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httpdirfs/src/cache.c

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#include "cache.h"
#include <sys/stat.h>
#include <sys/types.h>
#include <dirent.h>
#include <errno.h>
#include <fcntl.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>
/**
* \brief Data file block size
* \details We set it to 1024*1024*8 = 8MiB
*/
#define DEFAULT_DATA_BLK_SZ 8*1024*1024
/**
* \brief Maximum segment block count
* \details This is set to 128*1024 blocks, which uses 128KB. By default,
* this allows the user to store (128*1024)*(8*1024*1024) = 1TB of data
*/
#define DEFAULT_MAX_SEGBC 128*1024
/**
* \brief error associated with metadata
*/
typedef enum {
SUCCESS = 0, /**< Metadata read successful */
EFREAD = -1, /**< Fread failed */
EINCONSIST = -2, /**< Inconsistency in metadata */
EZERO = -3, /**< Unexpected zeros in metadata */
EMEM = -4 /**< Memory allocation failure */
} MetaError;
/* ---------------- External variables -----------------------*/
int CACHE_SYSTEM_INIT = 0;
int DATA_BLK_SZ = 0;
int MAX_SEGBC = DEFAULT_MAX_SEGBC;
/* ----------------- Static variables ----------------------- */
/**
* \brief Cache file locking
* \details Ensure cache opening and cache closing is an atomic operation
*/
static pthread_mutex_t cf_lock;
/**
* \brief The metadata directory
*/
static char *META_DIR;
/**
* \brief The data directory
*/
static char *DATA_DIR;
/**
* \brief Calculate cache system directory
*/
static char *CacheSystem_calc_dir(const char *url)
{
char *xdg_cache_home = getenv("XDG_CACHE_HOME");
if (!xdg_cache_home) {
char *home = getenv("HOME");
char *xdg_cache_home_default = "/.cache";
xdg_cache_home = path_append(home, xdg_cache_home_default);
}
if (mkdir(xdg_cache_home, S_IRWXU | S_IRWXG | S_IROTH | S_IXOTH)
&& (errno != EEXIST)) {
fprintf(stderr, "CacheSystem_calc_dir(): mkdir(): %s\n",
strerror(errno));
}
char *cache_dir_root = path_append(xdg_cache_home, "/httpdirfs/");
if (mkdir(cache_dir_root, S_IRWXU | S_IRWXG | S_IROTH | S_IXOTH)
&& (errno != EEXIST)) {
fprintf(stderr, "CacheSystem_calc_dir(): mkdir(): %s\n",
strerror(errno));
}
char *fn = path_append(cache_dir_root, "/CACHEDIR.TAG");
FILE *fp = fopen(fn, "w");
if (fn) {
fprintf(fp,
"Signature: 8a477f597d28d172789f06886806bc55\n\
# This file is a cache directory tag created by httpdirfs.\n\
# For information about cache directory tags, see:\n\
# http://www.brynosaurus.com/cachedir/\n");
} else {
fprintf(stderr, "CacheSystem_calc_dir(): fopen(%s): %s", fn,
strerror(errno));
}
if (ferror(fp)) {
fprintf(stderr,
"CacheSystem_calc_dir(): fwrite(): encountered error!\n");
}
if (fclose(fp)) {
fprintf(stderr, "CacheSystem_calc_dir(): fclose(%s): %s\n", fn,
strerror(errno));
}
CURL* c = curl_easy_init();
char *escaped_url = curl_easy_escape(c, url, 0);
char *full_path = path_append(cache_dir_root, escaped_url);
if (mkdir(full_path, S_IRWXU | S_IRWXG | S_IROTH | S_IXOTH)
&& (errno != EEXIST)) {
fprintf(stderr, "CacheSystem_calc_dir(): mkdir(): %s\n",
strerror(errno));
}
free(cache_dir_root);
curl_free(escaped_url);
curl_easy_cleanup(c);
return full_path;
}
