GRASS GIS 8 Programmer's Manual 8.2.1(2023)-exported
pagein.c
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1
2/**
3 * \file pagein.c
4 *
5 * \brief Segment page-in routines.
6 *
7 * This program is free software under the GNU General Public License
8 * (>=v2). Read the file COPYING that comes with GRASS for details.
9 *
10 * \author GRASS GIS Development Team
11 *
12 * \date 2005-2009
13 */
14
15#include <stdio.h>
16#include <unistd.h>
17#include <string.h>
18#include <errno.h>
19#include <grass/gis.h>
20#include "local_proto.h"
21
22
23/**
24 * \brief Internal use only
25 *
26 * Segment pagein.
27 *
28 * Finds <b>n</b> in the segment file, <b>seg</b>, and selects it as the
29 * current segment.
30 *
31 * \param[in] SEG segment
32 * \param[in] n segment number
33 * \return 1 if successful
34 * \return -1 if unable to seek or read segment file
35 */
36
37int seg_pagein(SEGMENT * SEG, int n)
38{
39 int cur;
40 int read_result;
41
42 /* is n the current segment? */
43 if (n == SEG->scb[SEG->cur].n)
44 return SEG->cur;
45
46 /* segment n is in memory ? */
47
48 if (SEG->load_idx[n] >= 0) {
49 cur = SEG->load_idx[n];
50
51 if (SEG->scb[cur].age != SEG->youngest) {
52 /* splice out */
53 SEG->scb[cur].age->younger->older = SEG->scb[cur].age->older;
54 SEG->scb[cur].age->older->younger = SEG->scb[cur].age->younger;
55 /* splice in */
56 SEG->scb[cur].age->younger = SEG->youngest->younger;
57 SEG->scb[cur].age->older = SEG->youngest;
58 SEG->scb[cur].age->older->younger = SEG->scb[cur].age;
59 SEG->scb[cur].age->younger->older = SEG->scb[cur].age;
60 /* make it youngest */
61 SEG->youngest = SEG->scb[cur].age;
62 }
63
64 return SEG->cur = cur;
65 }
66
67 /* find a slot to use to hold segment */
68 if (!SEG->nfreeslots) {
69 /* use oldest segment */
70 SEG->oldest = SEG->oldest->younger;
71 cur = SEG->oldest->cur;
72 SEG->oldest->cur = -1;
73
74 /* unload segment */
75 if (SEG->scb[cur].n >= 0) {
76 SEG->load_idx[SEG->scb[cur].n] = -1;
77
78 /* write it out if dirty */
79 if (SEG->scb[cur].dirty) {
80 if (seg_pageout(SEG, cur) < 0)
81 return -1;
82 }
83 }
84 }
85 else {
86 /* free slots left */
87 cur = SEG->freeslot[--SEG->nfreeslots];
88 }
89
90 /* read in the segment */
91 SEG->scb[cur].n = n;
92 SEG->scb[cur].dirty = 0;
93 SEG->seek(SEG, SEG->scb[cur].n, 0);
94
95 read_result = read(SEG->fd, SEG->scb[cur].buf, SEG->size);
96
97 if (read_result == 0) {
98 /* this can happen if the file was not zero-filled,
99 * i.e. formatted with Segment_format_nofill() or
100 * Segment_format() used lseek for file initialization */
101 G_debug(1, "Segment pagein: zero read");
102 memset(SEG->scb[cur].buf, 0, SEG->size);
103 }
104 else if (read_result != SEG->size) {
105 G_debug(2, "Segment pagein: read_result=%d SEG->size=%d",
106 read_result, SEG->size);
107
108 if (read_result < 0)
109 G_warning("Segment pagein: %s", strerror(errno));
110 else
112 ("Segment pagein: short count during read(), got %d, expected %d",
113 read_result, SEG->size);
114
115 return -1;
116 }
117
118 /* add loaded segment to index */
119 SEG->load_idx[n] = cur;
120
121 /* make it youngest segment */
122 SEG->youngest = SEG->youngest->younger;
123 SEG->scb[cur].age = SEG->youngest;
124 SEG->youngest->cur = cur;
125
126 return SEG->cur = cur;
127}
int G_debug(int level, const char *msg,...)
Print debugging message.
Definition: debug.c:65
void G_warning(const char *msg,...)
Print a warning message to stderr.
Definition: gis/error.c:204
int seg_pagein(SEGMENT *SEG, int n)
Internal use only.
Definition: pagein.c:37
int seg_pageout(SEGMENT *SEG, int i)
Internal use only.
Definition: pageout.c:37