coldfusion how do I unlock code programatically - coldfusion

Question

In ColdFusion the cflock tag provides a timeout in seconds. My problem is that I want to unlock the code when certain other code is completed. For example, I have code that says:
<!---need some kind of lock here --->
<!---this code is in a loop --->
<cffile action = 'append'
file = '#path#'/temp.cfm'
output = '#myvariable#'>
Later in the program the temp file is picked up, to be combined with other information:
<cffile action = 'read'
file = '#path#/temp.cfm'
variable = 'xyz'>
But I can't guess how long it will take to get from the creation of temp to the reading of it. That may depend for example on the number of records in a MySql file, or could timeout because of slow traffic, or for other reasons.
So what I'd like to do is unlock temp after the read is completed. In other words, I'd like a cfunlock tag, but there doesn't seem to be one. Does anyone know how to do this?

Answer 1

The cflock timeout parameter does not specify how long the code can take to run, it specifies the time to wait for a lock to be provided before timing out. When the code inside your cflock block is complete, your cflock will be unlocked.

Answer 2

If the "Later in the program" read is actually later in the same single synchronous request as the original append/write, then you don't even need the lock, unless there is a risk of multiple concurrent requests.
If the read is in a separate request to the write, but you know the write will always start first, then you just need a type="exclusive" lock on the write and a type="readonly" lock on the read, using the same lock name, then the readonly lock will wait for the code in the exclusive lock to complete.
If your read might start before your write, and you know you need to wait for the first/next write state to be reached before the read would be valid, then that's when you would need to add some polling logic of your own to check whether the desired state has been reached before reading. There are many ways of achieving that - essentially after the write has completed, you could flag that state in an application variable or in your database, or rename the file after the write is complete, and then before your read code, check for the expected state in a loop and wait and check again until that state is reached, before continuing with the read.

Answer 3

The following solution requires no lock. It makes use of a persistent scope, for example, request, session or application. Choose the scope appropriate to your case.
<!--- Placed before the file-append code --->
<cfset session.isTempFileAppendComplete=false>
...
<!---this code is in a loop --->
<cffile action = 'append'
file = '#path#'/temp.cfm'
output = '#myvariable#'>
...
<!--- Placed after the file-append code --->
<cfset session.isTempFileAppendComplete=true>
<cfif session.isTempFileAppendComplete>
<cffile action = 'read'
file = '#path#/temp.cfm'
variable = 'xyz'>
</cfif>

Answer 4

If there are going to be multiple concurrent users, with the possibility of each having multiple concurrent requests, then use an application-scoped or a named lock. However, I assume a single concurrent user.
To avoid concurrent requests, add session locks (not named locks, as these are in application scope):
<cflock timeout = "10" scope = "session" type = "exclusive">
<cfset session.isTempFileAppendComplete=false>
</cflock>
...
<cflock timeout = "600" scope = "session" type = "exclusive"><!---decide on timeout estimate --->
<!---this code is in a loop --->
<cffile action = 'append'
file = '#path#'/temp.cfm'
output = '#myvariable#'>
</cflock>
...
<cflock timeout = "600" scope = "session" type = "exclusive">
<!--- Placed after the file-append code --->
<cfset session.isTempFileAppendComplete=true>
</cflock>
<cflock timeout = "60" scope = "session" type = "readOnly">
<cfif session.isTempFileAppendComplete>
<cffile action = 'read'
file = '#path#/temp.cfm'
variable = 'xyz'>
</cfif>
</cflock>