void CacheSystem_init(const char *path, int url_supplied)
{
if (pthread_mutex_init(&cf_lock, NULL) != 0) {
fprintf(stderr,
"CacheSystem_init(): cf_lock initialisation failed!\n");
exit(EXIT_FAILURE);
}
if (url_supplied) {
path = CacheSystem_calc_dir(path);
}
fprintf(stderr, "CacheSystem_init(): directory: %s\n", path);
DIR* dir;
dir = opendir(path);
if (!dir) {
fprintf(stderr,
"CacheSystem_init(): opendir(): %s\n", strerror(errno));
exit(EXIT_FAILURE);
}
/* Handle the case of missing '/' */
if (path[strnlen(path, MAX_PATH_LEN) - 1] == '/') {
META_DIR = path_append(path, "meta/");
DATA_DIR = path_append(path, "data/");
} else {
META_DIR = path_append(path, "/meta/");
DATA_DIR = path_append(path, "/data/");
}
/* Check if directories exist, if not, create them */
if (mkdir(META_DIR, S_IRWXU | S_IRWXG | S_IROTH | S_IXOTH)
&& (errno != EEXIST)) {
fprintf(stderr, "CacheSystem_init(): mkdir(): %s\n",
strerror(errno));
}
if (mkdir(DATA_DIR, S_IRWXU | S_IRWXG | S_IROTH | S_IXOTH)
&& (errno != EEXIST)) {
fprintf(stderr, "CacheSystem_init(): mkdir(): %s\n",
strerror(errno));
}
if (!DATA_BLK_SZ) {
DATA_BLK_SZ = DEFAULT_DATA_BLK_SZ;
}
CACHE_SYSTEM_INIT = 1;
}
/**
* \brief read a metadata file
* \return
* - -1 on fread error,
* - -2 on metadata internal inconsistency
* - 0 on success
*/
static int Meta_read(Cache *cf)
{
FILE *fp = cf->mfp;
rewind(fp);
int nmemb = 0;
if (!fp) {
/* The metadata file does not exist */
fprintf(stderr, "Meta_read(): fopen(): %s\n", strerror(errno));
return EFREAD;
}
fread(&cf->time, sizeof(long), 1, fp);
fread(&cf->content_length, sizeof(off_t), 1, fp);
fread(&cf->blksz, sizeof(int), 1, fp);
fread(&cf->segbc, sizeof(long), 1, fp);
/* Error checking for fread */
if (ferror(fp)) {
fprintf(stderr,
"Meta_read(): error reading core metadata!\n");
}
/* These things really should not be zero!!! */
if (!cf->content_length || !cf->blksz || !cf->segbc) {
fprintf(stderr,
"Meta_read(): corrupt metadata: %s, content_length: %ld, \
blksz: %d, segbc: %ld\n", cf->path, cf->content_length, cf->blksz, cf->segbc);
return EZERO;
}
if (cf->blksz != DATA_BLK_SZ) {
fprintf(stderr, "Meta_read(): Warning: cf->blksz != DATA_BLK_SZ\n");
}
/* Allocate some memory for the segment */
if (cf->segbc > MAX_SEGBC) {
fprintf(stderr, "Meta_read(): Error: segbc: %ld\n", cf->segbc);
return EMEM;
}
cf->seg = calloc(cf->segbc, sizeof(Seg));
if (!cf->seg) {
fprintf(stderr, "Meta_read(): calloc failure: %s\n", strerror(errno));
return EMEM;
}
/* Read all the segment */
nmemb = fread(cf->seg, sizeof(Seg), cf->segbc, fp);
/* We shouldn't have gone past the end of the file */
if (feof(fp)) {
/* reached EOF */
fprintf(stderr,
"Meta_read(): attempted to read past the end of the file!\n");
return EINCONSIST;
}
/* Error checking for fread */
if (ferror(fp)) {
fprintf(stderr,
"Meta_read(): error reading bitmap!\n");
return EFREAD;
}
/* Check for inconsistent metadata file */
if (nmemb != cf-> segbc) {
fprintf(stderr,
"Meta_read(): corrupted metadata!\n");
return EINCONSIST;
}
return 0;
}
/**
* \brief write a metadata file
* \return
* - -1 on error,
* - 0 on success
*/
static int Meta_write(Cache *cf)
{
FILE *fp = cf->mfp;
