OJVM bug ??

Hi,
I found some discrepency on the results shown by memory profiler of JDEV (9.0.2) and that of NetBeans (IDE 4.0). Also, results of JDEV profiler is in contradiction to what Sun Java says (as per my own interpretation!). Here is what I am trying to do -
1. Loading classes dynamically using a custom classloader.
2. Once usage of the dynamically loaded class is finished, I am setting the classloader reference to null, so that next time the classloader loads the class afresh.
The code is working fine as per as loading the classes dynamically is concerned. However, while debugging in jdev, I monitored the classes being loaded and the heap size. This showed that the classloader is not being unloaded from memory and the count and size are increasing. The reference path of each of the classloader shows that the reference is being held by the class loaded by the classloader. This goes into a loop as Sun java says that to unload a class from memory, the classloader needs to be unloaded. I was using OJVM with java version - 1.3.1_02
When I tested the same code with NetBeans memory profiler it showed that the count of classloader objects increasing with every instantiation, but the number of live objects in memory is zero. The NetBean IDE was using Java 1.4.2_07.
Could this be a problem of -
1. My interpretation.
2. Java version (1.3.1_02) of OJVM that I am using.
3. Jdeveloper.
Would appreciate any help in this regard.
Thanks in advance
Indranil

Yes, this is an JVM optimizer bug. Thanks for reporting it, we didn't know about it. We will fix it for 9.0.4 and subsequent releases. In the mean time, you have two options:
1 - Run your application with the following addtional
JVM option -XOd
2 - Run your application with -client jvm
Michel

Similar Messages

BUG: Unable to increase stack size in OJVM

Hi,
I have a complex ADF Faces page (jspx) that has reached the level of complexity that I can reliably cause the JVM to die when running the page with:
Fatal error: Cannot find class java/lang/StackOverflowError
Process exited with exit code -1.when running within JDeveloper. I have tried adding
-Xms1024m -Xmx1024m(yes, I know an outrageous stack size) to the project run properties, and it still crashes. However, if I change to the server JVM instead of ojvm, it works fine, even with a much smaller stack, although the default stack size will crash as well.
So,
1). Shouldn't -Xms and -Xmx work for OJVM? If not, this is going to be a pain when I need to debug, as OJVM rocks for that.
2). Is there some way to configure ADF/OC4J so that I won't bomb like this? I'm guessing that the XML document (JSPX) is big enough that it's causing the XML parser to blow up. Just a guess however.
Thanks,
John

It's unclear if the problems discussed happen after OJC compiles, or Javac compiles, or both. We have uncovered a bug in the compilation of jspx files using OJC. There is a chance that this bug fix will fix the problems mentioned. Email me at keimpe.bronkhorst AT oracle.com if you want to try out a patched OJC. This is not an OJVM fix, so if you compile with Javac, I can't help you at this time.
Keimpe Bronkhorst
JDev team

Bug on native code of OJVM java.util.zip.CRC32.updateBytes(CRC32.java)

