Re: Is Adding EOAttribute to EOEntity Thread Safe?
Re: Is Adding EOAttribute to EOEntity Thread Safe?
- Subject: Re: Is Adding EOAttribute to EOEntity Thread Safe?
- From: Chuck Hill <email@hidden>
- Date: Mon, 31 Mar 2008 14:25:06 -0700
EOF is single threaded at this level. So the threads just wait for
the lock. If you have mis-matched locks (e.g. lock the db context but
never unlock it), the app just deadlocks. No timeout, no exception.
Just a warm, fuzzy deadlock. try... finally is your friend.
Chuck
On Mar 31, 2008, at 2:21 PM, Dov Rosenberg wrote:
Is there a queue where requests get stored in or some sort of timeout
waiting for the lock to release? Or is the failure an outright
exception?
Dov Rosenberg
On 3/31/08 4:25 PM, "Chuck Hill" <email@hidden> wrote:
On Mar 31, 2008, at 1:15 PM, Dov Rosenberg wrote:
I guess the real problem is trying to run multithreaded apps
against a
single threaded EOF stack. Unless we start using multiple EOF stacks
we
could potentially have other performance problems lurking in the
shadows
More likely from slow fetches and repeated tripping of single faults
than this. If you are doing lot of these counts, it would make sense
to create a separate EOF stack just for them.
Chuck
On 3/31/08 3:39 PM, "Chuck Hill" <email@hidden> wrote:
That is how you lock the EOF stack. While the stack is locked, no
other thread can fetch / save. This same lock happens during all
fetch or save operations.
Chuck
On Mar 31, 2008, at 12:09 PM, Dov Rosenberg wrote:
Taking a look at the new code – I agree it looks a bit safer than
the old code. What is the implication for doing an
EODatabaseContext
lock in a multi threaded app? Will that cause any problems if
multiple sessions are trying to do something similar concurrently?
Dov Rosenberg
On 3/30/08 5:56 PM, "Mike Schrag" <email@hidden> wrote:
It's not thread safe, and Wonder's implementation doesn't
actually
work like this anymore (your code is based on a version from last
year sometime) ... See
ERXEOControlUtilities._aggregateFunctionWithQualifier for an
example of how to do it properly (we actually create an attribute
without adding it to the entity)
ms
On Mar 30, 2008, at 5:43 PM, Dov Rosenberg wrote:
We have some code that we are using from Project Wonder (I
think)
that adds an attribute programmatically to an EOEntity to do
things like count, max, etc. (See below). We were doing a load
test on our application and started throwing errors because a
different query was submitted using the extra attribute. It
seems
that making changes to the EOModel is not thread safe. If that
is
the case is there anything we can do to use this code? Or should
we dump this and build a regular fetch for the aggregate data.
Any
thooughts or insights would be a huge help.
Query that was generated in error – notice the COUNT() attribute
embedded in the query incorrectly
"SELECT t0.ACTUALRATING, t0.BODY, t0.CLOSED, t0.DATEADDED,
t0.DATEMODIFIED, t0.FORUMID, t0.IPADDRESS, t0.LOCALEID,
t0.MODERATE, COUNT(t0.RECORDID), t0.PUBLISHED, t0.RECORDID,
t0.STATUS, t0.TITLE, t0.TYPE, t0.USERID, t0.USERNAME,
t0.USERNICKNAME, t0.WEIGHTEDRATING FROM DBTOPIC t0 WHERE
t0.RECORDID = ?" withBindings:
1:"0032274bc94901122623a943007f46"(recordID)>:
Next exception:SQL State:42000 -- error code: 937 -- msg:
ORA-00937: not a single-group group function
This is the code that we use to add the temporary attribute.
public static Number
aggregateNumberFunctionWithQualifier(EOEditingContext ec, String
entityName, String attributeName, String function, EOQualifier
qualifier) { EOEntity entity =
EOUtilities.entityNamed(ec,
entityName); NSArray results = null; EOAttribute
attribute = createAggregateAttribute(ec, function,
attributeName,
entityName, "java.lang.Number", "i"); EOQualifier
schemaBasedQualifier =
entity.schemaBasedQualifier(qualifier);
EOFetchSpecification fs = new EOFetchSpecification(entityName,
schemaBasedQualifier, null); synchronized (entity)
{ entity.addAttribute(attribute);
try{ fs.setFetchesRawRows(true);
fs.setRawRowKeyPaths(new
NSArray(attribute.name())); results =
ec
.objectsWithFetchSpecification
(fs
); }finally
{ entity
.removeAttribute(attribute); } } if
((results != null) && (results.count() == 1))
{ NSDictionary row = (NSDictionary)
results.lastObject(); if
(row.objectForKey(attribute.name()) != null &&
row.objectForKey(attribute.name()) instanceof Number)
{ return (Number)
row.objectForKey(attribute.name()); } }
return null; }
Dov Rosenberg
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