rewind(fp);
if (!fp) {
/* Cannot create the metadata file */
fprintf(stderr, "Meta_write(): fopen(): %s\n", strerror(errno));
return -1;
}
/* These things really should not be zero!!! */
if (!cf->content_length || !cf->blksz || !cf->segbc) {
fprintf(stderr,
"Meta_write(): Warning: content_length: %ld, blksz: %d, segbc: \
%ld\n", cf->content_length, cf->blksz, cf->segbc);
}
fwrite(&cf->time, sizeof(long), 1, fp);
fwrite(&cf->content_length, sizeof(off_t), 1, fp);
fwrite(&cf->blksz, sizeof(int), 1, fp);
fwrite(&cf->segbc, sizeof(long), 1, fp);
fwrite(cf->seg, sizeof(Seg), cf->segbc, fp);
/* Error checking for fwrite */
if (ferror(fp)) {
fprintf(stderr,
"Meta_write(): fwrite(): encountered error!\n");
return -1;
}
return 0;
}
/**
* \brief create a data file
* \details We use sparse creation here
* \return
* - 0 on successful creation of the data file, note that the result of
* the ftruncate() is ignored.
* - -1 on failure to create the data file.
*/
static int Data_create(Cache *cf)
{
int fd;
int mode;
mode = S_IRUSR | S_IWUSR | S_IRGRP | S_IROTH;
char *datafn = path_append(DATA_DIR, cf->path);
fd = open(datafn, O_WRONLY | O_CREAT, mode);
free(datafn);
if (fd == -1) {
fprintf(stderr, "Data_create(): open(): %s\n", strerror(errno));
return -1;
}
if (ftruncate(fd, cf->content_length)) {
fprintf(stderr, "Data_create(): ftruncate(): %s\n", strerror(errno));
}
if (close(fd)) {
fprintf(stderr, "Data_create(): close:(): %s\n", strerror(errno));
}
return 0;
}
/**
* \brief obtain the data file size
*/
static long Data_size(const char *fn)
{
char *datafn = path_append(DATA_DIR, fn);
struct stat st;
int s = stat(datafn, &st);
free(datafn);
if (!s) {
return st.st_size;
}
fprintf(stderr, "Data_size(): stat(): %s\n", strerror(errno));
return -1;
}
/**
* \brief read a data file
* \param[in] cf the pointer to the cache in-memory data structure
* \param[out] buf the output buffer
* \param[in] len the length of the segment
* \param[in] offset the offset of the segment
* \return
* - negative values on error,
* - otherwise, the number of bytes read.
*/
static long Data_read(Cache *cf, uint8_t *buf, off_t len, off_t offset)
{
if (len == 0) {
fprintf(stderr, "Data_read(): requested to read 0 byte!\n");
return -EINVAL;
}
if (fseeko(cf->dfp, offset, SEEK_SET)) {
/* fseeko failed */
fprintf(stderr, "Data_read(): fseeko(): %s\n", strerror(errno));
return -EIO;
}
long byte_read = fread(buf, sizeof(uint8_t), len, cf->dfp);
if (byte_read != len) {
fprintf(stderr,
"Data_read(): fread(): requested %ld, returned %ld!\n",
len, byte_read);
if (feof(cf->dfp)) {
/* reached EOF */
fprintf(stderr,
"Data_read(): fread(): reached the end of the file!\n");
}
if (ferror(cf->dfp)) {
/* filesystem error */
fprintf(stderr,
"Data_read(): fread(): encountered error!\n");
}
}
return byte_read;
}
/**
* \brief write to a data file
* \param[in] cf the pointer to the cache in-memory data structure
* \param[in] buf the input buffer
* \param[in] len the length of the segment
* \param[in] offset the offset of the segment
* \return
* - -1 when the data file does not exist
* - otherwise, the number of bytes written.
