GRASS GIS 8 Programmer's Manual  8.4.0dev(2024)-55b2a2bccc
pagein.c
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1 /**
2  * \file pagein.c
3  *
4  * \brief Segment page-in routines.
5  *
6  * This program is free software under the GNU General Public License
7  * (>=v2). Read the file COPYING that comes with GRASS for details.
8  *
9  * \author GRASS GIS Development Team
10  *
11  * \date 2005-2009
12  */
13 
14 #include <stdio.h>
15 #include <unistd.h>
16 #include <string.h>
17 #include <errno.h>
18 #include <grass/gis.h>
19 #include "local_proto.h"
20 
21 /**
22  * \brief Internal use only
23  *
24  * Segment pagein.
25  *
26  * Finds <b>n</b> in the segment file, <b>seg</b>, and selects it as the
27  * current segment.
28  *
29  * \param[in] SEG segment
30  * \param[in] n segment number
31  * \return 1 if successful
32  * \return -1 if unable to seek or read segment file
33  */
34 
35 int seg_pagein(SEGMENT *SEG, int n)
36 {
37  int cur;
38  int read_result;
39 
40  /* is n the current segment? */
41  if (n == SEG->scb[SEG->cur].n)
42  return SEG->cur;
43 
44  /* segment n is in memory ? */
45 
46  if (SEG->load_idx[n] >= 0) {
47  cur = SEG->load_idx[n];
48 
49  if (SEG->scb[cur].age != SEG->youngest) {
50  /* splice out */
51  SEG->scb[cur].age->younger->older = SEG->scb[cur].age->older;
52  SEG->scb[cur].age->older->younger = SEG->scb[cur].age->younger;
53  /* splice in */
54  SEG->scb[cur].age->younger = SEG->youngest->younger;
55  SEG->scb[cur].age->older = SEG->youngest;
56  SEG->scb[cur].age->older->younger = SEG->scb[cur].age;
57  SEG->scb[cur].age->younger->older = SEG->scb[cur].age;
58  /* make it youngest */
59  SEG->youngest = SEG->scb[cur].age;
60  }
61 
62  return SEG->cur = cur;
63  }
64 
65  /* find a slot to use to hold segment */
66  if (!SEG->nfreeslots) {
67  /* use oldest segment */
68  SEG->oldest = SEG->oldest->younger;
69  cur = SEG->oldest->cur;
70  SEG->oldest->cur = -1;
71 
72  /* unload segment */
73  if (SEG->scb[cur].n >= 0) {
74  SEG->load_idx[SEG->scb[cur].n] = -1;
75 
76  /* write it out if dirty */
77  if (SEG->scb[cur].dirty) {
78  if (seg_pageout(SEG, cur) < 0)
79  return -1;
80  }
81  }
82  }
83  else {
84  /* free slots left */
85  cur = SEG->freeslot[--SEG->nfreeslots];
86  }
87 
88  /* read in the segment */
89  SEG->scb[cur].n = n;
90  SEG->scb[cur].dirty = 0;
91  SEG->seek(SEG, SEG->scb[cur].n, 0);
92 
93  read_result = read(SEG->fd, SEG->scb[cur].buf, SEG->size);
94 
95  if (read_result == 0) {
96  /* this can happen if the file was not zero-filled,
97  * i.e. formatted with Segment_format_nofill() or
98  * Segment_format() used lseek for file initialization */
99  G_debug(1, "Segment pagein: zero read");
100  memset(SEG->scb[cur].buf, 0, SEG->size);
101  }
102  else if (read_result != SEG->size) {
103  G_debug(2, "Segment pagein: read_result=%d SEG->size=%d", read_result,
104  SEG->size);
105 
106  if (read_result < 0)
107  G_warning("Segment pagein: %s", strerror(errno));
108  else
109  G_warning("Segment pagein: short count during read(), got %d, "
110  "expected %d",
111  read_result, SEG->size);
112 
113  return -1;
114  }
115 
116  /* add loaded segment to index */
117  SEG->load_idx[n] = cur;
118 
119  /* make it youngest segment */
120  SEG->youngest = SEG->youngest->younger;
121  SEG->scb[cur].age = SEG->youngest;
122  SEG->youngest->cur = cur;
123 
124  return SEG->cur = cur;
125 }
void G_warning(const char *,...) __attribute__((format(printf
int G_debug(int, const char *,...) __attribute__((format(printf
int seg_pagein(SEGMENT *SEG, int n)
Internal use only.
Definition: pagein.c:35
int seg_pageout(SEGMENT *SEG, int i)
Internal use only.
Definition: pageout.c:35
struct aq * age
Definition: segment.h:48
char dirty
Definition: segment.h:47
char * buf
Definition: segment.h:46
int * freeslot
Definition: segment.h:53
int cur
Definition: segment.h:58
struct aq * youngest
Definition: segment.h:55
struct aq * oldest
Definition: segment.h:56
int * load_idx
Definition: segment.h:51
int nfreeslots
Definition: segment.h:52
struct SEGMENT::scb * scb
int fd
Definition: segment.h:43
int(* seek)(const struct SEGMENT *S, int, int)
Definition: segment.h:40
int size
Definition: segment.h:27
struct aq * younger
Definition: segment.h:16
int cur
Definition: segment.h:15
struct aq * older
Definition: segment.h:16