I want to unzip OpenOffice 1.0 files inside the OJVM but it fails into the native method java.util.zip.CRC32.updateBytes(CRC32.java).
The first execution of the code runs OK, but the second not.
After a long wait it shutdown the connection and the oracle trace file shows an stack trace like this:
*** 2003-04-18 11:31:31.926
*** SESSION ID:(17.97) 2003-04-18 11:31:31.926
java.lang.IllegalArgumentException
at java.util.zip.CRC32.updateBytes(CRC32.java)
at java.util.zip.CRC32.update(CRC32.java)
at java.util.zip.ZipInputStream.read(ZipInputStream.java)
at oracle.xml.parser.v2.XMLByteReader.fillByteBuffer(XMLByteReader.java:354)
at oracle.xml.parser.v2.XMLUTF8Reader.fillBuffer(XMLUTF8Reader.java:142)
at oracle.xml.parser.v2.XMLByteReader.saveBuffer(XMLByteReader.java:448)
at oracle.xml.parser.v2.XMLReader.fillBuffer(XMLReader.java:2012)
at oracle.xml.parser.v2.XMLReader.skipWhiteSpace(XMLReader.java:1800)
at oracle.xml.parser.v2.NonValidatingParser.parseMisc(NonValidatingParser.java:305)
at oracle.xml.parser.v2.NonValidatingParser.parseProlog(NonValidatingParser.java:274)
at oracle.xml.parser.v2.NonValidatingParser.parseDocument(NonValidatingParser.java:254)
at oracle.xml.parser.v2.XMLParser.parse(XMLParser.java:225)
at com.prism.cms.frontend.EditPropertiesActions.processUpload(EditPropertiesActions.java:1901)
Exception signal: 11 (SIGSEGV), code: 1 (Address not mapped to object), addr: 0x6d3a74a0, PC: [0x40263600, eomake_reference_to_eobjec
t()+80]
Registers:
%eax: 0x54a54000 %ebx: 0x40429c20 %ecx: 0x54a546bf
%edx: 0x6d3a7478 %edi: 0x402b27d0 %esi: 0x45c718ac
%esp: 0xbfffbf20 %ebp: 0xbfffbf48 %eip: 0x40263600
%efl: 0x00010206
The code of the java method is:
public static void processUpload(String id_page, String longname,
String filename, String filetype,
String s00)
throws SQLException {
Integer p_id = new Integer(id_page);
String toSource;
XMLDocument doc = null;
DOMParser theParser = null;
InputStream XSLStream = null;
BufferedWriter out = null;
#sql { select path||name||'.html' into :toSource from pages where id_page=:p_id };
if ("Cancel".equalsIgnoreCase(s00)) {
Jxtp.redirecUrl("/dbprism/ldoc/live/edit.html?p_source="+toSource);
return;
if ("no-file".equals(filename) && "no-contenttpye".equals(filetype)) {
Jxtp.redirecUrl("/dbprism/ldoc/live/edit.html?p_source="+toSource);
return;
if ("xml".equalsIgnoreCase(filetype))
#sql { call CMSj.moveFromUpload(:filename,:p_id) };
else if ("sxw".equalsIgnoreCase(filetype)) {
XSLProcessor processor = new XSLProcessor();
XSLStylesheet theXSLStylesheet = null;
BLOB locator = null;
// open sxw file, it will be in zip format with a file named content.xml
// then convert content.xml to document-v10.dtd with an stylesheet
#sql { select blob_content into :locator from wpg_document where name = :filename for update };
ZipInputStream zin = new ZipInputStream(locator.binaryStreamValue());
ZipEntry entry;
try {
while((entry=zin.getNextEntry())!=null)
if ("content.xml".equalsIgnoreCase(entry.getName())) {
Integer newVersion;
CLOB dstDoc;
CMSDocURLStreamHandlerFactory.enableCMSDocURLs();
try {
URL inUrl = new URL("cms:/stylesheets/sxw2document-v10.xsl");
XSLStream = inUrl.openStream();
// Create the Stylesheet from the stream
theXSLStylesheet = processor.newXSLStylesheet(XSLStream);
// Stores the document processing it with the given stylesheet
theParser = new DOMParser();
theParser.setValidationMode(theParser.NONVALIDATING);
theParser.setBaseURL(new URL("cms:/dtd/"));
theParser.parse(zin);
doc = theParser.getDocument();
#sql { SELECT NVL(MAX(version),0)+1 INTO :newVersion FROM content
WHERE cn_id_page = :p_id };
#sql { INSERT INTO content( cn_id_page, version, owner, status, source_file,
file_size, content, created, modified, created_by,
modified_by)
VALUES ( :p_id, :newVersion, sys_context('cms_context','user_id'),
'Uploaded', :filename, 0 , EMPTY_CLOB(), SYSDATE, SYSDATE,
sys_context('cms_context','user_id'),
sys_context('cms_context','user_id')) };
#sql { SELECT content INTO :dstDoc FROM content
WHERE cn_id_page = :p_id AND version = :newVersion for update };
#sql { call DBMS_LOB.trim(:inout dstDoc,0) };
out = new BufferedWriter(dstDoc.getCharacterOutputStream(),dstDoc.getChunkSize());
processor.processXSL(theXSLStylesheet, doc, new PrintWriter(out));
#sql { delete from wpg_document where name=:filename };
} catch (SAXParseException spe) {
throw new SQLException("processUpload SAXParseException: "+xmlError(spe));
} catch (SAXException se) {
throw new SQLException("processUpload SAXException: "+se.getLocalizedMessage());
} catch (XSLException xsle) {
throw new SQLException("processUpload XSLException: "+xsle.getLocalizedMessage());
} finally {
if (XSLStream!=null)
XSLStream.close();
if (theParser!=null)
theParser = null;
if (out!=null) {
out.flush();
out.close();
zin.close();
} catch (IOException ioe) {
throw new SQLException("processUpload IOException: "+ioe.getLocalizedMessage());
} finally {
if (XSLStream!=null)
XSLStream = null;
if (out!=null)
out = null;
if (zin!=null)
zin = null;
Jxtp.redirecUrl("/dbprism/ldoc/live/edit.html?p_source="+toSource);
Basically it takes the content from a BLOB column of the wpg_document table, unzip it using java.util.zip package, look for the file content.xml and parse it using Oracle XML toolkit.
Using an open source utility which replace java.util.package (http://jazzlib.sourceforge.net/) it works perfect because is a pure java application.
Best regards, Marcelo.
PD: I am using Oracle 9.2.0.2 on Linux.