*/
static long Data_write(Cache *cf, const uint8_t *buf, off_t len,
off_t offset)
{
if (len == 0) {
fprintf(stderr, "Data_write(): requested to write 0 byte!\n");
return -EINVAL;
}
if (fseeko(cf->dfp, offset, SEEK_SET)) {
/* fseeko failed */
fprintf(stderr, "Data_write(): fseeko(): %s\n", strerror(errno));
return -EIO;
}
long byte_written = fwrite(buf, sizeof(uint8_t), len, cf->dfp);
if (byte_written != len) {
fprintf(stderr,
"Data_write(): fwrite(): requested %ld, returned %ld!\n",
len, byte_written);
if (ferror(cf->dfp)) {
/* filesystem error */
fprintf(stderr,
"Data_write(): fwrite(): encountered error!\n");
}
}
return byte_written;
}
int CacheDir_create(const char *dirn)
{
char *metadirn = path_append(META_DIR, dirn);
char *datadirn = path_append(DATA_DIR, dirn);
int i;
i = -mkdir(metadirn, S_IRWXU | S_IRWXG | S_IROTH | S_IXOTH);
if (i && (errno != EEXIST)) {
fprintf(stderr, "CacheDir_create(): mkdir(): %s\n", strerror(errno));
}
i |= -mkdir(datadirn, S_IRWXU | S_IRWXG | S_IROTH | S_IXOTH) << 1;
if (i && (errno != EEXIST)) {
fprintf(stderr, "CacheDir_create(): mkdir(): %s\n", strerror(errno));
}
return -i;
}
/**
* \brief Allocate a new cache data structure
*/
static Cache *Cache_alloc()
{
Cache *cf = calloc(1, sizeof(Cache));
if (!cf) {
fprintf(stderr, "Cache_new(): calloc failure!\n");
exit(EXIT_FAILURE);
}
if (pthread_mutexattr_init(&cf->rw_lock_attr)) {
fprintf(stderr,
"Cache_alloc(): rw_lock_attr initialisation failed!\n");
}
if (pthread_mutexattr_setpshared(&cf->rw_lock_attr,
PTHREAD_PROCESS_SHARED)) {
fprintf(stderr, "Cache_alloc(): could not set rw_lock_attr!\n");
}
if (pthread_mutex_init(&cf->rw_lock, &cf->rw_lock_attr)) {
fprintf(stderr, "Cache_alloc(): rw_lock initialisation failed!\n");
}
if (pthread_mutexattr_init(&cf->bgt_lock_attr)) {
fprintf(stderr,
"Cache_alloc(): bgt_lock_attr initialisation failed!\n");
}
if (pthread_mutexattr_setpshared(&cf->bgt_lock_attr,
PTHREAD_PROCESS_SHARED)) {
fprintf(stderr, "Cache_alloc(): could not set bgt_lock_attr!\n");
}
if (pthread_mutex_init(&cf->bgt_lock, &cf->bgt_lock_attr)) {
fprintf(stderr, "Cache_alloc(): bgt_lock initialisation failed!\n");
}
return cf;
}
/**
* \brief free a cache data structure
*/
static void Cache_free(Cache *cf)
{
if (pthread_mutex_destroy(&cf->rw_lock)) {
fprintf(stderr, "Cache_free(): could not destroy rw_lock!\n");
}
if (pthread_mutexattr_destroy(&cf->rw_lock_attr)) {
fprintf(stderr, "Cache_alloc(): could not destroy rw_lock_attr!\n");
}
if (pthread_mutex_destroy(&cf->bgt_lock)) {
fprintf(stderr, "Cache_free(): could not destroy bgt_lock!\n");
}
if (pthread_mutexattr_destroy(&cf->bgt_lock_attr)) {
fprintf(stderr, "Cache_alloc(): could not destroy bgt_lock_attr!\n");
}
if (cf->path) {
free(cf->path);
}
if (cf->seg) {
free(cf->seg);
}
free(cf);
}
/**
* \brief Check if both metadata and data file exist, otherwise perform cleanup.
