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• CFHost DNS Resolution - When is it OK to use synchronous API?

  - by Jasarien

  I went to the iPhone Developer Tech Talk a few months ago and asked one of the gurus there about the lack of NSHost on the iPhone. Some code I was porting to the iPhone made significant use of NSHost throughout its networking code. I was told that NSHost is on the iPhone, but its private. I was also told that NSHost is a synchronous API and that I shouldn't use it anyway. (If anyone could elaborate on why it shouldn't be used, as a bonus, that'd be great.) I can see the caveats of using synchronous API's on the main thread in that they'll block until complete - and that's never a good thing with network code because there are so many factors that could cause the API to block the thread for a significant amount of time. My solution was to write a wrapper around CFHost's asynchronous resolution functions. The result works quite well, and I'm considering releasing it into the public domain. But my question is this: Say my app only resolves a hostname once per run, during the connecting phase, and then cache's it for the rest of the session. During the time it is resolving, a modal screen is shown telling the user "Connecting" with a nice spinner. Does it really matter whether or not the resolution is asynchronous?? The user has to wait to connect anyway, and the resolution is only done on the first connection. Subsequent connections use the cached result of the resolution. When is it OK to be synchronous and when should things be asynchronous?

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• Reference-type conversion operators: asking for trouble?

  - by Ben

  When I compile the following code using g++ class A {}; void foo(A&) {} int main() { foo(A()); return 0; } I get the following error messages: > g++ test.cpp -o test test.cpp: In function ‘int main()’: test.cpp:10: error: invalid initialization of non-const reference of type ‘A&’ from a temporary of type ‘A’ test.cpp:6: error: in passing argument 1 of ‘void foo(A&)’ After some reflection, these errors make plenty of sense to me. A() is just a temporary value, not an assignable location on the stack, so it wouldn't seem to have an address. If it doesn't have an address, then I can't hold a reference to it. Okay, fine. But wait! If I add the following conversion operator to the class A class A { public: operator A&() { return *this; } }; then all is well! My question is whether this even remotely safe. What exactly does this point to when A() is constructed as a temporary value? I am given some confidence by the fact that void foo(const A&) {} can accept temporary values according to g++ and all other compilers I've used. The const keyword can always be cast away, so it would surprise me if there were any actual semantic differences between a const A& parameter and an A& parameter. So I guess that's another way of asking my question: why is a const reference to a temporary value considered safe by the compiler whereas a non-const reference is not?

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• Use $_FILES on a page called by .ajax

  - by RachelD

  I have two .php pages that I'm working with. Index.php has a file upload form that posts back to index.php. I can access the $_FILES no problem on index.php after submitting the form. My issue is that I want (after the form submit and the page loads) to use .ajax (jQuery) to call another .php file so that file can open and process some of the rows and return the results to ajax. The ajax then displays the results and recursively calls itself to process the next batch of rows. Basically I want to process (put in the DB etc) the csv in chunks and display it for the user in between chunks. Im doing it this way because the files are 400,000+ rows and the user doesnt want to wait the 10+ min for them all to be processed. I dont want to move this file (save it) because I just need to process it and throw it away and if a user closes the page while its processing the file wont be thrown away. I could cron script it but I dont want to. What I would really like to do is pass the (single) $_FILES through .ajax OR Save it in a $_POST or $_SESSION to use on the second page. Is there any hope for my cause? Heres the ajax code if that helps: function processCSV(startIndex, length) { $.ajax({ url: "ajax-targets/process-csv.php", dataType: "json", type: "POST", data: { startIndex: startIndex, length: length }, timeout: 60000, // 1000 = 1 sec success: function(data) { // JQuery to display the rows from the CSV var newStart = startIndex+length; if(newStart <= data['csvNumRows']) { processCSV(newStart, length); } } }); } processCSV(1, 2); }); P.S. I did try this Passing $_FILES or $_POST to a new page with PHP but its not working for me :( SOS.

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• Why isn't UIScrollView always calling viewDidLoad on subviews?

  - by Rob S.

