libdap Updated for version 3.20.10
libdap4 is an implementation of OPeNDAP's DAP protocol.
libdap::HTTPCacheTable Class Reference

#include <HTTPCacheTable.h>

Classes

struct  CacheEntry
 

Public Types

typedef vector< CacheEntry * > CacheEntries
 
typedef CacheEntries::iterator CacheEntriesIter
 
typedef CacheEntries ** CacheTable
 

Public Member Functions

void delete_by_hits (int hits)
 
void delete_by_size (unsigned int size)
 
void delete_expired_entries (time_t time=0)
 
unsigned int get_block_size () const
 
string get_cache_root ()
 
unsigned long get_current_size () const
 
int get_new_entries () const
 
 HTTPCacheTable (const string &cache_root, int block_size)
 
void increment_new_entries ()
 
void set_block_size (unsigned int sz)
 
void set_cache_root (const string &cr)
 
void set_current_size (unsigned long sz)
 
Cache Index

These methods manage the cache's index file. Each cache holds an index file named .index which stores the cache's state information.

bool cache_index_delete ()
 
bool cache_index_read ()
 
CacheEntrycache_index_parse_line (const char *line)
 
void cache_index_write ()
 
string create_hash_directory (int hash)
 
void create_location (CacheEntry *entry)
 

Friends

class HTTPCacheTest
 

Methods to manipulate instances of CacheEntry.

void delete_all_entries ()
 
void add_entry_to_cache_table (CacheEntry *entry)
 
void remove_cache_entry (HTTPCacheTable::CacheEntry *entry)
 
void remove_entry_from_cache_table (const string &url)
 
CacheEntryget_locked_entry_from_cache_table (const string &url)
 
CacheEntryget_write_locked_entry_from_cache_table (const string &url)
 
void calculate_time (HTTPCacheTable::CacheEntry *entry, int default_expiration, time_t request_time)
 
void parse_headers (HTTPCacheTable::CacheEntry *entry, unsigned long max_entry_size, const vector< string > &headers)
 
void bind_entry_to_data (CacheEntry *entry, FILE *body)
 
void uncouple_entry_from_data (FILE *body)
 
bool is_locked_read_responses ()
 

Detailed Description

The table of entries in the client-side cache. This class maintains a table of CacheEntries, where one instance of CacheEntry is made for each item in the cache. When an item is accessed it is either locked for reading or writing. When locked for reading the entry is recorded on a list of read-locked entries. The caller must explicitly free the entry for it to be removed from this list (which is the only way it can be opened for writing). An entry can be accessed by multiple readers but only one writer.

Note
The CacheEntry class used to contain a lock that was used to ensure that the entry was locked during any changes to any of its fields. That has been removed - its now the responsibility of the caller. This change was made because it's likely the caller will need to lock all of the methods that operate on a CacheEntry anyway, so the CacheEntry-specific lock was redundant.

Definition at line 101 of file HTTPCacheTable.h.

Member Typedef Documentation

◆ CacheEntries

typedef vector<CacheEntry *> libdap::HTTPCacheTable::CacheEntries

Definition at line 266 of file HTTPCacheTable.h.

◆ CacheEntriesIter

typedef CacheEntries::iterator libdap::HTTPCacheTable::CacheEntriesIter

Definition at line 267 of file HTTPCacheTable.h.

◆ CacheTable

typedef CacheEntries** libdap::HTTPCacheTable::CacheTable

Definition at line 269 of file HTTPCacheTable.h.

Constructor & Destructor Documentation

◆ HTTPCacheTable()

libdap::HTTPCacheTable::HTTPCacheTable ( const string & cache_root,
int block_size )

Definition at line 113 of file HTTPCacheTable.cc.

◆ ~HTTPCacheTable()

libdap::HTTPCacheTable::~HTTPCacheTable ( )

Definition at line 137 of file HTTPCacheTable.cc.

Member Function Documentation

◆ add_entry_to_cache_table()

void libdap::HTTPCacheTable::add_entry_to_cache_table ( CacheEntry * entry)

Add a CacheEntry to the cache table. As each entry is read, load it into the in-memory cache table and update the HTTPCache's current_size. The later is used by the garbage collection method.

Parameters
entryThe CacheEntry instance to add.