* \details
* This function checks if both metadata file and the data file exist. If that
* is not the case, clean up is performed - the existing unpaired metadata file
* or data file is deleted.
* \return
* - 0, if both metadata and cache file exist
* - -1, otherwise
*/
static int Cache_exist(const char *fn)
{
int meta_exists = 1;
int data_exists = 1;
char *metafn = path_append(META_DIR, fn);
char *datafn = path_append(DATA_DIR, fn);
if (access(metafn, F_OK)) {
// fprintf(stderr, "Cache_exist(): access(): %s\n", strerror(errno));
meta_exists = 0;
}
if (access(datafn, F_OK)) {
// fprintf(stderr, "Cache_exist(): access(): %s\n", strerror(errno));
data_exists = 0;
}
if (meta_exists ^ data_exists) {
if (meta_exists) {
if(unlink(metafn)) {
fprintf(stderr, "Cache_exist(): unlink(): %s\n",
strerror(errno));
}
}
if (data_exists) {
if(unlink(datafn)) {
fprintf(stderr, "Cache_exist(): unlink(): %s\n",
strerror(errno));
}
}
}
free(metafn);
free(datafn);
return meta_exists & data_exists;
}
/**
* \brief delete a cache file set
*/
void Cache_delete(const char *fn)
{
char *metafn = path_append(META_DIR, fn);
char *datafn = path_append(DATA_DIR, fn);
if (!access(metafn, F_OK)) {
if(unlink(metafn)) {
fprintf(stderr, "Cache_delete(): unlink(): %s\n",
strerror(errno));
}
}
if (!access(datafn, F_OK)) {
if(unlink(datafn)) {
fprintf(stderr, "Cache_delete(): unlink(): %s\n",
strerror(errno));
}
}
free(metafn);
free(datafn);
}
/**
* \brief Open the data file of a cache data set
* \return
* - 0 on success
* - -1 on failure, with appropriate errno set.
*/
static int Data_open(Cache *cf)
{
char *datafn = path_append(DATA_DIR, cf->path);
cf->dfp = fopen(datafn, "r+");
free(datafn);
if (!cf->dfp) {
/* Failed to open the data file */
fprintf(stderr, "Data_open(): fopen(%s): %s\n", datafn,
strerror(errno));
return -1;
}
return 0;
}
/**
* \brief Open a metafile
* \return
* - 0 on success
* - -1 on failure, with appropriate errno set.
*/
static int Meta_open(Cache *cf)
{
char *metafn = path_append(META_DIR, cf->path);
cf->mfp = fopen(metafn, "r+");
if (!cf->mfp) {
/* Failed to open the data file */
fprintf(stderr, "Meta_open(): fopen(%s): %s\n", metafn,
strerror(errno));
free(metafn);
return -1;
}
free(metafn);
return 0;
}
/**
* \brief Create a metafile
* \return
* - 0 on success
* - -1 on failure, with appropriate errno set.