  I'm a bit confused on the behaviour of UIScrollView as it pertains to subview loading. In my app, I lazily load subviews into my scroller. Most of the time, -viewDidLoad is called on the subview immediately after adding it the UIScrollView. There is one scenario where it isn't being called. At the 'end' of my scroll view I have a "please wait" view. When it is fully scrolled on to the page, it fades out, I add the subview and -viewDidLoad is not called. In this case, when I remove the last subview and add another subview, I get nothing. I've tried [scrollView setNeedsDisplay] and [scrollView setNeedsLayout] to no avail. I've also sent the same messages to the view I just added - no dice. Does anyone have any insight here? Many people have many questions about -viewDidLoad and I haven't been able to find one related to direct subviews inside of a scrollview. Or I have and I haven't realized it :) Thanks in advance! Rob

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• The Coolest Parts of Windows API

  - by Andreas Rejbrand

  I have noticed that there are quite a few community wikis about "Tips & Tricks" or "Hidden Features" in programming languages and APIs here at Stack Overflow. But I could not find any about my own personal favourites: Win32 API and Delphi. Therefore I start my "own" CW about Win32 API. There are (at least) two kinds of Win API users: those that have been brought up using Windows API in C/C++, and those that have been brought up using some level of abstraction above the Windows API. I belong to the latter category, being brought up using Delphi's VCL. But over the last five years, I have become increasingly interested in the underlaying API of the Windows operating system, and today I work a lot with it. Depending on which category a programmer belongs to, he (or possibly she) will think that different things are "cool" in the Windows API. For instance, whereas a VCL-brought up developer might think it it very cool to var errIcon: HICON; begin errIcon := LoadIcon(0, IDI_ERROR); DrawIcon(Canvas.Handle, 10, 10, errIcon), a programmer brought up using Windows API in C will not be as impressed. But no matter how you are "brought up": what are the coolest "tricks" in Windows API? I start by listing a few of my own favourites, some of which are more "cool" than "useful", though: LoadIcon and MessageBeep can load/play system default icons and sounds. Open the CD tray: mciSendString('Set cdaudio door open wait', nil, 0, 0); Fade out the screen (Windows Vista and later) and turn of the monitor: SendMessage(Application.Handle, WM_SYSCOMMAND, SC_MONITORPOWER, 2); GetWindowDC(GetDesktopWindow) returns the DC of the desktop.

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• Help with Cygwin bash file

  - by Mestika

  Hi, I have a bash file, which I’m trying to run in Cygwin on a Windows 7 platform, but I gives me some odd errors when doing so. The bash file works on my Linux system. The bach file looks like this: for ((r=0; r <10; r++)) netcat localhost 4444 < myfile.file & done wait but I’m getting an error for my for-loop. More precise it writes: ./tuning_test.bsh: line 1: syntax error near unexpected token `(' '/tuning_test.bsh: line 1: `?for ((r=0; r <10; r++)) I do not understand it because I was sure that I’ve a working bash file on my Linux. I even tried to find a for-loop example from a Linux-bash site and run it but with same error. I’m brand new to Cygwin and doesn’t know if it has some small quirks or some other thing I have to be aware of and I’ve tried to look through the documentation and FAQ on their homepage. Sincere Mestika

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• Winforms: How to display a "loading" form?

  - by Martijn

  I have a grid and when a row is double clicked a form is loaded. However a lot of data must be loaded, so I'd like to display a simple form with the text 'loading, please wait..'. And when all loading is finished, the form must disappear. This is what I have right now, but it doesn't work: Code that invokes the form with lots of data: FormWithLotData form = new FormWithLotData(); form.ShowDialog(this); Constructor of FormWithLotData: // Show load form FormIsLoading frm = new FormIsLoading(); _CloseLoadForm closeForm = new _CloseLoadForm(frm.Close); System.Threading.Thread thread = new System.Threading.Thread(frm.Show); thread.Start(); InitializeComponent(); this.Visible = false; LoadAllData(); this.Visible = true; // Close load form Invoke(closeForm); Hope you can help me out. EDIT: I'd like to show an animated gif on the loading form.

