Improve transient memory consumption of UIXComponentBase.getClientId()
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Key: TRINIDAD-1669
URL: https://issues.apache.org/jira/browse/TRINIDAD-1669
Project: MyFaces Trinidad
Issue Type: Improvement
Environment: All
Reporter: Blake Sullivan
Calling UIXComponentBase.getClientId consumes a great deal of transient memory.
Under light loads, this doesn't matter--the objects are extremely short-lived
and are allocated out of the first-generation heap. However, when large
numbers of users are accessing the server simultaneously these allocations
contribute to first-generation heap exhaustion and first-generation heap GC's
when deeply nested NamingContainers are used.
There are two reasons that large amounts of transient memory is consumed in
these cases:
1) UIXComponentBase doesn't cache clientIds because the clientIds are partly
determined by the component's ancestors and there are cases (such as stamping),
where multiple clientIds may map to a single component instance
2) clientIds are generated recursively by:
a) calling getContainerClientId() and appending the NamingContainer separator
and the component's id to the result
b) getContainerClientId() is implemented by calling getContainerClientId() and
doing likewise
So, each NamingContainer in the hierarchy is going to:
1) Get it's ancestor's container clientId and if one exists
2) Get it's id attribute
3) Allocate a StringBuilder to contain these two Strings, append them together
4) Convert the StringBuilder to a String and return the result
An earlier JIRA used a ThreadLocal StringBuilder to remove the StringBuilder
allocation in step 3) in the common case, halving the transient memory usage,
however we still have the String allocations made necessary by the use of
String getContainerClientId(FacesContext context, UIComponent child).
For a 20 row table containing 10 columns nested four NamingContainers deep
(counting the table as one of these), we end up with 1000 String allocations,
which wouldn't necessarily be that bad if the size of the Strings wasn't
increasing and if the Rendering code was the only code calling getClientId()
(InvokeOnComponent is the primary culprit here, though replacing
invokeOnComponent calls with visitTree calls improves things).
The proposed solution is to replace generating new Strings at each
NamingContainer level with appending the NamingContainer ids into a
StringBuilder (in fact, the shared StringBuilder) passed to the appending
code--a String is only generated when the returning the value from
getClientId(). In scalability testing, this change has been worth about 8%.
The advantages of this approach are:
1) If the component code compiles, the code will almost certainly work correctly
2) It clientId caching is also used, this approach speeds up generation of the
cached result
The disadvatanges of this approach is:
1) Any overrides of getClientId() or getContainerClientId() must be changed to
overrides of appendClientId() or appendContainerClientId(). To enforce this,
getClientId() and getContainerClientId() are made final on UIXComponentBase.
This, is of course, an incompatible api change
The new/changed apis on UIXComponentBase:
/**
* Appends the container's clientId for the requesting child to the
StringBuilder, returning the passed in StringBuilder.
* Component implementations are only allowed to mutate the StringBuilder
other than to append.
* Subclasses that wish to modify the clientIds returned for their children
should override this method rather than
* <code>getContainerClientId</code>.
* @param context FacesContext
* @param child Optional child component that is requesting the container's
* clientId
* @param clientIdAppendable StringBuilder to append the container's clientId
to
* @see #getContainerClientId(FacesContext, UIComponent)
*/
public StringBuilder appendContainerClientId(
FacesContext context,
UIComponent child,
StringBuilder clientIdAppendable)
/**
* Appends the clientId of this component to the StringBuilder, returning the
passed in StringBuilder.
* Component implementations typically only mutate the StringBuilder to
append.
* Subclasses that wish to modify the clientIds that they return should
override this method rather than
* <code>getClientId</code>.
* @param context FacesContext
* @param clientIdAppendable StringBuilder to append the component's clientId
to
* @return the clientIdAppendable StringBuilder passed in as the
clientIdAppendable parameter
* @see #getClientId
*/
public StringBuilder appendClientId(FacesContext context, StringBuilder
clientIdAppendable)
/**
* Final override of getContainerClientId to make
<code>appendContainerClientId</code>
* the supported hook for modifying the clientIds of a component's children.
* @see #appendContainerClientId
*/
@Override
public String getContainerClientId(FacesContext context)
/**
* Final override of getContainerClientId to make
<code>appendContainerClientId</code>
* the supported hook for modifying the clientIds of a component's children.
* The implementation uses <code>appendContainerClientId</code> to calculate
the
* the container's clientId prefix with far fewer temporary Strings than
* the class JSF implementation.
* @param context FacesContext
* @param child Optional child component that is requesting the container's
* clientId
* @return the clientId prefix to add to the child's id
* @see #appendContainerClientId
*/
@Override
public final String getContainerClientId(FacesContext context, UIComponent
child)
/**
* Final override of getClientId to make <code>appendClientId</code>
* the supported hook for modifying the clientIds of a component.
* The implementation uses <code>appendClientId</code> to calculate the
* the component's clientId with far fewer temporary Strings than
* the class JSF implementation.
* @param context FacesContext
* @return the clientId
* @see #appendClientId
*/
@Override
public final String getClientId(FacesContext context)
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