*/
static int Meta_create(Cache *cf)
{
char *metafn = path_append(META_DIR, cf->path);
cf->mfp = fopen(metafn, "w");
if (!cf->mfp) {
/* Failed to open the data file */
fprintf(stderr, "Meta_create(): fopen(%s): %s\n", metafn,
strerror(errno));
free(metafn);
return -1;
}
free(metafn);
return 0;
}
int Cache_create(Link *this_link)
{
char *fn;
fn = curl_easy_unescape(NULL, this_link->f_url + ROOT_LINK_OFFSET, 0, NULL);
fprintf(stderr, "Cache_create(): Creating cache files for %s.\n", fn);
Cache *cf = Cache_alloc();
cf->path = strndup(fn, MAX_PATH_LEN);
cf->time = this_link->time;
cf->content_length = this_link->content_length;
cf->blksz = DATA_BLK_SZ;
cf->segbc = (cf->content_length / cf->blksz) + 1;
cf->seg = calloc(cf->segbc, sizeof(Seg));
if (!cf->seg) {
fprintf(stderr, "Cache_create(): cf->seg calloc failure!\n");
exit(EXIT_FAILURE);
}
if (Meta_create(cf)) {
fprintf(stderr, "Cache_create(): cannot create metadata.\n");
}
if (fclose(cf->mfp)) {
fprintf(stderr,
"Cache_create(): cannot close metadata after creation: %s.\n",
strerror(errno));
}
if (Meta_open(cf)) {
Cache_free(cf);
fprintf(stderr, "Cache_create(): cannot open metadata file, %s.\n", fn);
}
if (Meta_write(cf)) {
fprintf(stderr, "Cache_create(): Meta_write() failed!\n");
}
if (fclose(cf->mfp)) {
fprintf(stderr,
"Cache_create(): cannot close metadata after write, %s.\n",
strerror(errno));
}
if (Data_create(cf)) {
fprintf(stderr, "Cache_create(): Data_create() failed!\n");
}
Cache_free(cf);
/*
* Cache_exist() returns 1, if cache files exist and valid. Whereas this
* function returns 0 on success.
*/
int res = -(!Cache_exist(fn));
curl_free(fn);
return res;
}
Cache *Cache_open(const char *fn)
{
/* Check if both metadata and data file exist */
if (!Cache_exist(fn)) {
return NULL;
}
/* Obtain the link structure memory pointer */
Link *link = path_to_Link(fn);
if (!link) {
return NULL;
}
/*---------------- Cache_open() critical section -----------------*/
#ifdef CACHE_LOCK_DEBUG
fprintf(stderr, "Cache_open(): thread %lu: locking cf_lock;\n",
pthread_self());
#endif
PTHREAD_MUTEX_LOCK(&cf_lock);
if (link->cache_opened) {
link->cache_opened++;
#ifdef CACHE_LOCK_DEBUG
fprintf(stderr, "Cache_open(): thread %lu: unlocking cf_lock;\n",
pthread_self());
#endif
PTHREAD_MUTEX_UNLOCK(&cf_lock);
return link->cache_ptr;
}
#ifdef CACHE_LOCK_DEBUG
fprintf(stderr, "Cache_open(): thread %lu: unlocking cf_lock;\n",
pthread_self());
#endif
PTHREAD_MUTEX_UNLOCK(&cf_lock);
/*----------------------------------------------------------------*/
/* Create the cache in-memory data structure */
Cache *cf = Cache_alloc();
cf->path = strndup(fn, MAX_PATH_LEN);
/* Associate the cache structure with a link */
cf->link = link;
if (Meta_open(cf)) {
Cache_free(cf);
fprintf(stderr, "Cache_open(): cannot open metadata file %s.\n", fn);
return NULL;
}
int rtn = Meta_read(cf);
/*
* Internally inconsistent or corrupt metadata
*/
if ((rtn == EINCONSIST) || (rtn == EZERO) || (rtn == EMEM)) {
Cache_free(cf);
fprintf(stderr, "Cache_open(): metadata error: %s, %d.\n", fn, rtn);
return NULL;
}
/*
* Inconsistency between metadata and data file, note that on disk file
* size might be bigger than content_length, due to on-disk filesystem
* allocation policy.
