KDECore
#include <kshareddatacache.h>
Public Types | |
enum | EvictionPolicy { NoEvictionPreference = 0, EvictLeastRecentlyUsed, EvictLeastOftenUsed, EvictOldest } |
Public Member Functions | |
KSharedDataCache (const QString &cacheName, unsigned defaultCacheSize, unsigned expectedItemSize=0) | |
~KSharedDataCache () | |
void | clear () |
bool | contains (const QString &key) const |
EvictionPolicy | evictionPolicy () const |
bool | find (const QString &key, QByteArray *destination) const |
unsigned | freeSize () const |
bool | insert (const QString &key, const QByteArray &data) |
void | setEvictionPolicy (EvictionPolicy newPolicy) |
void | setTimestamp (unsigned newTimestamp) |
unsigned | timestamp () const |
unsigned | totalSize () const |
Static Public Member Functions | |
static void | deleteCache (const QString &cacheName) |
Detailed Description
A simple data cache which uses shared memory to quickly access data stored on disk.
This class is meant to be used with KImageCache and similar classes but can be used directly if used with care.
Example usage:
- See also
- KImageCache
- Since
- 4.5
Definition at line 58 of file kshareddatacache.h.
Member Enumeration Documentation
Enumerator | |
---|---|
NoEvictionPreference | |
EvictLeastRecentlyUsed | |
EvictLeastOftenUsed | |
EvictOldest |
Definition at line 83 of file kshareddatacache.h.
Constructor & Destructor Documentation
KSharedDataCache::KSharedDataCache | ( | const QString & | cacheName, |
unsigned | defaultCacheSize, | ||
unsigned | expectedItemSize = 0 |
||
) |
Attaches to a shared cache, creating it if necessary.
If supported, this data cache will be shared across all processes using this cache (with subsequent memory savings). If shared memory is unsupported or a failure occurs, caching will still be supported, but only in the same process, and only using the same KSharedDataCache object.
- Parameters
-
cacheName Name of the cache to use/share. defaultCacheSize Amount of data to be able to store, in bytes. The actual size will be slightly larger on disk due to accounting overhead. If the cache already existed then it will not be resized. For this reason you should specify some reasonable size. expectedItemSize The average size of an item that would be stored in the cache, in bytes. Choosing an average size of zero bytes causes KSharedDataCache to use whatever it feels is the best default for the system.
Definition at line 1398 of file kshareddatacache.cpp.
KSharedDataCache::~KSharedDataCache | ( | ) |
Definition at line 1422 of file kshareddatacache.cpp.
Member Function Documentation
void KSharedDataCache::clear | ( | ) |
Removes all entries from the cache.
Definition at line 1647 of file kshareddatacache.cpp.
Returns true if the cache currently contains the image for the given filename.
NOTE: Calling this function is threadsafe, but it is in general not possible to guarantee the image stays cached immediately afterwards, so if you need the result use find().
Definition at line 1661 of file kshareddatacache.cpp.
|
static |
Removes the underlying file from the cache.
Note that this is all that this function does. The shared memory segment is still attached and will still contain all the data until all processes currently attached remove the mapping.
In order to remove the data see clear().
Definition at line 1677 of file kshareddatacache.cpp.
KSharedDataCache::EvictionPolicy KSharedDataCache::evictionPolicy | ( | ) | const |
- Returns
- The removal policy in use by the shared cache.
- See also
- EvictionPolicy
Definition at line 1720 of file kshareddatacache.cpp.
bool KSharedDataCache::find | ( | const QString & | key, |
QByteArray * | destination | ||
) | const |
Returns the data in the cache named by key
(even if it's some other process's data named with the same key!), stored in destination
.
If there is no entry named by key
then destination
is left unchanged. The return value is used to tell what happened.
If you simply want to verify whether an entry is present in the cache then see contains().
- Parameters
-
key The key to find in the cache. destination Is set to the value of key
in the cache ifkey
is present, left unchanged otherwise.
- Returns
- true if
key
was present in the cache (destination
will also be updated), false ifkey
was not present (destination
will be unchanged).
Definition at line 1603 of file kshareddatacache.cpp.
unsigned KSharedDataCache::freeSize | ( | ) | const |
Returns the amount of free space in the cache, in bytes.
Due to implementation details it is possible to still not be able to fit an entry in the cache at any given time even if it is smaller than the amount of space remaining.
Definition at line 1704 of file kshareddatacache.cpp.
bool KSharedDataCache::insert | ( | const QString & | key, |
const QByteArray & | data | ||
) |
Attempts to insert the entry data
into the shared cache, named by key
, and returns true only if successful.
Note that even if the insert was successful, that the newly added entry may be evicted by other processes contending for the cache.
Definition at line 1444 of file kshareddatacache.cpp.
void KSharedDataCache::setEvictionPolicy | ( | KSharedDataCache::EvictionPolicy | newPolicy | ) |
Sets the entry removal policy for the shared cache to newPolicy
.
The default is EvictionPolicy::NoEvictionPreference.
- See also
- EvictionPolicy
Definition at line 1729 of file kshareddatacache.cpp.
void KSharedDataCache::setTimestamp | ( | unsigned | newTimestamp | ) |
Sets the shared timestamp of the cache.
Timestamping is supported to allow applications to more effectively "version" the data stored in the cache. However, the timestamp is shared with all applications using the cache so you should always be prepared for invalid timestamps.
When the cache is first created (note that this is different from attaching to an existing shared cache on disk), the cache timestamp is initialized to the time returned by time(2)
. KSharedDataCache will not update the timestamp again, it is only updated through this method.
Example:
- Parameters
-
newTimestamp The new timestamp to mark the shared cache with.
- See also
- timestamp()
- Since
- 4.6
Definition at line 1745 of file kshareddatacache.cpp.
unsigned KSharedDataCache::timestamp | ( | ) | const |
- Returns
- The shared timestamp of the cache. The interpretation of the timestamp returned is up to the application. KSharedDataCache will initialize the timestamp to the time returned by
time(2)
on cache creation, but KSharedDataCache will not touch the timestamp again.
- See also
- setTimestamp()
- Since
- 4.6
Definition at line 1736 of file kshareddatacache.cpp.
unsigned KSharedDataCache::totalSize | ( | ) | const |
Returns the usable cache size in bytes.
The actual amount of memory used will be slightly larger than this to account for required accounting overhead.
Definition at line 1688 of file kshareddatacache.cpp.
The documentation for this class was generated from the following files:
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