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• Problem using UnhandledException in Windows Mobile app

  - by MusiGenesis

  I have a Windows Mobile program that accesses an attached device through a third-party DLL. Each call to the device can take an unknown length of time, so each call includes a timeout property. If the call takes longer than the specified timeout to return, the DLL instead throws an exception which my app catches with no problem. The problem that I have is with closing the application. If my application has made a call to the DLL and is waiting for the timeout to occur, and I then close the application before the timeout occurs, my application locks up and requires the PDA to be rebooted. I can ensure that the application waits for the timeout before closing, under normal conditions. However, I am trying to use AppDomain.CurrentDomain.UnhandledException to catch any unhandled exceptions in the program and use the event to wait for this pending timeout to occur so the program can be closed finally. My problem is that this event doesn't seem to stick around long enough. If I put a MessageBox.Show("unhandled exception"); line in the event, and then throw a new unhandled exception from my application's main form, I see the message box for a split second but then it disappears without my having clicked the OK button. The documentation I've found on this event suggests that by the time it's called the application is fully committed to closing and the closing can't be stopped, but I didn't think it meant that the event method itself won't finish. What gives (I guess that's the question)? Update: In full windows (Vista) this works as expected, but only if I use the Application.ThreadException event, which doesn't exist in .Net CF 2.0.

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• Keybd is not working right =(

  - by user302131

  i can't get this to work right this should press left for 1sec then wait 10secs then right 1sec. keybd_event(0x25, 0xCB, 0, 0); // press left cout << "Ldown\n"; // so i know it worked Sleep(1000); // hold it for 1sec keybd_event(0x25, 0xCB, KEYEVENTF_KEYUP, 0);// let go of the key cout << "Lup\n"; // so i know i let go Sleep(10000); // Sleep for 10secs keybd_event(0x27, 0xCD, 0, 0); // press right cout << "Rdown\n"; // so i know i pressed right Sleep(1000); // sleep 1sec keybd_event(0x27, 0xCD, KEYEVENTF_KEYUP, 0);// let go of the key cout << "Rdown\n"; // so i know i let go. this is in a loop but it wont do anything :( unless i close the program before the key is let go then it will just keep the keydown until i press the key again. i know you can use only one key code if you want but i need to use both. so what i'm i missing?

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• Why is my multithreaded Java program not maxing out all my cores on my machine?

  - by James B

  Hi, I have a program that starts up and creates an in-memory data model and then creates a (command-line-specified) number of threads to run several string checking algorithms against an input set and that data model. The work is divided amongst the threads along the input set of strings, and then each thread iterates the same in-memory data model instance (which is never updated again, so there are no synchronization issues). I'm running this on a Windows 2003 64-bit server with 2 quadcore processors, and from looking at Windows task Manager they aren't being maxed-out, (nor are they looking like they are being particularly taxed) when I run with 10 threads. Is this normal behaviour? It appears that 7 threads all complete a similar amount of work in a similar amount of time, so would you recommend running with 7 threads instead? Should I run it with more threads?...Although I assume this could be detrimental as the JVM will do more context switching between the threads. Alternatively, should I run it with fewer threads? Alternatively, what would be the best tool I could use to measure this?...Would a profiling tool help me out here - indeed, is one of the several profilers better at detecting bottlenecks (assuming I have one here) than the rest? Note, the server is also running SQL Server 2005 (this may or may not be relevant), but nothing much is happening on that database when I am running my program. Note also, the threads are only doing string matching, they aren't doing any I/O or database work or anything else they may need to wait on. Thanks in advance, -James

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• question about InnoDB deadlock in MySQL?