The cause of errors was a dying Westen Digital drive, specially the 48G partition reserved only for $ORACLE_BASE (/dev/sdb3 mounted on /opt/oracle).
A simple quick scan of unmounted partition (badblocks -v /dev/sdb3) reported more than thousand new bad blocks (compared to the last scan six months ago). Although I strongly believe, specially in the case of WDC drives, that the best utility to "repair" bad blocks is the one that opens a window and prints the message: "Go to the nearest shop and buy a new drive", I was very curious to prove my suspicion just on this drive. After zero-filling the partition with dd, then formatting it (mke2fs -cc) and mounting again, the 11g installation and database creation (on the same partition) successfully completed, performing fast and smoothly. To make sure it was not a casual event, I repeated the installation once again with full success. The database itself is working fine (by now). Well, the whole procedure took me more than four hours, but I'm pretty satisfied. I learned once again - stay away from Western Digital. As Oracle cannot rely on dying drive, my friend is going tomorrow to spend a 150+ euro on two 250G Seagate Barracudas and replace both WDC drives, even though the first drive seems to be healthy.
In general there is no difference between loading correct data from good disk into bad memory and loading the incorrect data from dying disk into good memory. In both cases the pattern is damaged. For everyone who runs into the problem similar to this, and the cause cannot be easily determined, the rule of thumb must be:
1. test memory and, if it shows any error, check sockets and test memory modules individually
2. check disks for bad blocks regardless of the result of memory testing
Therefore I consider your answer being generally correct.
Regards
NJ

BUG OJVM does not work with tag files

Hello,
A.
1. Create tag file
2. Create JSP that uses tag file <x:xy />
3. Deploy to OC4J 10.1.3.2.
4. Start OC4J.
4. Access JSP - OK.
B.
1. Create tag file
2. Create JSP that uses tag file <x:xy />
3. Deploy to OC4J 10.1.3.2.
4. Start OC4J with OJVM.
4. Access JSP - OK.
C.
1. Create tag file
2. Create JSP that uses tag file <x:xy> </x:xy>
3. Deploy to OC4J 10.1.3.2.
4. Start OC4J with OJVM.
4. Error - the JSP cannot be displayed. No message.

user519938,
Am I missing something?
B and C look identical to me.
A and D also look identical to me.
By the way, can you not count above 4?
Good Luck,
Avi.

HAPPY BIRTHDAY, BUG 3169222!!

Dear Bug 3169222,
today is your second birthday and I wish you a happy one!
We created you two years ago. Since then, you cost us a lot of time and money, it's true, it' true. We created memory leaks and we had to buy profiling software since we cannot use the OJVM because of you.
However, we simply cannot imagine a JDeveloper version without you.
Oracle decided to fix you in a version after JDeveloper 12, so you can rest easy.
We will have many more years together, and many more birthdays to celebrate.
All the best from all of us here.
Sascha