Definition at line 562 of file HTTPCacheTable.cc.

◆ bind_entry_to_data()

void libdap::HTTPCacheTable::bind_entry_to_data ( HTTPCacheTable::CacheEntry * entry,
FILE * body )

Definition at line 865 of file HTTPCacheTable.cc.

◆ cache_index_delete()

bool libdap::HTTPCacheTable::cache_index_delete ( )

Remove the cache index file.

A private method.

Returns
True if the file was deleted, otherwise false.

Definition at line 282 of file HTTPCacheTable.cc.

◆ cache_index_parse_line()

HTTPCacheTable::CacheEntry * libdap::HTTPCacheTable::cache_index_parse_line ( const char * line)

Parse one line of the index file.

A private method.

Parameters
lineA single line from the .index file.
Returns
A CacheEntry initialized with the information from line.

Definition at line 331 of file HTTPCacheTable.cc.

◆ cache_index_read()

bool libdap::HTTPCacheTable::cache_index_read ( )

Read the saved set of cached entries from disk. Consistency between the in-memory cache and the index is maintained by only reading the index file when the HTTPCache object is created!

A private method.

Returns
True when a cache index was found and read, false otherwise.

Definition at line 298 of file HTTPCacheTable.cc.

◆ cache_index_write()

void libdap::HTTPCacheTable::cache_index_write ( )

Walk through the list of cached objects and write the cache index file to disk. If the file does not exist, it is created. If the file does exist, it is overwritten. As a side effect, zero the new_entries counter.

A private method.

Exceptions
ErrorThrown if the index file cannot be opened for writing.
Note
The HTTPCache destructor calls this method and silently ignores this exception.

Definition at line 402 of file HTTPCacheTable.cc.

◆ calculate_time()

void libdap::HTTPCacheTable::calculate_time ( HTTPCacheTable::CacheEntry * entry,
int default_expiration,
time_t request_time )

Calculate the corrected_initial_age of the object. We use the time when this function is called as the response_time as this is when we have received the complete response. This may cause a delay if the response header is very big but should not cause any incorrect behavior.

A private method.

Parameters
entryThe CacheEntry object.
default_expirationThe default value of the cached object's expiration time.
request_timeWhen was the request made? I think this value must be passed into the method that calls this method...

Definition at line 761 of file HTTPCacheTable.cc.

◆ create_hash_directory()

string libdap::HTTPCacheTable::create_hash_directory ( int hash)

Create the directory path for cache file. The cache uses a set of directories within d_cache_root to store individual responses. The name of the directory that holds a given response is the value returned by the get_hash() function (i.e., it's a number). If the directory exists, this method does nothing.

A private method.

Parameters
hashThe hash value (i.e., directory name). An integer between 0 and CACHE_TABLE_SIZE (See HTTPCache.h).
Returns
The pathname to the directory (even if it already existed).
Exceptions
ErrorThrown if the directory cannot be created.

Definition at line 447 of file HTTPCacheTable.cc.

◆ create_location()

void libdap::HTTPCacheTable::create_location ( HTTPCacheTable::CacheEntry * entry)

Create the directory for this url (using the hash value from get_hash()) and a file within that directory to hold the response's information. The cache name and cache_body_fd fields of entry are updated.

mkstemp opens the file it creates, which is a good thing but it makes tracking resources hard for the HTTPCache object (because an exception might cause a file descriptor resource leak). So I close that file descriptor here.

A private method.

Parameters
entryThe cache entry object to operate on.
Exceptions
ErrorIf the file for the response's body cannot be created.

Definition at line 505 of file HTTPCacheTable.cc.

◆ delete_all_entries()

void libdap::HTTPCacheTable::delete_all_entries ( )

Definition at line 732 of file HTTPCacheTable.cc.

◆ delete_by_hits()

void libdap::HTTPCacheTable::delete_by_hits ( int hits)

Definition at line 220 of file HTTPCacheTable.cc.

◆ delete_by_size()

void libdap::HTTPCacheTable::delete_by_size ( unsigned int size)

Definition at line 255 of file HTTPCacheTable.cc.

◆ delete_expired_entries()

void libdap::HTTPCacheTable::delete_expired_entries ( time_t time = 0)

Definition at line 183 of file HTTPCacheTable.cc.