  - by WilliamLou

  I found this kind of interesting problem in MySQL InnoDB engine, could anyone explain why the engine always claim it's a deadlock. First, I created a table with a single row, single column: CREATE TABLE `SeqNum` (`current_seq_num` bigint(30) NOT NULL default '0', PRIMARY KEY (`current_seq_num`) ) ENGINE=InnoDB DEFAULT CHARSET=utf8 | Now, I have two MySQL connector threads, In thread1: mysql> begin; Query OK, 0 rows affected (0.00 sec) mysql> select `current_seq_num` into @curr_seq FROM SeqNum FOR UPDATE; Query OK, 1 row affected (0.00 sec) Now, in thread2, I did the exactly same: mysql> begin; Query OK, 0 rows affected (0.00 sec) mysql> select `current_seq_num` into @curr_seq FROM SeqNum FOR UPDATE; before the default innodb_lock_wait_timeout, the thread2 just wait for thread1 to release its exclusive lock on the table, and it's normal. However, in thread1, if I input the following update query: mysql> update SeqNum set `current_seq_num` = 8; ERROR 1213 (40001): Deadlock found when trying to get lock; try restarting transaction Now, thread2 get the select query finished because thread1 quits. In addition, in thread1, if I input the update query with a where clause, it can be executed very well: mysql> update SeqNum set `current_seq_num` = 8 where `current_seq_num` =5 Query OK, 1 row affected (0.00 sec) Could anyone explain this?

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• Java Error beeping

  - by user1281385

  Im working on a Chat client that i didnt write the bulk of the code for. It works fine however when someone sends a message it beeps (system error beep) when using Java 7. Java 6 and below doesn't have this beep. I cant seem to find whats causing the beep is there any way to find it ? I dont think its calling beep as i have public class nobeep extends sun.awt.windows.WToolkit { @Override public void beep() { System.out.println("tried to beep"); new Exception().printStackTrace(); } } and then called System.setProperty("awt.toolkit", "nobeep"); in the main method. Using the method to send a beep doesnt make it beep. Its only when sent normally. Is there a quick way to track down the cause of the beep ? Edit: After looking in the bugs database - its confirmed. http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=7194469 I know it says no work around but is there one (java not c++) or just wait until update 8 ?

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• PHP sessions causing Apache to hang indefinitely

  - by Kmaid

  The problem is that every so often a page that writes to a Session will cause apache to hang forever for a particular session. Once this error occurs for one user any further modifications to any session of any user will cause the website to hang for this user. This problem has been my sole focus for days. I have a development VPS running Windows 2003 and default latest version of XAMPP using the standard PHP session handler. The code in question actually runs on two other machines perfectly normally so although my common sense says it’s a web server configuration issue but at this point I am willing to try anything. On further investigation there are no errors in the Apache, PHP or System event log. Resources are abundant and there is no “AJAX shit storm” or more than a couple writes to a session per page. I have also implemented session_write_close() wherever possible to try and help elevate the problem. I have checked the session’s directory which is set to “C:\windows\Temp” and found that once a user enters this hanging phase that the corresponding session file is exclusively locked and the only way to resolve this is to stop Apache and wait a few moments for the files to become unlocked and delete them. I am not wondering if deletion is required. The Sessions themselves only contain 4 bits of information. ShoppingCartID, UserID, UserLevel and Refering URL and are alphanumerical with an occasional slash. My PHP.INI’s session section is configured like this: session.save_handler = files session.save_path = "C:\WINDOWS\Temp" session.use_cookies = 1 session.name = PHPSESSID session.auto_start = 0 session.cookie_lifetime = 0 session.cookie_path = / session.cookie_domain = session.cookie_httponly = session.serialize_handler = php session.gc_probability = 1 session.gc_divisor = 100 session.gc_maxlifetime = 1440 session.bug_compat_42 = 1 session.bug_compat_warn = 1 session.referer_check = session.entropy_length = 0 session.entropy_file = session.cache_limiter = nocache session.cache_expire = 180 session.use_trans_sid = 0 session.hash_function = 0 session.hash_bits_per_character = 4 I have tried everything I can think of and the whole problem is now a blur to me. Any ideas would be appreciated and thanks for your time reading this :)

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• Any suggestions for good automated web load testing tool?

