Why don t I need CFLOCK with client variables in Java

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Why don t I need CFLOCK with client variables
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Session, Application, and Server variables are stored in memory and shared by multiple users, so access to them must be synchronized to prevent collision. Client variables are stored in a disk structure in either the Windows Registry, a database, or in a disk structure (cookie) on the client s machine. Access to these disk structures is inherently locked by the operating system (in the case of the Registry), the database server, or the host machine (in the case of a cookie), so no CFLOCK synchronization of the code that attempts to access and manipulate these structures is necessary.
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Nesting calls to CFLOCK
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Beware of nesting one call to CFLOCK inside another. Never, for example, do the following:
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<cflock scope= SESSION type= READONLY timeout= 60 > . . . <cflock scope= SESSION type= EXCLUSIVE timeout= 60 > . . .
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12 Understanding ColdFusion Variables
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</cflock> . . . </cflock>
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Spotting the error in this code may be difficult. The problem is that the code acquires a readonly lock of the Session scope and then attempts to acquire an exclusive lock of the same scope while it is still locked. This snippet of code leads to a condition called a deadlock, where your code is trying to acquire a second lock on a resource that it s already locked. The best way to avoid deadlock conditions is to do the following: 1. Put your calls to CFLOCK around only that code that absolutely must be synchronized with other code. 2. Never attempt to acquire a second lock on a scope while that scope is already locked. 3. Release locks in the reverse order in which they are acquired. Take, for example, the following code:
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<cflock scope= SESSION type= EXCLUSIVE timeout= 60 > . . . <cflock scope= APPLICATION type= EXCLUSIVE timeout= 60 > . . . <cflock scope= SERVER type= EXCLUSIVE timeout= 60 > . . . </cflock> </cflock> </cflock>
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This use of nested locks is valid here because you never attempt to acquire a second lock of the same scope until the first is released, and you also lock and release the smaller scopes before acquiring locks on the larger scopes.
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Testing for Variables
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One of the more often-used tags in ColdFusion is CFPARAM, which lets you do three things: Ensure that a variable exists, Give a variable a default if the variable doesn t exist, or Ensure that a variable is of a given type. The following snippet ensures that a variable named Form.MyFormField exists:
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<cfparam name= Form.MyFormField >
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When ColdFusion executes the preceding line, ColdFusion looks for a variable named Form.MyFormField. If the variable exists, ColdFusion will continue on with the next line of code. If Form.MyFormField does not exist, however, ColdFusion will throw an error. You will see in 18 how this helps ensure that custom tags are always used correctly. There are times when you may not want to throw an error if a variable doesn t exist. If Form.MyFormField were a checkbox, for example, you wouldn t want to throw an error of Form.MyFormField didn t exist; rather, you d want to automatically create Form.MyForm Field and give it a default of zero. (See 6 for information on using checkboxes in form fields.) The following snippet shows how to give Form.MyFormField a default:
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Part III The ColdFusion MX Language
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<cfparam name= Form.MyFormField default= 0 >
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Adding the default attribute tells ColdFusion to assign the default if Form.MyFormField doesn t already exist.
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CFPARAM will also allow you to check the type of an incoming variable, as in the following
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snippet:
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<cfparam name= Form.MyFormField type= numeric >
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The preceding line checks to see that Form.MyFormField exists, and also that it is a numeric value. If, for instance, the user had entered ABC into the form field, the preceding line of code would throw an error. Note that you can combine the type and default attributes together, as in the next snippet: