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Public Member Functions | Protected Member Functions
net_instaweb::AsyncFetchWithLock Class Reference

#include "async_fetch_with_lock.h"

Inheritance diagram for net_instaweb::AsyncFetchWithLock:
net_instaweb::AsyncFetch

List of all members.

Public Member Functions

 AsyncFetchWithLock (const Hasher *hasher, const RequestContextPtr &request_context, const GoogleString &url, const GoogleString &cache_key, NamedLockManager *lock_manager, MessageHandler *message_handler)
bool Start (UrlAsyncFetcher *fetcher)
const GoogleString & url () const
 Url to be fetched.
const GoogleString & cache_key () const
 Cache key to be locked.

Protected Member Functions

virtual bool ShouldYieldToRedundantFetchInProgress ()=0
virtual void Finalize (bool lock_failure, bool success)
virtual bool StartFetch (UrlAsyncFetcher *fetcher, MessageHandler *handler)=0
virtual void HandleDone (bool success)
virtual void HandleHeadersComplete ()
virtual bool HandleWrite (const StringPiece &content, MessageHandler *handler)
virtual bool HandleFlush (MessageHandler *handler)

Detailed Description

AsyncFetch object which tries to acquire lock before fetching content. Start() will returns false, if it fails to acquire lock. Note that acquiring a lock will fail if same resource is fetching somewhere else. Caller will call the Start() which will try to acquire a lock and internally call StartFetch() which actually triggers a fetch. Sequence of the events: 1) Caller calls AsyncFetchWithLock::Start(). 2) Start() will try to acquire lock. If lock is acquired successfully, AsyncFetchWithLock::StartFetch() will be called, otherwise AsyncFetchWithLock::Finalize() is called with lock_failure as true and success as false and StartFetch() returns false and async_fetch_with_lock object will be deleted. Note: StartFetch() will be called in case of lock failure only if ShouldYieldToRedundantFetchInProgress() returns false. 3) Subclass defines StartFetch() function which actually triggers UrlAsyncFetcher::Fetch(). 4) Subclass can override HandleHeadersComplete(), HandleWrite(), HandleFlush() and HandleDone() for special handling during fetch. HandleDone() also releases the lock. Note: If any of these functions is overridden, then AsyncFetchWithLock::HandleXXX should also be called. 5) Lastly AsyncFetchWithLock::Finalize() is called just before async_fetch delete itself.


Member Function Documentation

virtual void net_instaweb::AsyncFetchWithLock::Finalize ( bool  lock_failure,
bool  success 
) [protected, virtual]

Finalize is called either when we fail to acquire acquire a lock or at the end of request after releasing the lock.

virtual void net_instaweb::AsyncFetchWithLock::HandleDone ( bool  success) [protected, virtual]

Releases the lock. If subclass overrides the function, then, it should also call AsyncFetchWithLock::HandleDone()

Implements net_instaweb::AsyncFetch.

virtual void net_instaweb::AsyncFetchWithLock::HandleHeadersComplete ( ) [protected, virtual]

HandleHeadersComplete(), HandleWrite() and HandleFlush() are no-op functions and any special handling can be done in subclass and must call the superclass function before returning.

Implements net_instaweb::AsyncFetch.

If someone is already fetching this resource, should we yield to them and try again later? If so, return true. Otherwise, if we must fetch the resource regardless, return false.

This will first try to acquire lock and triggers fetch by calling StartFetch() if successful. Returns false, if it fails to acquire lock and deletes this.

virtual bool net_instaweb::AsyncFetchWithLock::StartFetch ( UrlAsyncFetcher fetcher,
MessageHandler *  handler 
) [protected, pure virtual]

StartFetch() will be called after the lock is acquired. The subclass implements this function and is responsible for UrlAsyncFetcher::Fetch().


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