*/
if (cf->content_length > Data_size(fn)) {
fprintf(stderr, "Cache_open(): metadata inconsistency %s, \
cf->content_length: %ld, Data_size(fn): %ld.\n", fn, cf->content_length,
Data_size(fn));
Cache_free(cf);
return NULL;
}
/* Check if the cache files are not outdated */
if (cf->time != cf->link->time) {
fprintf(stderr, "Cache_open(): outdated cache file: %s.\n", fn);
Cache_free(cf);
return NULL;
}
if (Data_open(cf)) {
Cache_free(cf);
fprintf(stderr, "Cache_open(): cannot open data file %s.\n", fn);
return NULL;
}
cf->link->cache_opened = 1;
/* Yup, we just created a circular loop. ;) */
cf->link->cache_ptr = cf;
return cf;
}
void Cache_close(Cache *cf)
{
/*--------------- Cache_close() critical section -----------------*/
#ifdef CACHE_LOCK_DEBUG
fprintf(stderr, "Cache_close(): thread %lu: locking cf_lock;\n",
pthread_self());
#endif
PTHREAD_MUTEX_LOCK(&cf_lock);
cf->link->cache_opened--;
if (cf->link->cache_opened > 0) {
#ifdef CACHE_LOCK_DEBUG
fprintf(stderr, "Cache_close(): thread %lu: unlocking cf_lock;\n",
pthread_self());
#endif
PTHREAD_MUTEX_UNLOCK(&cf_lock);
return;
}
#ifdef CACHE_LOCK_DEBUG
fprintf(stderr, "Cache_close(): thread %lu: unlocking cf_lock;\n",
pthread_self());
#endif
PTHREAD_MUTEX_UNLOCK(&cf_lock);
/*----------------------------------------------------------------*/
if (Meta_write(cf)) {
fprintf(stderr, "Cache_close(): Meta_write() error.");
}
if (fclose(cf->mfp)) {
fprintf(stderr, "Cache_close(): cannot close metadata: %s.\n",
strerror(errno));
}
if (fclose(cf->dfp)) {
fprintf(stderr, "Cache_close(): cannot close data file %s.\n",
strerror(errno));
}
return Cache_free(cf);
}
/**
* \brief Check if a segment exists.
* \return 1 if the segment exists
*/
static int Seg_exist(Cache *cf, off_t offset)
{
off_t byte = offset / cf->blksz;
return cf->seg[byte];
}
/**
* \brief Set the existence of a segment
* \param[in] cf the cache in-memory data structure
* \param[in] offset the starting position of the segment.
* \param[in] i 1 for exist, 0 for doesn't exist
* \note Call this after downloading a segment.
*/
static void Seg_set(Cache *cf, off_t offset, int i)
{
off_t byte = offset / cf->blksz;
cf->seg[byte] = i;
}
/**
* \brief Background download function
* \details If we are requesting the data from the second half of the current
* segment, we can spawn a pthread using this function to download the next
* segment.
*/
static void *Cache_bgdl(void *arg)
{
Cache *cf = (Cache *) arg;
#ifdef CACHE_LOCK_DEBUG
fprintf(stderr, "Cache_bgdl(): thread %lu: locking rw_lock;\n",
pthread_self());
#endif
PTHREAD_MUTEX_LOCK(&cf->rw_lock);
uint8_t *recv_buf = calloc(cf->blksz, sizeof(uint8_t));
fprintf(stderr, "Cache_bgdl(): thread %lu:", pthread_self());
long recv = path_download(cf->path, (char *) recv_buf, cf->blksz,
cf->next_offset);
if ( (recv == cf->blksz) ||
(cf->next_offset == (cf->content_length / cf->blksz * cf->blksz)) )
{
Data_write(cf, recv_buf, cf->blksz, cf->next_offset);
Seg_set(cf, cf->next_offset, 1);
} else {
fprintf(stderr,
"Cache_bgdl(): received %ld, possible network error.\n", recv);
}
free(recv_buf);
#ifdef CACHE_LOCK_DEBUG
fprintf(stderr, "Cache_bgdl(): thread %lu: unlocking bgt_lock;\n",
pthread_self());
#endif
PTHREAD_MUTEX_UNLOCK(&cf->bgt_lock);
#ifdef CACHE_LOCK_DEBUG
fprintf(stderr, "Cache_bgdl(): thread %lu: unlocking rw_lock;\n",
pthread_self());
#endif