  - by fmunkert

  What are some good automated tools for load testing (stress testing) web applications, that do not use record and replay of HTTP network packets? I am aware that there are numerous load testing tools on the market that record and replay HTTP network packets. But these are unsuitable for my purpose, because of this: The HTTP packet format changes very often in our application (e.g. when we optimize an AJAX call). We do not want to adapt all test scripts just because there is a slight change in HTTP packet format. Our test team shall not need to know any internals about our application to write their test scripts. A tool that replays HTTP packets, however, requires the team to know the format of HTTP requests and responses, such that they can adapt details of the replayed HTTP packets (e.g. user name). The automated load testing tool I am looking for should be able to let the test team write "black box" test scripts such as: Invoke web page at URL http://... . First, enter XXX into text field XXX. Then, press button XXX. Wait until response has been received from web server. Verify that text field XXX now contains the text XXX. The tool should be able to simulate up to several 1000 users, and it should be compatible with web applications using ASP.NET and AJAX.

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• python scritp problem once build and package it

  - by Apache

  hi expert, i've written python script to scan wifi and send data to the server, i set interval value, so it keep on scanning and send the data, it read from config.txt file where i set the interval value to scan, i also add yes/no in my config file, so is 'no' it will scan only once and if 'yes' it will scan according to the interval level, my code as below import time,..... from threading import Event, Thread class RepeatTimer(Thread): def __init__(self, interval, function, iterations=0, args=[], kwargs={}): Thread.__init__(self) self.interval = interval self.function = function self.iterations = iterations self.args = args self.kwargs = kwargs self.finished = Event() def run(self): count = 0 while not self.finished.is_set() and (self.iterations <= 0 or count < self.iterations): self.finished.wait(self.interval) if not self.finished.is_set(): self.function(*self.args, **self.kwargs) count += 1 def cancel(self): self.finished.set() def scanWifi(self): #scanning process and sending data done here obj = JW() if status == "yes": t = RepeatTimer(int(intervalTime),obj.scanWifi) t.start() else: obj.scanWifi() once i package my code, its only run when i set my config file set to 'no' where it scan only once, but when i set my config file to 'yes', there is no progress at all, so i found that there is problem with my class RepeatTimer(Timer) once build, but don't know how to solve can anyone help me thanks

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• cx_Oracle makes subprocess give OSError

  - by Shrikant Sharat

  I am trying to use the cx_Oracle module with python 2.6.6 on ubuntu Maverick, with Oracle 11gR2 Enterprise edition. I am able to connect to my oracle db just fine, but once I do that, the subprocess module does not work anymore. Here is an iPython session that reproduces the problem... In [1]: import subprocess as sp, cx_Oracle as dbh In [2]: sp.call(['whoami']) sharat Out[2]: 0 In [3]: con = dbh.connect('system', 'password') In [4]: con.close() In [5]: sp.call(['whomai']) --------------------------------------------------------------------------- OSError Traceback (most recent call last) /home/sharat/desk/calypso-launcher/<ipython console> in <module>() /usr/lib/python2.6/subprocess.pyc in call(*popenargs, **kwargs) 468 retcode = call(["ls", "-l"]) 469 """ --> 470 return Popen(*popenargs, **kwargs).wait() 471 472 /usr/lib/python2.6/subprocess.pyc in __init__(self, args, bufsize, executable, stdin, stdout, stderr, preexec_fn, close_fds, shell, cwd, env, universal_newlines, startupinfo, creationflags) 621 p2cread, p2cwrite, 622 c2pread, c2pwrite, --> 623 errread, errwrite) 624 625 if mswindows: /usr/lib/python2.6/subprocess.pyc in _execute_child(self, args, executable, preexec_fn, close_fds, cwd, env, universal_newlines, startupinfo, creationflags, shell, p2cread, p2cwrite, c2pread, c2pwrite, errread, errwrite) 1134 1135 if data != "": -> 1136 _eintr_retry_call(os.waitpid, self.pid, 0) 1137 child_exception = pickle.loads(data) 1138 for fd in (p2cwrite, c2pread, errread): /usr/lib/python2.6/subprocess.pyc in _eintr_retry_call(func, *args) 453 while True: 454 try: --> 455 return func(*args) 456 except OSError, e: 457 if e.errno == errno.EINTR: OSError: [Errno 10] No child processes So, the call to sp.call works fine before connecting to oracle, but breaks after that. Even if I have closed the connection to the database. Looking around, I found http://bugs.python.org/issue1731717 as somewhat related to this issue, but I am not dealing with threads here. I don't know if cx_Oracle is. Moreover, the above issue mentions that adding a time.sleep(1) fixes it, but it didn't help me. Any help appreciated. Thanks.

