww.h
48: typedef int fd_set;
49: #define FD_ZERO(s) (*(s) = 0)
50: #define FD_SET(b, s) (*(s) |= 1 << (b))
51: #define FD_ISSET(b, s) (*(s) & 1 << (b))
52: add to ww.h
53: #define sigmask(s) (1 << (s) - 1)
54:
55:
56: A few notes about the internals:
57:
58: The window package. Windows are opened by calling wwopen().
59: Wwwrite() is the primitive for writing to windows. Wwputc(), wwputs(),
60: and wwprintf() are also supported. Some of the outputs to windows are
61: delayed. Wwupdate() updates the terminal to match the internal screen
62: buffer. Wwspawn() spawns a child process on the other end of a window,
63: with its environment tailored to the window. Visible windows are
64: doubly linked in the order of their overlap. Wwadd() inserts a window
65: into the list at a given place. Wwdelete() deletes it. Windows not in
66: the list are not visible, though wwwrite() still works. Window was
67: written before the days of X and Sunview, so some of the terminology
68: is not standard.
69:
70: Most functions return -1 on error. Wwopen() returns the null
71: pointer. An error number is saved in wwerrno. Wwerror() returns an
72: error string based on wwerrno suitable for printing.
73:
74: The terminal drivers perform all output to the physical terminal,
75: including special functions like character and line insertion and
76: deletion. The window package keeps a list of known terminals. At
77: initialization time, the terminal type is matched against the list to
78: find the right terminal driver to use. The last driver, the generic
79: driver, matches all terminals and uses the termcap database. The
80: interface between the window package the terminal driver is the `tt'
81: structure. It contains pointers to functions to perform special
82: functions and terminal output, as well as flags about the
83: characteristics of the terminal. Most of these ideas are borrowed
84: from the Maryland window package, which in turn is based on Goslin's
85: Emacs.
86:
87: The IO system is semi-synchronous. Terminal input is signal
88: driven, and everything else is done synchronously with a single
89: select(). It is roughly event-driven, though not in a clean way.
90:
91: Normally, in both conversation mode and command mode, window
92: sleeps in a select() in wwiomux() waiting for data from the
93: pseudo-terminals. At the same time, terminal input causes SIGIO which
94: is caught by wwrint(). The select() returns when at least one of the
95: pseudo-terminals becomes ready for reading.
96:
97: Wwrint() is the interrupt handler for tty input. It reads input
98: into a linear buffer accessed through four pointers:
99:
100: +-------+--------------+----------------+
101: | empty | data | empty |
102: +-------+--------------+----------------+
103: ^ ^ ^ ^
104: | | | |
105: wwib wwibp wwibq wwibe
106:
107: Wwrint() appends characters at the end and increments wwibq (*wwibq++
108: = c), and characters are taken off the buffer at wwibp using the
109: wwgetc() and wwpeekc() macros. As is the convention in C, wwibq
110: and wwibe point to one position beyond the end. In addition,
111: wwrint() will do a longjmp(wwjmpbuf) if wwsetjmp is true. This is
112: used by wwiomux() to interrupt the select() which would otherwise
113: resume after the interrupt. (Actually, I hear this is not true,
114: but the longjmp feature is used to avoid a race condition as well.
115: Anyway, it means I didn't have to depend on a feature in a
116: daily-changing kernel, but that's another story.) The macro
117: wwinterrupt() returns true if the input buffer is non-empty.
118: Wwupdate(), wwwrite(), and wwiomux() check this condition and will
119: return at the first convenient opportunity when it becomes true.
120: In the case of wwwrite(), the flag ww_nointr in the window structure
121: overrides this. This feature allows the user to interrupt lengthy
122: outputs safely. The structure of the input buffer is designed to
123: avoid race conditions without blocking interrupts.
124:
125: Actually, wwsetjmp and wwinterrupt() are part of a software
126: interrupt scheme used by the two interrupt catchers wwrint() and
127: wwchild(). Asserting the interrupt lets the synchronous parts of
128: the program know that there's an interesting asynchronous condition
129: (i.e., got a keyboard character, or a child process died) that they
130: might want to process before anything else. The synchronous routines
131: can check for this condition with wwinterrupt() or by arranging
132: that a longjmp() be done.
133:
134: Wwiomux() copies pseudo-terminal output into their corresponding
135: windows. Without anything to do, it blocks in a select(), waiting for
136: read ready on pseudo-terminals. Reads are done into per-window buffers
137: in the window structures. When there is at least one buffer non-empty,
138: wwiomux() finds the top most of these windows and writes it using
139: wwwrite(). Then the process is repeated. A non-blocking select() is
140: done after a wwwrite() to pick up any output that may have come in
141: during the write, which may take a long time. Specifically, we use
142: this to stop output or flush buffer when a pseudo-terminal tells us to
143: (we use pty packet mode). The select() blocks only when all of the
144: windows' buffers are empty. A wwupdate() is done prior to this, which
145: is the only time the screen is guaranteed to be completely up to date.
146: Wwiomux() loops until wwinterrupt() becomes true.
147:
148: The top level routine for all this is mloop(). In conversation
149: mode, it simply calls wwiomux(), which only returns when input is
150: available. The input buffer is then written to the pseudo-terminal of
151: the current window. If the escape character is found in the input,
152: command mode is entered. Otherwise, the process is repeated. In
153: command mode, control is transferred to docmd() which returns only when
154: conversation mode is reentered. Docmd() and other command processing
155: routines typically wait for input in a loop:
156:
157: while (wwpeekc() < 0)
158: wwiomux();
159:
160: When the loop terminates, wwgetc() is used to read the input buffer.
161:
162: Output to the physical terminal is handled by the lowest level
163: routines of the window package, in the files ttoutput.c and tt.h. The
164: standard IO package is not used, to get better control over buffering
165: and to use non-blocking reads in wwrint(). The buffer size is set to
166: approximately one second of output time, based on the baudrate.
167:
168: The result of all this complexity is faster response time,
169: especially in output stopping and flushing. Wwwrite() checks
170: wwinterrupt() after every line. It also calls wwupdate() for each line
171: it writes. The output buffer is limited to one second of output time.
172: Thus, there is usually only a delay of one to two lines plus one second
173: after a ^C or ^S. Also, commands that produce lengthy output can be
174: aborted without actually showing all of it on the terminal. (Try the
175: '?' command followed by escape immediately.)
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