PTHREAD_MUTEX_UNLOCK(&cf->rw_lock);
pthread_detach(pthread_self());
pthread_exit(NULL);
}
long Cache_read(Cache *cf, char *output_buf, off_t len, off_t offset)
{
size_t start = offset;
size_t end = start + len;
char range_str[64];
snprintf(range_str, sizeof(range_str), "%lu-%lu", start, end);
fprintf(stderr, "Cache_read(): thread %lu: %s, %s;\n", pthread_self(),
cf->path, range_str);
/* SIGFPE prevention, although this shouldn't happen in the first place! */
if (!cf->blksz) {
fprintf(stderr,
"Cache_read(): Warning: cf->blksz: %d, directly downloading",
cf->blksz);
return path_download(cf->path, output_buf, len, offset);
}
long send;
off_t dl_offset = offset / cf->blksz * cf->blksz;
/* ------------------ Check if the segment already exists ---------------*/
if (Seg_exist(cf, offset)) {
send = Data_read(cf, (uint8_t *) output_buf, len, offset);
goto bgdl;
} else {
#ifdef CACHE_LOCK_DEBUG
fprintf(stderr,
"Cache_read(): thread %lu: locking and unlocking bgt_lock;\n",
pthread_self());
#endif
/* Wait for the background download thread to finish */
PTHREAD_MUTEX_LOCK(&cf->bgt_lock);
PTHREAD_MUTEX_UNLOCK(&cf->bgt_lock);
#ifdef CACHE_LOCK_DEBUG
fprintf(stderr, "Cache_read(): thread %lu: locking rw_lock;\n",
pthread_self());
#endif
/* Wait for any other download thread to finish*/
PTHREAD_MUTEX_LOCK(&cf->rw_lock);
if (Seg_exist(cf, offset)) {
/* The segment now exists - it was downloaded by another
* download thread. Send it off and unlock the I/O */
send = Data_read(cf, (uint8_t *) output_buf, len, offset);
#ifdef CACHE_LOCK_DEBUG
fprintf(stderr, "Cache_read(): thread %lu: unlocking rw_lock;\n",
pthread_self());
#endif
PTHREAD_MUTEX_UNLOCK(&cf->rw_lock);
goto bgdl;
}
}
/* ------------------------Download the segment -------------------------*/
uint8_t *recv_buf = calloc(cf->blksz, sizeof(uint8_t));
fprintf(stderr, "Cache_read(): ");
long recv = path_download(cf->path, (char *) recv_buf, cf->blksz,
dl_offset);
/*
* check if we have received enough data
* send it off, then write it to the disk
*
* Condition 1: received the exact amount as the segment size.
* Condition 2: offset is the last segment
*/
if ( (recv == cf->blksz) ||
(dl_offset == (cf->content_length / cf->blksz * cf->blksz)) )
{
memmove(output_buf, recv_buf + (offset - dl_offset), len);
send = len;
Data_write(cf, recv_buf, cf->blksz, dl_offset);
Seg_set(cf, dl_offset, 1);
} else {
memmove(output_buf, recv_buf + (offset - dl_offset), recv);
send = recv;
fprintf(stderr,
"Cache_read(): received %ld, possible network error.\n", recv);
}
free(recv_buf);
#ifdef CACHE_LOCK_DEBUG
fprintf(stderr, "Cache_read(): thread %lu: unlocking rw_lock;\n",
pthread_self());
#endif
PTHREAD_MUTEX_UNLOCK(&cf->rw_lock);
/* -----------Download the next segment in background -------------------*/
bgdl:
cf->next_offset = round_div(offset, cf->blksz) * cf->blksz;
if ( (cf->next_offset > dl_offset) &&
!Seg_exist(cf, cf->next_offset) &&
cf->next_offset < cf->content_length ){
/* Stop the spawning of multiple background pthreads */
if(!pthread_mutex_trylock(&cf->bgt_lock)) {
#ifdef CACHE_LOCK_DEBUG
fprintf(stderr, "Cache_read(): thread %lu: trylocked bgt_lock;\n",
pthread_self());
#endif
if (pthread_create(&cf->bgt, NULL, Cache_bgdl, cf)) {
fprintf(stderr,
"Cache_read(): Error creating background download thread\n"
);
}
}
}
return send;
}
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