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• Signals and Variables in VHDL - Problem

  - by Morano88

  I have a signal and this signal is a bitvector. The length of the bitvector depends on an input n, it is not fixed. In order to find the length, I have to do some computations. Can I define a signal after defining the variables ? It is ggiving me errors when I do that. It is working fine If I keep the signal before the variables .. but I don't want that .. the length of Z depends on the computations of the variables. What is the solution ? library IEEE; use IEEE.STD_LOGIC_1164.ALL; use IEEE.STD_LOGIC_ARITH.ALL; use IEEE.STD_LOGIC_UNSIGNED.ALL; entity BSD_Full_Comp is Generic (n:integer:=8); Port(X, Y : inout std_logic_vector(n-1 downto 0); FZ : out std_logic_vector(1 downto 0)); end BSD_Full_Comp; architecture struct of BSD_Full_Comp is Component BSD_BitComparator Port ( Ai_1 : inout STD_LOGIC; Ai_0 : inout STD_LOGIC; Bi_1 : inout STD_LOGIC; Bi_0 : inout STD_LOGIC; S1 : out STD_LOGIC; S0 : out STD_LOGIC ); END Component; Signal Z : std_logic_vector(2*n-3 downto 0); begin ass : process Variable length : integer := n; Variable pow : integer :=0 ; Variable ZS : integer :=0; begin while length /= 0 loop length := length/2; pow := pow+1; end loop; length := 2 ** pow; ZS := length - n; wait; end process; end struct;

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• c# CF Restart a thread

  - by Ed

  Hi all, Supose you have a form with a button that starts/stops a thread (NOT pausing or interrupting, I really need to stop the thread !) Check out this code: Constructor() { m_TestThread = new Thread(new ThreadStart(ButtonsThread)); m_bStopThread = false; } ButtonClick { // If the thread is not running, start it m_TestThread.Start(); // If the thread is running, stop it m_bStopThread = true; m_TestThread.Join(); } ThreadFunction() { while(!m_bStopThread) { // Do work } } 2 questions (remember CF): - How can I know if the thread is running (I cannot seem to access the m_pThreadState, and I've tried the C++ GetThreadExitCode(), it give false results) ? - Most important question : if I have stopped the thread, I cannot restart it, most probably because the m_TestThread.m_fStarted is still set (and it is private so I cannot access it) ! And thus m_TestThread.Start() generates an exception (StateException). Stopping the thread with an Abort() doesn't solve it. If I put my m_TestThread = null; it works, but then I create a memory leak. The GC doesn't clean up either, even if I wait for xx seconds. Anybody has an idea ? All help highly appreciated ! Grtz E

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• Jmap can't connect to to make a dump

  - by Jasper Floor

  We have an open beta of an app which occasionally causes the heapspace to overflow. The JVM reacts by going on a permanent vacation. To analyze this I would like to peek into the memory at the point where it failed. Java does not want me to do this. The process is still in memory but it doesn't seem to be recognized as a java process. The server in question is a debian Lenny server, Java 6u14 /opt/jdk/bin# ./jmap -F -dump:format=b,file=/tmp/apidump.hprof 11175 Attaching to process ID 11175, please wait... sun.jvm.hotspot.debugger.NoSuchSymbolException: Could not find symbol "gHotSpotVMTypeEntryTypeNameOffset" in any of the known library names (libjvm.so, libjvm_g.so, gamma_g) at sun.jvm.hotspot.HotSpotTypeDataBase.lookupInProcess(HotSpotTypeDataBase.java:390) at sun.jvm.hotspot.HotSpotTypeDataBase.getLongValueFromProcess(HotSpotTypeDataBase.java:371) at sun.jvm.hotspot.HotSpotTypeDataBase.readVMTypes(HotSpotTypeDataBase.java:102) at sun.jvm.hotspot.HotSpotTypeDataBase.<init>(HotSpotTypeDataBase.java:85) at sun.jvm.hotspot.bugspot.BugSpotAgent.setupVM(BugSpotAgent.java:568) at sun.jvm.hotspot.bugspot.BugSpotAgent.go(BugSpotAgent.java:494) at sun.jvm.hotspot.bugspot.BugSpotAgent.attach(BugSpotAgent.java:332) at sun.jvm.hotspot.tools.Tool.start(Tool.java:163) at sun.jvm.hotspot.tools.HeapDumper.main(HeapDumper.java:77) at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39) at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25) at java.lang.reflect.Method.invoke(Method.java:597) at sun.tools.jmap.JMap.runTool(JMap.java:179) at sun.tools.jmap.JMap.main(JMap.java:110) Debugger attached successfully. sun.jvm.hotspot.tools.HeapDumper requires a java VM process/core!

