CachePolicy < Main

CachePolicy

Contents:

cache policy
- Description
NPL local server caching policy
- Member Functions

cache policy

Title	cache policy
Author(s)	LiXizhi
Date	2008/3/2
File	script/kids/3DMapSystemApp/localserver/cache_policy.lua

Description

In NPL local server, there is a single cache policy which is slight different from standard HTTP cache (The official version is here: http://www.w3.org/Protocols/rfc2616/rfc2616-sec14.html#sec14.9

)

NPL local server caching policy

The cache policy by NPL local server (and represented by this CachePolicy class) is stated below:

find the entry in the local server. If a completed entry is found, it is always returned immediately, regardless of whether it has expired or not.
if no entry is found or the entry expired, a new entry will be fetched via remote server and updated in the local server.
When a entry is updated in the store, it will be returned to all callback functions registered to it.

Note1: It means that the same request might be returned twice. The first time is the local version at the time of call; and the second time is when the entry is just updated via the server. The second call is skipped if the server can verify that the content has not changed and only update the last access time in the local store. Note2: If the relative expire time is 0, the first call is ignored. Note3: If the relative expire time is larger than a year, the second call is always ignored. Note4: This same policy applies to ResourceStore, ManagedResourceStore, and WebserviceStore.For WebserviceStore, only access base time type is permitted. The server policy can be overwritten by local server policy, local server policy can be overwritten by per function policy

To increase efficiency, one can create several different cache policy objects and share them for all local stores and related function calls.

Sample Code

NPL.load("(gl)script/kids/3DMapSystemApp/localserver/cache_policy.lua");
local cache_policy = Map3DSystem.localserver.CachePolicy:new("access plus 1 month");
cache_policy:IsExpired(ParaGlobal.GetSysDateTime()-80000);

-- there are some premade policies, which can be retrieve from Map3DSystem.localserver.CachePolicies, see below
local cp = Map3DSystem.localserver.CachePolicies["never"];
local cp = Map3DSystem.localserver.CachePolicies["always"];
local cp = Map3DSystem.localserver.CachePolicies["1 hour"];
local cp = Map3DSystem.localserver.CachePolicies["1 day"];

Member Functions

CachePolicy:new

--------------------------
 CachePolicy class
--------------------------

local CachePolicy = {
   -- The base time is either the last modification time of the file, or the time of the client's access to the document.
   -- 0 means that the file's last modification time should be used as the base time, 
   -- 1 means the client's access time should be used.
   -- nil Expiration is not enabled. 
   BaseTime = 1,
   -- Time in seconds to expire relative to BaseTime. e.g. 2592000 is a month, which is good for asset and images.  604800 is a week which is good for profile and content pages. 
   ExpireTime = 604800,
}

;

commonlib.setfield("Map3DSystem.localserver.CachePolicy", CachePolicy);

create the object and init from initCode. format of initCode, please see Init() function.

syntax

function CachePolicy:new(initCode)

parameters

initCode

CachePolicy:Init

[[ Extacts the policy base time type expire time from an input string.

param initCode : string: it has the following syntax

" [plus] { }*" where is one of: access, now (equivalent to 'access'), modification The plus keyword is optional should be an integer value, and is one of: years months weeks days hours minutes seconds For example, any of the following can be used to make entries expire 1 month after being accessed: - "access plus 1 month" - "access plus 4 weeks" - "access plus 30 days" The expiry time can be fine-tuned by adding several ' ' clauses: - "access plus 1 month 15 days 2 hours" - "modification plus 5 hours 3 minutes"

return __ : Returns true if successful.

]]

syntax

function CachePolicy:Init(initCode)

parameters

| initCode | string: it has the following syntax " [plus] { }*" where is one of: access, now (equivalent to 'access'), modification The plus keyword is optional should be an integer value, and is one of: years months weeks days hours minutes seconds For example, any of the following can be used to make entries expire 1 month after being accessed: - "access plus 1 month" - "access plus 4 weeks" - "access plus 30 days" The expiry time can be fine-tuned by adding several ' ' clauses: - "access plus 1 month 15 days 2 hours" - "modification plus 5 hours 3 minutes" |

CachePolicy:IsExpired

whether time is expired.

param Basetime : the base time in second
return __ : true if input time is expired

syntax

function CachePolicy:IsExpired(Basetime)

parameters

Basetime	the base time in second

CachePolicy:IsCacheEnabled

return whether : cache is enabled. i.e. self.ExpireTime is not 0.

syntax

function CachePolicy:IsCacheEnabled()

parameters

return	cache is enabled. i.e. self.ExpireTime is not 0.

CachePolicy:IsCacheAlwaysUsed

return whether : cache is always used. i.e. self.ExpireTime over 1 year.

syntax

function CachePolicy:IsCacheAlwaysUsed()

parameters

return	cache is always used. i.e. self.ExpireTime over 1 year.

Topic revision: r1 - 2008-02-29 - LiXizhi