Oh, I thought it was clear from my e-mail that I know how the RI
implements setClientId(). Note that the RI implementation isn't really
compatible with the spec language. The UIData doesn't change the
children id attributes in any Java sense of the word (precisely the same
instance is used). In fact, the id portion of the current spec language
comes from Adam Winer and his javadoc updates were submitted without
knowing the details of the just checked-in UIData component. Craig
McClanahan made the change to add clientId caching at the same time he
added the UIData implementation. There was no EG discussion of Craig's
setId() hack. In fact, the check-in comments make clear that the
clientId was cached in order to (incorrectly) fix the problem JSF was
having that if the id attribute wasn't set, each call to getClientId()
would return a different value.
As for the JavaDoc--of course it is normative--it just seems a little
odd to make the specification and the JavaDoc mutually dependent when
there is no need to do so.
Now it is completely fair to argue that we are stuck with the bogus RI
cache-clearing implementation detail anyway, so we might as well embrace
it, which is why I laid out the steps we would need to take to correctly
implement the caching. Do you have any comments on those?
-- Blake Sullivan
Andrew Robinson said the following On 1/4/2010 8:08 PM PT:
The JavaDoc is part of the spec, and according to JSF 1.2, the
getClientId has this restriction (see http://goo.gl/eula):
"The return from this method must be the same value throughout the
lifetime of the instance, unless the id property of the component is
changed, or the component is placed in a NamingContainer whose client
ID changes (for example, UIData). However, even in these cases,
consecutive calls to this method must always return the same value"
As mentioned here, the client ID must not change unless someone
changes the ID property of the component, the clause of the UIData
does not mention how it should be updated though.
Now the hack? that JSF uses can be seen here:
http://kickjava.com/src/javax/faces/component/UIData.java.htm
Look at the getInitialClientId method.
Now looking at the UIComponentBase.java you can see that it caches the
client ID as a member variable in getClientId:
http://goo.gl/bNn1
You can also see in that source they set the client ID to null in setId(String)
Now look at the code for UIData.java:
http://goo.gl/1zCC
There is this:
private void restoreDescendantState(UIComponent component,
FacesContext context) {
// Reset the client identifier for this component
String id = component.getId();
component.setId(id); // Forces client id to be reset
Looking at the MyFaces core source code for UIData.java (jsf 1.2):
http://goo.gl/1d7j
It says this:
// reset the client id (see spec 3.1.6)
component.setId(component.getId());
At the end of 3.1.6 of the JSF 1.2 spec is this:
"The value returned from this method must be the same throughout
the lifetime of the component instance unless setId() is called, in
which case it will be
recalculated by the next call to getClientId()."
So, according to this, the caching that JSF core does is okay per this
spec. and Trinidad is actually incorrect in that its client IDs may
change without setId() being called. Not very intuitive or easy to
find, but it is there.
I happen to know about this as I had to fix a bug in the Trinidad
Table component because JSF component's setId() functions were not
being called and therefore the client IDs were all wrong, otherwise I
would have had no idea this was true.
-Andrew
On Mon, Jan 4, 2010 at 5:37 PM, Blake Sullivan
<blake.sulli...@oracle.com> wrote:
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)
