Abstract interface for a cache. More...

#include "shared_mem_cache.h"

Inheritance diagram for net_instaweb::SharedMemCache< kBlockSize >:

Public Member Functions
	SharedMemCache (AbstractSharedMem shm_runtime, const GoogleString &filename, Timer timer, const Hasher hasher, int sectors, int entries_per_sector, int blocks_per_sector, MessageHandler handler)
	code of ExtractPosition as well. More...

bool	Initialize ()

bool	Attach ()

size_t	MaxValueSize () const
	Returns the largest size of an object this cache can store.

GoogleString	DumpStats ()

bool	AddSectorToSnapshot (int sector_num, int64 last_checkpoint_ms, SharedMemCacheDump *dest)

void	RestoreSnapshot (const SharedMemCacheDump &dump)

virtual void	Get (const GoogleString &key, Callback *callback)

virtual void	Put (const GoogleString &key, const SharedString &value)

virtual void	Delete (const GoogleString &key)

virtual GoogleString	Name () const

virtual bool	IsBlocking () const

virtual bool	IsHealthy () const

virtual void	ShutDown ()

void	SanityCheck ()
	Sanity check the cache data structures.

void	RegisterSnapshotFileCache (FileCache *potential_file_cache, int checkpoint_interval_sec)

StringPiece	snapshot_path () const

FileCache *	file_cache () const

int64	GetLastWriteMsForTesting (int sector_num)

void	SetLastWriteMsForTesting (int sector_num, int64 last_checkpoint_ms)

void	WriteOutSnapshotForTesting (int sector_num, int64 last_checkpoint_ms)

Public Member Functions inherited from net_instaweb::CacheInterface
virtual void	MultiGet (MultiGetRequest *request)

void	PutSwappingString (const GoogleString &key, GoogleString *value)

virtual CacheInterface *	Backend ()

virtual bool	MustEncodeKeyInValueOnPut () const

virtual void	PutWithKeyInValue (const GoogleString &key, const SharedString &key_and_value)

Static Public Member Functions
static void	GlobalCleanup (AbstractSharedMem shm_runtime, const GoogleString &filename, MessageHandler message_handler)

static void	ComputeDimensions (int64 size_kb, int block_entry_ratio, int sectors, int entries_per_sector_out, int blocks_per_sector_out, int64 *size_cap_out)

static void	MarshalSnapshot (const SharedMemCacheDump &dump, GoogleString *out)
	Encode/Decode SharedMemCacheDump objects.

static void	DemarshalSnapshot (const StringPiece &marshaled, SharedMemCacheDump *out)

static GoogleString	FormatName ()

Static Public Member Functions inherited from net_instaweb::CacheInterface
static const char *	KeyStateName (KeyState state)

Static Public Attributes
static const int	kAssociativity = 4

Additional Inherited Members
Public Types inherited from net_instaweb::CacheInterface
enum	KeyState { kAvailable = 0, kNotFound = 1, kOverload = 2, kNetworkError = 3, kTimeout = 4 }

typedef std::vector< KeyCallback >	MultiGetRequest

Protected Member Functions inherited from net_instaweb::CacheInterface
void	ValidateAndReportResult (const GoogleString &key, KeyState state, Callback *callback)
	Invokes callback->ValidateCandidate() and callback->Done() as appropriate.

void	ReportMultiGetNotFound (MultiGetRequest *request)

Detailed Description

template<size_t kBlockSize>
class net_instaweb::SharedMemCache< kBlockSize >

Abstract interface for a cache.

Constructor & Destructor Documentation

template<size_t kBlockSize>

net_instaweb::SharedMemCache< kBlockSize >::SharedMemCache	(	AbstractSharedMem *	shm_runtime,
		const GoogleString &	filename,
		Timer *	timer,
		const Hasher *	hasher,
		int	sectors,
		int	entries_per_sector,
		int	blocks_per_sector,
		MessageHandler *	handler
	)

code of ExtractPosition as well.

Initializes the cache's settings, but does not actually touch the shared memory — you must call Initialize or Attach (and handle them potentially returning false) to do so. The filename parameter will be used to identify the shared memory segment, so distinct caches should use distinct values.

Callers who want checkpointing need to call RegisterSnapshotFileCache().

Precondition: hasher's raw mode must produce 13 bytes or more.

Member Function Documentation

template<size_t kBlockSize>

bool net_instaweb::SharedMemCache< kBlockSize >::AddSectorToSnapshot	(	int	sector_num,
		int64	last_checkpoint_ms,
		SharedMemCacheDump *	dest
	)

Tries to dump the contents the specified sector to *dest, aborts early if a different thread is already working on it, and returns whether it was successful. To make sure only one thread ends up dumping the sector it compares the last_checkpoint_ms provided to the one in the sector, and only continues with the dump if they match. After a successful dump, it updates the last_checkpoint_ms in the sector to the current time.

