Andrew Robinson said the following On 1/4/2010 2:38 PM PT:
Andrew,
Thanks for commenting on this.
Why isn't UIXComponentBase caching the client ID?
Because of stamping and because I suspect that FacesBean would have
complicated things.
The JSF core
components already cache their client ID. Part of the spec. is that
setId() calls on the component clear the cache.
Can you point me to the section, where it says this? This behavior is
not part of section 3.1.6 of the JSF 2.0 Specification (which is wrong
anyway, as the behavior it describes would preclude the stamping
implemented by UIData. And is it just me or do others think that it is
backwards that the specification would actually tell the reader to look
in the javadoc to find out what the specified behavior is?)
In Trinidad, we must
recursively call setId on child components when indexes change
(tr:iterator, tr:table, etc.) so that JSF components function
correctly.
I believe this is an JSF RI implementation detail. I see nothing in the
specification that says that calling setId() will clear out the current
clientId even if the passed in id is identical to the component's
current id. This behavior is also not exactly performant as each row
change for any reason requires a walk of the row subtree to clear out
the clientIds.
Since we already have to do the work of clearing the cached
client IDs for JSF components, can we not take advantage of this for
Trinidad components? I would think that this would be a large
performance improvement.
We if we put in JIRA-1668--Speed up UIXComponent.getId(), we could,
since that JIRA solves the problem of how to add programmatic logic to
get/setId() as a side-effect. The issues then would be quality and some
performance. The quality part would be double-checking that the
StampState class (which implements the setId resetting behavior) is
being used correctly in all cases (since we would only notice right now
if non UIComponents were used) and checking whether we will have
problems with tag implementations that bogusly call getClientId().
The two mechanisms are complimentary, but I would prefer not to make the
api change if the caching change is good enough.
-- Blake Sullivan
Do you feel that your proposed changes would give us better
performance, or perhaps could we combine the two?
-Andrew
On Thu, Dec 31, 2009 at 4:23 PM, Blake Sullivan
<blake.sulli...@oracle.com> wrote:
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)