And probably one of the reason it is in this state is
that there is no test-case that allows us to
reproduce.We uploaded a test case alright. I cannot tell you the TAR number, since I cannot search for TARs older than 365 days. If we had not provided a test case, it would not be a bug, wouldn't it. Oracle Support just lets those TARs bounce as we all know.
The bug not only applies to JIntegra btw, it also affects software modules running other JNI-using software (like our Morena TWAIN library). Probably it's the combination of JNI and obfuscated Java libraries that OJVM cannot handle.
Sascha
Message was edited by:
Sascha Herrmann

Jdeveloper 10g ojvm changing defaultCenturyStart

I have an application that runs fine using the java 1.4.1_05 jvm (hotspot or server) but when I run it using the 10g ojvm, after I execute the first prepartes statement, all my java.util.date objects go really strange.
Here is the code I am using to trace the problem.
protected static SimpleDateFormat s_dateFormat = new SimpleDateFormat("MM-dd-yyyy HH:mm:ss.SSS ");
Date newDate = Calendar.getInstance().getTime();
String preDateTime = s_dateFormat.toPattern() + " | " +
s_dateFormat.get2DigitYearStart() + " | " +
s_dateFormat.format(newDate) + " " + newDate.toString() +
" " + s_dateFormat.toLocalizedPattern();
The output looks like
MM-dd-yyyy HH:mm:ss.SSS | Mon Dec 03 16:35:23 EST 1923 | 12-03-2003 16:35:31.531 Wed Dec 03 16:35:31 EST 2003 MM-dd-yyyy HH:mm:ss.SSS
but then when I execute my first prepared statement, the same method starts outputing
MM-dd-yyyy HH:mm:ss.SSS | Wed Dec 02 21:16:41 EST 230747998 | 11-05-232044683 05:59:13.030 Mon Nov 05 05:59:13 EST 232044683 MM-dd-yyyy HH:mm:ss.SSS
MM-dd-yyyy HH:mm:ss.SSS | Wed Dec 02 21:16:41 EST 230747998 | 08-18-232078099 16:34:27.231 Tue Aug 18 16:34:27 EDT 232078099 MM-dd-yyyy HH:mm:ss.SSS
MM-dd-yyyy HH:mm:ss.SSS | Wed Dec 02 21:16:41 EST 230747998 | 05-10-232078243 17:38:51.807 Wed May 10 17:38:51 EDT 232078243 MM-dd-yyyy HH:mm:ss.SSS
so the s_dateFormat.get2DigitYearStart() is now 230747998?
If I tell 10g to use any other jvm, the times are ok.
Does the ojvm try to syncronize the database time and the system time or something weird like that?
Looks like a bug to me, wasn't sure where to post that.

Actually let me refine my answer. With the examples I tried it doesn't reproduce. If you could post a complete example that fails for you, I can give that a try as well.
Thanks again,
Herbert.

BUG ? - Problems with debugger

Hi,
I am trying to debug my application and put a break-point in one class that belongs to a different package and is filed in an directory that does not belong to this application. The fact is that this breakpoint is being ignored. It seems to be a bug.
Regards.
Fabio

I've a problem similar to this that solved using ojvm instead client.
To configure this Rigth Click i you project -> Project Properties -> Runner -> Choose ojvm in Virtual Machine list.
Best regards

Will you ever fix the BUG n. 5207902 ?

Hi,
I would like to know if Oracle intents to fix bug n. 5207902.
My problem: I cannot debug JSP that is deployed to standalone OC4J - or is it possible?
Branislav

Yes you can debug on a remote OC4J Container.
On the start command you need to include the debug settings
-XXdebug,port4000,detached,quiet
i.e.:
java -ojvm -XXdebug,port4000,detached,quiet - jar oc4j.jar
So in this case port 4000 is the one you can remotely debug to.

Index with "or" clause (BUG still exists?)

