I have a program witch is a xmpp client that connect to a server.
I use gloox library to do that.
When I run the program, it runs ok and connects to the server.
But when I run it under valgrind, the program never sends
<iq id='uid:4efa1893:327b23c6' type='set' from='user#server/ressource' xmlns='jabber:client'><session xmlns='urn:ietf:params:xml:ns:xmpp-session'/></iq>
to the server.
Had anybody experience such problem?
Are there any parameter I specially need to run valgrind with to make sure that it is the same environement as a normal program execution?
The very first question is: did Valgrind report any errors in the execution of your program?
If your program is well-defined, and Valgrind didn't report any errors in it, then the program is supposed to behave exactly the same way under Valgrind as without it (only slower); no special settings required.
It is somewhat more likely that Valgrind did report some errors, and if so, your program is likely not well-defined, in which case your question is mute -- your program doesn't work the same because it is not well-defined (i.e. depends on undefined behavior).
Related
I need to write a program that will halt the existing running program in the system and prompt for a question. After answering the question the running program will continue. [This halt will occur after a fixed interval of time.]
I need to implement the pause/resume feature.
Is it feasible?
If yes then what would be the approach?
Note: Please ask for any clarification, If I am unable express my problem statement.
When I run a code in OMNeT++ (eclipse based IDE), the simulation crashes after certain number of events. So to check for a memory leak, I used VALGRIND. When I run the code using this valgrind profiler, my simulation runs perfectly fine. I don't know the reason for this peculiar behavior. Can someone explain the reason behind this ?
Probably a 'heisenbug". I.e. an issue that changes its behavior if you try to examine it. It could be an uninitialized variable or other obscure bug that did not surface if the program starts with a different memory layout (i.e. under valgrind).
I would still look into the valgring logs, even if the crash does not occur as the logs may cotain some hints.
Is there possibility to show what's going on under specified process in Linux?
For example, i run SQL query -> select evil_function();
and notice that process under Linux uses all cpu.
So is there something with what I can see whats going on under this process?
What I want is to see what queries is running under this process.
Thanks!
strace will tell you what system calls the process is making.
To see what called routines are taking the most CPU, you need to run a profiling tool, and make sure the executable of the process you in compiled correctly (sometimes it needs to be instrumented during compilation for profiling, sometimes it just needs to be compiled with debug symbols, or not stripped of them after compilation).
You might want to look at oprofile, valgrind, gprof and for starters on free tools - there are also commercial products available.
Here are a few links:
http://www.pixelbeat.org/programming/profiling/
http://en.wikipedia.org/wiki/List_of_performance_analysis_tools
You are mixing a whole bunch of things.
If you are talking about MySQL do:
show processlist;
For info specifically about linux processes, you can strace the process to get a list of system function that it calls. Unless you are experienced with linux this will be useless to you.
If the process is paused then you can find out what function it is stopped on, but that's probably not what you want, since you say the process is running.
There are also various tools that can give you info on what parts of the disk the process is reading, and how much memory it's allocating.
And finally you can use gdb to break into the process and single step your way through it to see exactly what it's doing. This will also likely be useless to you since an SQL server does a LOT of things - far to many to understand by this method.
From what experience I have programming whenever a program has a problem it crashes, whether it is from an unhanded exception or a piece of code that should have been checked for errors, but was not and threw one. What would cause a program to completely freeze a system to the point of requiring a restart.
Edit: Thanks for the answers. As for the language and OS this question was inspired by me playing Fallout and the game freezing twice in an hour causing me to have to restart the xbox, so I am guessing c++.
A million different things. The most common that come to mind are:
Spawning too many threads or processes, which drowns the OS scheduler.
Gobbling too much RAM, which puts the memory manager into page-fault hell.
In a Dotnet/Java type environment its quite difficult to seize a system up, because the Runtime keeps you code at a distance from the OS.
Closer to the metal say C or C++, Assembly etc you have to play fair with the rest of the system - If you dont have it already grab a copy of Petzold and observe/experiment yourself with the amount of 'boilerplate' code to get a single Window running...
Even closer, down at the driver level all sorts of things can happen...
There are number of reasons, being internal or external that leads to deadlocked application, more general case is when something is being asked for by a program but is not given that leads to infinite waiting, the practical example to this is, a program writes some text to a file, but when it is about to open a file for writing, same file is opened by any other application, so the requesting app will wait (freeze in some cases if not coded properly) until it gets exclusive control of the file.
And a critical freeze that leads to restarting the system is when the file which is asked for is something which very important for the OS. However, you may not need to restart the system in order to get it back to normal, unless the program which was frozen is written in a language that produces native binary, i.e. C/C++ to be precise. So if application is written in a language which works with the concept of managed code, like any .NET language, it will not need a system restart to get things back to normal.
page faults, trying to access inaccessible data or memory(acces violation), incompatible data types etc.
Whether this is possible I don't know, but it would mighty useful!
I have a process that fails periodically (running in Windows 2000). I then have just one chance to react to it before having to restart it and painfully wait for it to fail again. I didn't write the process so don't have the source to debug. The failure is seemingly random.
With a snapshot of the process I could repeatedly and quickly test reactions to the failure.
I had thought of running inside a VM but this isn't possible in this instance.
EDIT:
#Jon Cage asked:
When you say a snapshot, you mean capturing a process when it's about to fail (including memory, program state etc. etc.) ...and then replaying it's final few seconds repeatedly to see what effect it has on some other component?
This is exactly what I mean!
I think minidump is what you are looking for.
You can also used Userdump:
The User Mode Process Dumper
(userdump) dumps any running Win32
processes memory image (including
system processes such as csrss.exe,
winlogon.exe, services.exe, etc) on
the fly, without attaching a debugger,
or terminating target processes.
Generated dump file can be analyzed or
debugged by using the standard
debugging tools.
This article shows you how to use it.
My best bet is to start the process in a debugger (OllyDbg being my preferred tool).
The process will pause on an exception, and you can try to figure out what happened shortly before that.
This needs some understanding of assembler and does not allow to create a snapshot of the process for later analysis. You would need to write your own debugger for that - it should be theoretically possible.