Note: other accesses to the sector will be locked out for the duration.

template<size_t kBlockSize>

bool net_instaweb::SharedMemCache< kBlockSize >::Attach ( )

Connects to already initialized state from a child process. It must be called once for every cache in every child process (that is, post-fork). Returns whether successful.

template<size_t kBlockSize>

static void net_instaweb::SharedMemCache< kBlockSize >::ComputeDimensions	(	int64	size_kb,
		int	block_entry_ratio,
		int	sectors,
		int *	entries_per_sector_out,
		int *	blocks_per_sector_out,
		int64 *	size_cap_out
	)

static

Computes how many entries and blocks per sector a cache with total size 'size_kb' and 'sectors' should have if there are about 'block_entry_ratio' worth of blocks of data per every entry. You probably want to underestimate this ratio somewhat, since having extra entries can reduce conflicts. Also outputs size_cap, which is the limit on object size for the resulting cache.

template<size_t kBlockSize>

GoogleString net_instaweb::SharedMemCache< kBlockSize >::DumpStats ( )

Returns some statistics as plaintext.

Todo:: TODO(morlovich): Potentially periodically push these to the main Statistics system (or pull to it from these).

template<size_t kBlockSize>

virtual void net_instaweb::SharedMemCache< kBlockSize >::Get	(	const GoogleString &	key,
		Callback *	callback
	)

virtual

Initiates a cache fetch, calling callback->ValidateCandidate() and then callback->Done(state) when done.

Note: implementations should normally invoke the callback via ValidateAndReportResult, which will combine ValidateCandidate() and Done() together properly.

Implements net_instaweb::CacheInterface.

template<size_t kBlockSize>

static void net_instaweb::SharedMemCache< kBlockSize >::GlobalCleanup	(	AbstractSharedMem *	shm_runtime,
		const GoogleString &	filename,
		MessageHandler *	message_handler
	)

static

This should be called from the root process as it is about to exit, when no further children are expected to start.

template<size_t kBlockSize>

bool net_instaweb::SharedMemCache< kBlockSize >::Initialize ( )

Sets up our shared state for use of all child processes/threads. Returns whether successful. This should be called exactly once for every cache in the root process, before forking.

If a file cache was set this restores any snapshotted sectors to shared memory.

template<size_t kBlockSize>

virtual bool net_instaweb::SharedMemCache< kBlockSize >::IsBlocking ( ) const

inlinevirtual

Returns true if this cache is guaranteed to call its callbacks before returning from Get and MultiGet.

Implements net_instaweb::CacheInterface.

template<size_t kBlockSize>

virtual bool net_instaweb::SharedMemCache< kBlockSize >::IsHealthy ( ) const

inlinevirtual

IsHealthy() is a rough estimation of whether cache is available for any operations. If it's false, caller may reasonably expect that making calls right now is useless as they will fail or have high latency. If it's true, operations should succeed, but some still may fail occasionally. The primary goal is to avoid sending commands to 'unhealthy' caches, e.g. if cache is under heavy load, we do not want to send even more requests.

Memory and file-based caches can simply return 'true'. It should be safe to call this frequently – the implementation shouldn't do much more that check a bool flag under mutex.

Implements net_instaweb::CacheInterface.

template<size_t kBlockSize>

virtual GoogleString net_instaweb::SharedMemCache< kBlockSize >::Name ( ) const

inlinevirtual

The name of this CacheInterface – used for logging and debugging.

It is strongly recommended that you provide a static GoogleString FormatName(...) method for use in formatting the Name() return, and in testing, e.g. in third_party/pagespeed/system/system_caches_test.cc.

Implements net_instaweb::CacheInterface.

template<size_t kBlockSize>

virtual void net_instaweb::SharedMemCache< kBlockSize >::Put	(	const GoogleString &	key,
		const SharedString &	value
	)

virtual

Puts a value into the cache. The value that is passed in is not modified, but the SharedString is passed by non-const pointer because its reference count is bumped.

Implements net_instaweb::CacheInterface.

template<size_t kBlockSize>

void net_instaweb::SharedMemCache< kBlockSize >::RegisterSnapshotFileCache	(	FileCache *	potential_file_cache,
		int	checkpoint_interval_sec
	)

Use the specified FileCache for loading and storing snapshots. This may be called multiple times with different FileCaches but we pick one. If the cache has the same path we were constructed with, use that. Otherwise, to handle the default shm cache case, use the cache with the path that comes first alphabetically.

template<size_t kBlockSize>

void net_instaweb::SharedMemCache< kBlockSize >::RestoreSnapshot ( const SharedMemCacheDump & dump )

Restores entries stored in the dump into this cache. The dump may contain multiple sectors.

template<size_t kBlockSize>

virtual void net_instaweb::SharedMemCache< kBlockSize >::ShutDown ( )

inlinevirtual

Stops all cache activity. Further Put/Delete calls will be dropped, and MultiGet/Get will call the callback with kNotFound immediately. Note there is no Enable(); once the cache is stopped it is stopped forever. This function is intended for use during process shutdown.

Todo:: TODO(morlovich): Implement

Implements net_instaweb::CacheInterface.

Member Data Documentation

template<size_t kBlockSize>

const int net_instaweb::SharedMemCache< kBlockSize >::kAssociativity = 4

static

Note: changing this requires changing

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

pagespeed/kernel/sharedmem/shared_mem_cache.h

Public Member Functions

Static Public Member Functions

Static Public Attributes

Additional Inherited Members

Detailed Description

template<size_t kBlockSize> class net_instaweb::SharedMemCache< kBlockSize >

Constructor & Destructor Documentation

Member Function Documentation

Member Data Documentation

template<size_t kBlockSize>
class net_instaweb::SharedMemCache< kBlockSize >