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• How to implement Session timeout in Web Server Side?

  - by Morgan Cheng

  I beheld a web framework implementing in-memory session in this way. The session object is added to Cache with timeout. When the time is out, the session is removed from Cache automatically. To protect race condition, each request should acquire lock on given session object to proceed. Each request will "touch" the session in Cache to refresh the timeout. Everything looks fine, until this scenario is discovered. Say, one operation takes a long time, longer than timeout. Another request comes and wait on session lock which is currently hold by the long-time request. Finally, the long-time request is over, it releases the lock. But, since it already takes longer time than timeout, the session object is already removed from Cache. This is obvious because the only request holding the lock doesn't have a chance to "touch" the session object in cache. The second request gets the lock but cannot retrieve the expired Session object. Oops... To fix this issue, the second request has to re-create the Session object. But, this is just like digging a buried dead body from tomb and try to bring it back to life. It causes buggy code. I'm wondering what's the best way to implement timeout in session to handle such scenario. I know that current platform must have good session mechanism. I just want to know the under-the-hood how.

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• My First F# program

  - by sudaly

  Hi I just finish writing my first F# program. Functionality wise the code works the way I wanted, but not sure if the code is efficient. I would much appreciate if someone could review the code for me and point out the areas where the code can be improved. Thanks Sudaly open System open System.IO open System.IO.Pipes open System.Text open System.Collections.Generic open System.Runtime.Serialization [<DataContract>] type Quote = { [<field: DataMember(Name="securityIdentifier") >] RicCode:string [<field: DataMember(Name="madeOn") >] MadeOn:DateTime [<field: DataMember(Name="closePrice") >] Price:float } let m_cache = new Dictionary<string, Quote>() let ParseQuoteString (quoteString:string) = let data = Encoding.Unicode.GetBytes(quoteString) let stream = new MemoryStream() stream.Write(data, 0, data.Length); stream.Position <- 0L let ser = Json.DataContractJsonSerializer(typeof<Quote array>) let results:Quote array = ser.ReadObject(stream) :?> Quote array results let RefreshCache quoteList = m_cache.Clear() quoteList |> Array.iter(fun result->m_cache.Add(result.RicCode, result)) let EstablishConnection() = let pipeServer = new NamedPipeServerStream("testpipe", PipeDirection.InOut, 4) let mutable sr = null printfn "[F#] NamedPipeServerStream thread created, Wait for a client to connect" pipeServer.WaitForConnection() printfn "[F#] Client connected." try // Stream for the request. sr <- new StreamReader(pipeServer) with | _ as e -> printfn "[F#]ERROR: %s" e.Message sr while true do let sr = EstablishConnection() // Read request from the stream. printfn "[F#] Ready to Receive data" sr.ReadLine() |> ParseQuoteString |> RefreshCache printfn "[F#]Quot Size, %d" m_cache.Count let quot = m_cache.["MSFT.OQ"] printfn "[F#]RIC: %s" quot.RicCode printfn "[F#]MadeOn: %s" (String.Format("{0:T}",quot.MadeOn)) printfn "[F#]Price: %f" quot.Price

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• Need some help/advice on WCF Per-Call Service and NServiceBus interop.