The change log for 2.3.10 mentions "Fixed a bug that caused incorrect query plans to be generated for predicates that used the "or" operator in conjunction with indexes [#15328]."
But looks like the Bug still exists.
I am listing the steps to-repro. Let me know if i have missed something (or if the bug needs to be fixed)
DATA
dbxml> openContainer test.dbxml
dbxml> getDocuments
2 documents found
dbxml> print
<node><value>a</value></node>
<node><value>b</value></node>
INDEX (just one string equality index on node "value")
dbxml> listIndexes
Index: unique-node-metadata-equality-string for node {http://www.sleepycat.com/2002/dbxml}:name
Index: node-element-equality-string for node {}:value
2 indexes found.
QUERY
setVerbose 2 2
preload test.dbxml
query 'let $temp := fn:compare("test", "test") = 0
let $results := for $i in collection("test.dbxml")
where ($temp or $i/node[value = ("a")])
return $i
return <out>{$temp}{$results}</out>'
When $temp is true i expected the result set to contain both the records, but that was not the case with the index. It works well when there is no index!
Result WITH INDEX
dbxml> print
<out>true<node><value>a</value></node></out>
Result WITHOUT INDEX
dbxml> print
<out>true<node><value>a</value></node><node><value>b</value></node></out>

Hi Vijay,
This is a completely different bug, relating to predicate expressions that do not examine nodes. Please try the following patch, to see if it fixes this bug for you:
--- dbxml-2.3.10-original/dbxml/src/dbxml/optimizer/QueryPlanGenerator.cpp     2007-04-18 10:05:24.000000000 +0100
+++ dbxml-2.3.10/dbxml/src/dbxml/optimizer/QueryPlanGenerator.cpp     2007-08-08 11:32:10.000000000 +0100
@@ -1566,11 +1572,12 @@
     else if(name == Or::name) {
          UnionQP *unionOp = new (&memMgr_) UnionQP(&memMgr_);
+          result.operation = unionOp;
          for(VectorOfASTNodes::iterator i = args.begin(); i != args.end(); ++i) {
               PathResult ret = generate(*i, ids);
               unionOp->addArg(ret.operation);
+               if(ret.operation == 0) result.operation = 0;
-          result.operation = unionOp;
     // These operators use the presence of the node arguments, not their valueJohn

Bug report follow-up

is there a way to follow-up on a bug report that i submitted? i have the bug number, but would like to see if the report was understood, filled out properly and determine the status of the bug report.
thanks,
doug

They comment on bugs if actions were taken. Otherwise - don't expect any feedback.

Solaris8 and 9 (possibly 7) /dev/poll driver bug report.

Hello,
I'd like to report a bug in the solaris 8 and 9 /dev/poll driver (poll(7d)).
As i do not have a support account with sun or anything like that, there
seems to be no other way to do that here (which is of course a very sad
thing).
Bug details:
The /dev/poll device provides an ioctl-request (DP_ISPOLLED) for checking
if a particular filedescriptor is currently in the set of monitored
filedescriptors for that particular /dev/poll fd set (open /dev/poll fd).
A quote from the documentation of the poll(7d) manual page taken from
Solaris9:
"DP_ISPOLLED ioctl allows you to query if a file descriptor is already in
the monitored set represented by fd. The fd field of the pollfd structure
indicates the file descriptor of interest. The DP_ISPOLLED ioctl returns 1
if the file descriptor is in the set. The events field contains the
currently polled events. The revents field contains 0. The ioctl returns 0
if the file descriptor is not in the set. The pollfd structure pointed by
pfd is not modified. The ioctl returns a -1 if the call fails."
It says that when you query for an filedescriptor which is currently being
monitored in the set, that it would return 1, and change the events field of
the pollfd structure to the events it's currently monitoring that fd for.
The revents field would be set to zero.
However the only thing which actually happens here, is that FD_ISPOLLED
returns 1 when the fd is in the set and 0 if not. When the fd is in the
set, when FD_ISPOLLED returns 1, the events field remains unmodified, but
the revents field gets changed.
A small sample code to illustrate:
#include <stdio.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <sys/devpoll.h>
main() {
struct pollfd a;
int dp_fd = open("/dev/poll", O_WRONLY);
a.fd = 0; /* stdin */
a.events = POLLIN; /* we monitor for readability, POLLIN=1 */
a.revents = 0;
write(dp_fd, &a, sizeof(a));
a.fd = 0;
a.events = 34; /* filled in with bogus number to show malfunctioning */
a.revents = 0;
printf("DP_ISPOLLED returns: %d\n", ioctl(dp_fd, DP_ISPOLLED, &a));
printf("a.fd=%d, a.events=%hd, a.revents=%hd\n", a.fd, a.events,
a.revents);
According to the documentation of /dev/poll and namely DP_ISPOLLED this
program is supposed to print the following:
DP_ISPOLLED returns: 1
a.fd=0, a.events=1, a.revents=0
However it prints the following:
DP_ISPOLLED returns: 1
a.fd=0, a.events=34, a.revents=1
You can take any number instead of '34' and it will simply remain untouched
after the DP_ISPOLLED ioctl-request.
I hope it's clear now that the solaris8 and solaris9 (and probably solaris7
with /dev/poll patch too) DP_ISPOLLED implementation is broken.
This bug is also easily illustrated by looking at the solaris8 kernel sourcecode:
<snippet osnet_volume/usr/src/uts/common/io/devpoll.c:dpioctl()>
case DP_ISPOLLED:
pollfd_t pollfd;
polldat_t *pdp;
if (pollfd.fd < 0) {
mutex_exit(&pcp->pc_lock);
break;
pdp = pcache_lookup_fd(pcp, pollfd.fd);
if ((pdp != NULL) && (pdp->pd_fd == pollfd.fd) &&
(pdp->pd_fp != NULL)) {
pollfd.revents = pdp->pd_events;
if (copyout(&pollfd, (caddr_t)arg,
sizeof(pollfd_t))) {
mutex_exit(&pcp->pc_lock);
DP_REFRELE(dpep);
return (set_errno(EFAULT));
*rvalp = 1;
</snippet>
its' clearly visible that the code writes the current monitored events to
the revents field:
'pollfd.revents = pdp->pd_events;'
and that it doesnt set revents to zero.
It's funny to see that this has been like this since Solaris8 (possibly 7). That means nobody ever used DP_ISPOLLED that way or people were simply to lazy to file a bug report.
Another funny thing related to this. is that Hewlett-Packard did seem to know about this. Since HP-UX11i version 1.6 they also support /dev/poll. From their manual page i ll quote some sentences from their WARNING session:
"The ioctl(DP_ISPOLLED) system call also returns its result in the revents member of the pollfd structure, in order to be compatible with the implementation of the /dev/poll driver by some other vendors."
Hopefully this will get fixed.
I also like to reexpress my very negative feelings towards the fact that you're not able to file bug reports when you do not have a support contract. Ridiculous.
Thanks,
bighawk