◆ get_block_size()

unsigned int libdap::HTTPCacheTable::get_block_size ( ) const
inline

Definition at line 311 of file HTTPCacheTable.h.

◆ get_cache_root()

string libdap::HTTPCacheTable::get_cache_root ( )
inline

Definition at line 329 of file HTTPCacheTable.h.

◆ get_current_size()

unsigned long libdap::HTTPCacheTable::get_current_size ( ) const
inline

Definition at line 302 of file HTTPCacheTable.h.

◆ get_locked_entry_from_cache_table()

HTTPCacheTable::CacheEntry * libdap::HTTPCacheTable::get_locked_entry_from_cache_table ( const string & url)

Get a pointer to a CacheEntry from the cache table.

Parameters
urlLook for this URL.

Definition at line 588 of file HTTPCacheTable.cc.

◆ get_new_entries()

int libdap::HTTPCacheTable::get_new_entries ( ) const
inline

Definition at line 320 of file HTTPCacheTable.h.

◆ get_write_locked_entry_from_cache_table()

HTTPCacheTable::CacheEntry * libdap::HTTPCacheTable::get_write_locked_entry_from_cache_table ( const string & url)

Get a pointer to a CacheEntry from the cache table. Providing a way to pass the hash code into this method makes it easier to test for correct behavior when two entries collide. 10/07/02 jhrg

Parameters
urlLook for this URL.
Returns
The matching CacheEntry instance or NULL if none was found.

Definition at line 627 of file HTTPCacheTable.cc.

◆ increment_new_entries()

void libdap::HTTPCacheTable::increment_new_entries ( )
inline

Definition at line 324 of file HTTPCacheTable.h.

◆ is_locked_read_responses()

bool libdap::HTTPCacheTable::is_locked_read_responses ( )

Definition at line 883 of file HTTPCacheTable.cc.

◆ parse_headers()

void libdap::HTTPCacheTable::parse_headers ( HTTPCacheTable::CacheEntry * entry,
unsigned long max_entry_size,
const vector< string > & headers )

Parse various headers from the vector (which can be retrieved from libcurl once a response is received) and load the CacheEntry object with values. This method should only be called with headers from a response (it should not be used to parse request headers).

A private method.

Parameters
entryStore values from the headers here.
max_entry_sizeDO not cache entries larger than this.
headersA vector of header lines.

Definition at line 804 of file HTTPCacheTable.cc.

◆ remove_cache_entry()

void libdap::HTTPCacheTable::remove_cache_entry ( HTTPCacheTable::CacheEntry * entry)

Remove a CacheEntry. This means delete the entry's files on disk and free the CacheEntry object. The caller should null the entry's pointer in the cache_table. The total size of the cache is decremented once the entry is deleted.

Parameters
entryThe CacheEntry to delete.
Exceptions
InternalErrThrown if entry is in use.

Definition at line 653 of file HTTPCacheTable.cc.

◆ remove_entry_from_cache_table()

void libdap::HTTPCacheTable::remove_entry_from_cache_table ( const string & url)

Find the CacheEntry for the given url and remove both its information in the persistent store and the entry in d_cache_table. If url is not in the cache, this method does nothing.

Parameters
urlRemove this URL's entry.
Exceptions
InternalErrThrown if the CacheEntry for url is locked.

Definition at line 701 of file HTTPCacheTable.cc.

◆ set_block_size()

void libdap::HTTPCacheTable::set_block_size ( unsigned int sz)
inline

Definition at line 315 of file HTTPCacheTable.h.

◆ set_cache_root()

void libdap::HTTPCacheTable::set_cache_root ( const string & cr)
inline

Definition at line 333 of file HTTPCacheTable.h.

◆ set_current_size()

void libdap::HTTPCacheTable::set_current_size ( unsigned long sz)
inline

Definition at line 306 of file HTTPCacheTable.h.

◆ uncouple_entry_from_data()

void libdap::HTTPCacheTable::uncouple_entry_from_data ( FILE * body)

Definition at line 870 of file HTTPCacheTable.cc.

Friends And Related Symbol Documentation

◆ HTTPCacheTest

friend class HTTPCacheTest
friend

Definition at line 271 of file HTTPCacheTable.h.


The documentation for this class was generated from the following files: