net_instaweb::PurgeContext Class Reference

#include "purge_context.h"

Public Types
typedef Callback2< bool, StringPiece >	PurgeCallback
typedef Callback1< const CopyOnWrite< PurgeSet > & >	PurgeSetCallback

Public Member Functions
	PurgeContext (StringPiece filename, FileSystem *file_system, Timer *timer, int max_bytes_in_cache, ThreadSystem *thread_system, NamedLockManager *lock_manager, Scheduler *scheduler, Statistics *statistics, MessageHandler *handler)
void	set_request_batching_delay_ms (int64 delay_ms)
void	AddPurgeUrl (StringPiece url, int64 timestamp_ms, PurgeCallback *callback)
void	SetCachePurgeGlobalTimestampMs (int64 timestamp_ms, PurgeCallback *callback)
void	PollFileSystem ()
void	SetUpdateCallback (PurgeSetCallback *cb)
void	set_enable_purge (bool x)

Static Public Member Functions
static void	InitStats (Statistics *statistics)

Static Public Attributes
static const int	kCheckCacheIntervalMs = 5 * Timer::kSecondMs
static const char	kCancellations []
	Variable names.
static const char	kContentions []
static const char	kFileParseFailures []
static const char	kFileStats []
static const char	kFileWriteFailures []
static const char	kFileWrites []
static const char	kPurgeIndex []
static const char	kPurgePollTimestampMs []
static const char	kStatCalls []

Friends
class	PurgeContextTest

Detailed Description

Handles purging of URLs, atomically persisting them to disk, allowing multiple concurrent threads/processes to handle purge requests and propagate them to the other processes.

All public methods in this class are thread-safe.

This class depends on Statistics being functional. If statistics are off, then cache purging may be slower, but it will still work.

Member Function Documentation

void net_instaweb::PurgeContext::AddPurgeUrl	(	StringPiece	url,
		int64	timestamp_ms,
		PurgeCallback *	callback
	)

Adds a URL to the purge-set, atomically updating the purge file, and transmitting the results to the system, attempting to do so within a bounded amount of time.

Calls callback(true, "") if the invalidation succeeded (was able to grab the global lock in a finite amount of time), and callback(false, "reason") if it failed. If we fail to take the lock then the invalidation is dropped on the floor, and statistics "purge_cancellations" is bumped.

void net_instaweb::PurgeContext::PollFileSystem

(

)

Periodically updates the purge-set from disk if enough time has expired. This can be called on every request.

void net_instaweb::PurgeContext::set_enable_purge ( bool  x )

inline

Indicates whether individual URL purging is supported. If false, then we only take the cache.flush file timestamp to do full cache flushes. If true, then we read and parse the contents of the file to find the global invalidation time and cache-flush times for the individual entries.

void net_instaweb::PurgeContext::set_request_batching_delay_ms ( int64  delay_ms )

inline

By default, PurgeContext will try to acquire the lock and write the cache.purge file as soon as it is called. This may present a significant load to the file system, causing delays.

In a multi-threaded or asynchronous environment (e.g. any environment other than Apache HTTPD pre-fork MPM), it is desirable to batch up requests for a time (e.g. 1 second) before writing the updated cache file.

void net_instaweb::PurgeContext::SetCachePurgeGlobalTimestampMs	(	int64	timestamp_ms,
		PurgeCallback *	callback
	)

Sets the global invalidation timestamp.

Calls callback(true, "") if the invalidation succeeded (was able to grab the global lock in a finite amount of time), and callback(false, "reason") if it failed. If we fail to take the lock then the invalidation is dropped on the floor, and statistics "purge_cancellations" is bumped.

void net_instaweb::PurgeContext::SetUpdateCallback

(

PurgeSetCallback *

cb

)

To test whether URLs are purged, you must capture a PurgeSet by registering a callback. The PurgeSet is passed to the callback using a CopyOnWrite wrapper so that the callback can efficiently share the storage.

IsValid calls can then be made using the PurgeSet captured by the callback.

Member Data Documentation

const int net_instaweb::PurgeContext::kCheckCacheIntervalMs = 5 * Timer::kSecondMs

static

The source-of-truth of the purge data is kept in files. These files are checked for changes via stat every 5 seconds.

Todo:

TODO(jmarantz): make this settable.

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

• pagespeed/kernel/cache/purge_context.h