Have I mentioned how much i love my playbook now Great job on os 2.0

[bdb bug]repeatly open and close db may cause memory leak

my test code is very simple :
char *filename = "xxx.db";
char *dbname = "xxx";
for( ; ;)
DB *dbp;
DB_TXN *txnp;
db_create(&dbp,dbenvp, 0);
dbenvp->txn_begin(dbenvp, NULL, &txnp, 0);
ret = dbp->open(dbp, txnp, filename, dbname, DB_BTREE, DB_CREATE, 0);
if(ret != 0)
printf("failed to open db:%s\n",db_strerror(ret));
return 0;
txnp->commit(txnp, 0);
dbp->close(dbp, DB_NOSYNC);
I try to run my test program for a long time opening and closing db repeatly, then use the PS command and find the RSS is increasing slowly:
ps -va
PID TTY STAT TIME MAJFL TRS DRS RSS %MEM COMMAND
1986 pts/0 S 0:00 466 588 4999 980 0.3 -bash
2615 pts/0 R 0:01 588 2 5141 2500 0.9 ./test
after a few minutes：
ps -va
PID TTY STAT TIME MAJFL TRS DRS RSS %MEM COMMAND
1986 pts/0 S 0:00 473 588 4999 976 0.3 -bash
2615 pts/0 R 30:02 689 2 156561 117892 46.2 ./test
I had read bdb's source code before, so i tried to debug it for about a week and found something like a bug:
If open a db with both filename and dbname, bdb will open a db handle for master db and a db handle for subdb,
both of the two handle will get an fileid by a internal api called __dbreg_get_id, however, just the subdb's id will be
return to bdb's log region by calling __dbreg_pop_id. It leads to a id leak if I tried to open and close the db
repeatly, as a result， __dbreg_add_dbentry will call realloc repeatly to enlarge the dbentry area, this seens to be
the reason for RSS increasing.
Is it not a BUG?
sorry for my pool english :)
Edited by: user9222236 on 2010-2-25 下午10:38