  - by Alexey

  I have WCF Per-Call service wich provides data for clients and at the same time is integrated with NServiceBus. All statefull objects are stored in UnityContainer wich is integrated into custom service host. NServiceBus is configured in service host and uses same container as service instances. Every client has its own instance context(described by Juval Lowy in his book in chapter about Durable Services). If i need to send request over bus I just use some kind of dispatcher and wait response using Thread.Sleep().Since services are per-call this is ok afaik. But I am confused a bit about messages from bus, that service must handle and provide them to clients. For some data like stock quotes I just update some kind of statefull object and and then, when clients invoke GetQuotesData() just provide data from this object. But there are numerous service messages like new quote added and etc. At this moment I have an idea to implement something like "Postman daemon" =)) and store this type of messages in instance context. Then client will invoke "GetMail()",recieve those messages and parse them. Problem is that NServiceBus messages are "Interface based" and I cant pass them over WCF, so I need to convert them to types derieved from some abstract class. Dunno what is best way to handle this situation. Will be very gratefull for any advice on this. Thanks in advance.

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• how to implement word count bash shell

  - by codemax

  hey guys. I am trying to write my own code for the word count in bash shell. I did usual way. But i wanna use pipe's output to count the word. So for eg the 1st command is cat and i am redirecting to a file called med. Now i have to use to 'dup2' function to count the words in that file. How can i write the code for my wc? This is the code for my shell pgm : void process( char* cmd[], int arg_count ) { pid_t pid; pid = fork(); char path[81]; getcwd(path,81); strcat(path,"/"); strcat(path,cmd[0]); if(pid < 0) { cout << "Fork Failed" << endl; exit(-1); } else if( pid == 0 ) { int fd; fd =open("med", O_RDONLY); dup2(fd ,0); execvp( path, cmd ); } else { wait(NULL); } } And my wordcount is : int main(int argc, char *argv[]) { char ch; int count = 0; ifstream infile(argv[1]); while(!infile.eof()) { infile.get(ch); if(ch == ' ') { count++; } } return 0; } I dont know how to do input redirection i want my code to do this : When i just type wordcount in my shell implementation, I want it to count the words in the med file by default. Thanks in advance

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• Can't disable method parenthesis auto-complete in Eclipse

  - by cvig

  I'm trying to disable the automatic closing of brackets in Eclipse, and while I've mostly succeeded, I can't stop the editor from inserting a closing parenthesis for a method call. The result is that when I type: myBool.equals(true); it inserts a closing parenthesis as soon as I type the opening parenthesis, and what I actually get is: myBool.equals(true);) I've disabled all of the auto-complete options in the Preferences - Java - Editor - Typing menu, as well as Preferences - Java - Editor - Content Assist - Fill method arguments and show guessed arguments. I also disabled the smart insert mode option under the Edit menu. Is there another option somewhere else I need to use to stop Eclipse from doing this? This is with Eclipse 3.5.2 (Build ID M20100211-1343) in case it matters. Edited to add: I should also mention that this only happens if I wait for the "intellisense" pop-up with suggested method names to appear after I type the period. If I just continuously type the code without waiting for the suggestion box to appear, the closing parenthesis doesn't get inserted.

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• Perl: Process Communcation

  - by Shiftbit

  Can anyone explain how I can successfully get my process communicating. I find the perldoc on IPC confusing. What I have so far is: $| = 1; $SIG{CHLD} = {wait}; my $parentPid = $$; if ($pid = fork();) ) { if ($pid == 0) { pipe($parentPid, $$); open PARENT, "<$parentPid"; while (<PARENT>) { print $_; } close PARENT; exit(); } else { pipe($parentPid, $pid); open CHILD, ">$pid"; or error("\nError opening: childPid\nRef: $!\n"); open (FH, "<list") or error("\nError opening: list\nRef: $!\n"); while(<FH>) { print CHILD, $_; } close FH or error("\nError closing: list\nRef: $!\n"); close CHILD or error("\nError closing: childPid\nRef: $!\n); } else { error("\nError forking\nRef: $!\n"); } First Question is what does Perldoc pipe mean by READHANDLE, WRITEHANDLE? Second Questions is can I implement a solution without relying on CPAN or other modules?

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