I have tested my program using Oracle Berkeley DB release 4.8.26 and 4.7.25 in redhat 9.0 (Kernel 2.4.20-8smp on an i686) and AIX Version 5.
The problem is easy to be reproduced by calling the open method of db handle with both filename and dbname being specified and calling the close method.
My program is very simple:
#include <stdlib.h>
#include <stdio.h>
#include <sys/time.h>
#include "db.h"
int main(int argc, char * argv[])
int ret, count;
DB_ENV *dbenvp;
char * filename = "test.dbf";
char * dbname = "test";
db_env_create(&dbenvp, 0);
dbenvp->open(dbenvp, "/home/bdb/code/test/env",DB_CREATE|DB_INIT_LOCK|DB_INIT_LOG|DB_INIT_TXN|DB_INIT_MPOOL, 0);
for(count = 0 ; count < 10000000 ; count++)
DB *dbp;
DB_TXN *txnp;
db_create(&dbp,dbenvp, 0);
dbenvp->txn_begin(dbenvp, NULL, &txnp, 0);
ret = dbp->open(dbp, txnp, filename, dbname, DB_BTREE, DB_CREATE, 0);
if(ret != 0)
printf("failed to open db:%s\n",db_strerror(ret));
return 0;
txnp->commit(txnp, 0);
dbp->close(dbp, DB_NOSYNC);
dbenvp->close(dbenvp, 0);
return 0;
DB_CONFIG is like below:
set_cachesize 0 20000 0
set_flags db_auto_commit
set_flags db_txn_nosync
set_flags db_log_inmemory
set_lk_detect db_lock_minlocks
Edited by: user9222236 on 2010-2-28 下午5:42
Edited by: user9222236 on 2010-2-28 下午5:45

Multiple return values (Bug-ID 4222792)

I had exactly the same request for the same 3 reasons: strong type safety and code correctness verification at compile-time, code readability and ease of mantenance, performance.
Here is what Sun replied to me:
Autoboxing and varargs are provided as part of
JSRs 14 and 201
http://jcp.org/en/jsr/detail?id=14
http://jcp.org/en/jsr/detail?id=201
See also:
http://forum.java.sun.com/forum.jsp?forum=316
http://developer.java.sun.com/developer/earlyAccess/adding_generics/index.html
Multiple return values is covered by Bug-ID 4222792
Typically this is done by returning an array.
http://developer.java.sun.com/developer/bugParade/bugs/4222792.html
That's exactly the problem: we dynamically create instances of array objects that would better fit well within the operand stack without stressing the garbage collector with temporary Array object instances (and with their backing store: 2 separate allocations that need to be recycled when it is clearly a pollution that the operand stack would clean up more efficiently)
If you would like to engage in a discussion with the Java Language developers, the Generics forum would be a better place:
http://forum.java.sun.com/forum.jsp?forum=316
I know that (my report was already refering to the JSR for language extension) Generics is not what I was refering to (even if a generic could handle multiple return values, it would still be an allocated Object
instance to pack them, i.e. just less convenient than using a static class for type safety.
The most common case of multiple return values involve values that have known static datatypes and that should be checked with strong typesafety.
The simple case that involves returning two ints then will require at least two object instances and will not solve the garbage collection overhead.
Using a array of variable objects is exactly similar, except that it requires two instances for the components and one instance for the generic array container. Using extra method parameters with Integer, Byte, ... boxing objects is more efficient, but for now the only practical solution (which causes the least pollution in the VM allocator and garbage collector) is to use a custom class to store the return values in a single instance.
This is not natural, and needlessly complexifies many interfaces.
So to avoid this pollution, some solutions are used such as packing two ints into a long and returning a long, depacking the long after return (not quite clean but still much faster at run-time for methods that need to be used with high frequencies within the application. In some case, the only way to cut down the overhead is to inline methods within the caller code, and this does not help code maintenance by splitting the implementation into small methods (something that C++ can do very easily, both because it supports native types parameters by reference, and because it also supports inline methods).
Finally, suppose we don't want to use tricky code, difficult to maintain, then we'll have to use boxing Object types to allow passing arguments by reference. Shamely boxed native types cannot be allocated on the operand stack as local variables, so we need to instanciate these local variables before call, and we loose the capacity to track the cases where these local variables are not really initialized by an effective call to the method that will assign them. This does not help debugging, and is against the concept of a strongly typed language like Java should be:
Java makes lots of efforts to track uninitialized variables, but has no way to determine if an already instanciated Object instance refered in a local variable has effectively received an effective assignment because only the instanciation is kept. A typical code will then need to be written like this:
Integer a = null;
Integer b = null;
if (some condition) {
//call.method(a, b, 0, 1, "dummy input arg");
// the method is supposed to have assigned a value to a and b,
// but can't if a and b have not been instanciated, so we perform:
call.method(a = new Integer(), b = new Integer(), 0, 1, "dummy input
arg");
// we must suppose that the method has modified (not initialized!)
the value
// of a and b instances.
now.use(a.value(), b.value())
// are we sure here that a and b have received a value????
// the code may be detected at run-time (a null exception)
// or completely undetected (the method() above was called but it
// forgot to assign a value to its referenced objects a and b, in which
// case we are calling in fact: now.use(0, 0); with the default values
// or a and b, assigned when they were instanciated)
Very tricky... Hard to debug. It would be much simpler if we just used:
int a;
int b;
if (some condition) {
(a, b) = call.method(0, 1, "dummy input arg");
now.use(a, b);
The compiler would immediately detect the case where a and b are in fact not always initialized (possible use bere initialization), and the first invoked call.method() would not have to check if its arguments are not null, it would not compile if it forgets to return two values in some code path...
There's no need to provide extra boxing objects in the source as well as at run-time, and there's no stress added to the VM allocator or garbage collector simply because return values are only allocated on the perand stack by the caller, directly instanciated within the callee which MUST (checked at compile-time) create such instances by using the return statement to instanciate them, and the caller now just needs to use directly the variables which were referenced before call (here a and b). Clean and mean. And it allows strong typechecking as well (so this is a real help for programmers.
Note that the signature of the method() above is:
class call {
(int, int) method(int, int, String) { ... }
id est:
class "call", member name "method", member type "(IILjava.lang.string;)II"
This last signature means that the method can only be called by returning the value into a pair of variables of type int, or using the return value as a pair of actual arguments for another method call such as:
call.method(call.method("dummy input arg"), "other dummy input arg")
This is strongly typed and convenient to write and debug and very efficient at run-time...

Can anyone give me some real-world examples where
multiple return values aren't better captured in a
class that logically groups those values? I can of
course give hundreds of examples for why it's better
to capture method arguments as multiple values instead
of as one "logical object", but whenever I've hankered
for multiple return values, I end up rethinking my
strategy and rewriting my code to be better Object
Oriented.I'd personally say you're usually right. There's almost always a O-O way of avoiding the situation.
Sometimes though, you really do just want to return "two ints" from a function. There's no logical object you can think of to put them in. So you end up polluting the namespace:
public class MyUsefulClass {
public TwoInts calculateSomething(int a, int b, int c) {
public static class TwoInts {
    //now, do I use two public int fields here, making it
    //in essence a struct?
   //or do I make my two ints private & final, which
   //requires a constructor & two getters?
//and while I'm at it, is it worth implementing
//equals(), how about hashCode()? clone()?
//readResolve() ?
}The answer to most of the questions for something as simple as "TwoInts" is usually "no: its not worth implementing those methods", but I still have to think about them.
More to the point, the TwoInts class looks so ugly polluting the top level namespace like that, MyUsefulClass.TwoInts is public, that I don't think I've ever actually created that class. I always find some way to avoid it, even if the workaround is just as ugly.
For myself, I'd like to see some simple pass-by-value "Tuple" type. My fear is it'd be abused as a way for lazy programmers to avoid creating objects when they should have a logical type for readability & maintainability.
Anyone who has maintained code where someone has passed in all their arguments as (mutable!) Maps, Collections and/or Arrays and "returned" values by mutating those structures knows what a nightmare it can be. Which I suppose is an argument that cuts both ways: on the one hand you can say: "why add Tuples which would be another easy thing to abuse", on the other: "why not add Tuples, given Arrays and the Collections framework already allow bad programmers to produce unmainable mush. One more feature isn't going to make a difference either way".
Ho hum.

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https://addons.mozilla.org/en-US/firefox/addon/noscript/
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