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• Fix Corrupted Ruby in Mac OS X Lion

  - by luckyb56

  I screwed up my ruby buy executing the command sudo easy_install pip> /usr/bin/ruby -e "$(/usr/bin/curl -fksSL https://raw.github.com/mxcl/homebrew/master/Library/Contributions/install_homebrew.rb)" It showed error: Couldn't find index page for '-e' (maybe misspelled?) No local packages or download links found for -e error: Could not find suitable distribution for Requirement.parse('-e') After that when I tried to install Brew by: /usr/bin/ruby -e "$(/usr/bin/curl -fksSL https://raw.github.com/mxcl/homebrew/master/Library/Contributions/install_homebrew.rb)" It shows error which I have no idea: /usr/bin/ruby: line 1: Searching: command not found /usr/bin/ruby: line 2: Best: command not found /usr/bin/ruby: line 3: Processing: command not found Usage: pip COMMAND [OPTIONS] pip: error: No command by the name pip 1.1 (maybe you meant "pip install 1.1") /usr/bin/ruby: line 5: Installing: command not found /usr/bin/ruby: line 6: Installing: command not found /usr/bin/ruby: line 8: Using: command not found /usr/bin/ruby: line 9: Processing: command not found /usr/bin/ruby: line 10: Finished: command not found /usr/bin/ruby: line 11: Searching: command not found /usr/bin/ruby: line 12: Reading: command not found /usr/bin/ruby: line 13: syntax error near unexpected token `(' /usr/bin/ruby: line 13: `Scanning index of all packages (this may take a while)' Can this be fixed?

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• Why can't execute GRUB command on Debian Squeeze 2.6 with GRUB already installed?

  - by Mikalaj

  I installed Debian Squeeze 2.6 (on a recently bought server) with a software RAID1. During installation I installed GRUB loader (1.9 version). System boots OK with GRAB loader BUT right after authorization it cannot execute GRUB command (I want to copy the GRUB from the SDA to SDB). System warning right after GRUB command invocation looks as: root@servername:~# grub -bash: grub: command not found How it could be? (GRUB already installed and no any other OS was installed at all)

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• Unix command to suspend a job while there is console activity?

  - by Joseph Turian

  I want to do a large disk transfer, which slows down responsiveness of my system. What I want is a Unix command that will only run the command after I have been idle at the console for a few minutes. And if I come back half way in, it will suspend the job. Until I walk away from my computer. Is there such a command, or software package?

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• How to start "explorer" process using command line (Vista)?

  - by Amby

  Is there a way to start windows "explorer" process from command line? Because of some problem in my Vista OS, explorer process crashes frequently (i can not see TaskBar after that) but using the open windows i can access the cmd.exe ( ctrl+alt+delete does not work). If there could be a command to start "explorer" process again or to start the Task manager then that would help a lot. Thanks Edit: explorer command starts the explorer process, but alt+ctrl+del is still not working, any help?

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• How can I assign the keyboard shortcut ?x to the command move to trash?

  - by Fra

  In the Finder in Leopard I used to have the command "move to trash" associated with the keyboard shortcut ?x which was very handy because you could input the command with one hand. Moreover on the keyboard x is near to c, s and a which are other shortcuts often used in Finder. Now in Lion the command "move to trash" is associated to ? ? but I don't like it. How can I assign the keyboard shortcut ?x to the command "move to trash"?

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• How to solve "command not found" on Ubuntu bash shell?

  - by redcoder

  I am very new to Ubuntu, struggling to find the proper command to install Zend Server on my Ubuntu 9.10 Server. After downloading the ZF Server and extracting it, I try to run this command: install_zs.sh 5.3 This is the ls of the extracted ZF archive: install_zs.sh README upgrade_zs_php.sh zend.deb.repo zend.rpm.repo But it says command not found. Any idea?

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• How can I use '{}' to redirect the output of a command run through find's -exec option?

  - by pkaeding

  I am trying to automate an svnadmin dump command for a backup script, and I want to do something like this: find /var/svn/* \( ! -name dir -prune \) -type d -exec svnadmin dump {} > {}.svn \; This seems to work, in that it looks through each svn repository in /var/svn, and runs svnadmin dump on it. However, the second {} in the exec command doesn't get substituted for the name of the directory being processed. It basically just results a single file named {}.svn. I suspect that this is because the shell interprets > to end the find command, and it tries redirecting stdout from that command to the file named {}.svn. Any ideas?

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• Started an application through SSH, command line now gone, what happens next?

  - by Chris Dutrow

  Context: This is a very basic question Using Putty and SSH for the first time to do some serious server setup and run into the situation where I have started a process that I do not want to stop. The process is the gunicorn WSGI HTTP Server (running on Centos 6.3). The command I used to start the process is (as per their Quick Start): gunicorn -w 4 myapp:app At this point in the work session, I have lost the command prompt. This must be such a non-issue that it doesn't even enter into an experienced user's consciousness. But unfortunately at my level of experience, I am left with several fundamental questions: Does the fact that I have lost the command prompt mean that the process is still running? How do I get back to the command prompt without killing the process? How do I come back and monitor the process later? How do I eventually kill the process? Any help is appreciated, thanks so much!

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• How to execute a multiple line configure command using Mac OS X terminal?

  - by skiabox

  I am reading a nice article about upgrading php on mac os x mountain lion. At the Install part of the document the author says that the user must execute a multiple line configure command. What is the easiest way to do it, using mac os terminal? Thank you. PS : I have executed yesterday the configure command without the parameters. Can this action cause any problems with the re-execution of configure command (with parameters this time)?

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• Is it a "pattern smell" to put getters like "FullName" or "FormattedPhoneNumber" in your model?

  - by DanM

  I'm working on an ASP.NET MVC app, and I've been getting into the habit of putting what seem like helpful and convenient getters into my model/entity classes. For example: public class Member { public int Id { get; set; } public string FirstName { get; set; } public string LastName { get; set; } public string PhoneNumber { get; set; } public string FullName { get { return FirstName + " " + LastName; } } public string FormattedPhoneNumber { get { return "(" + PhoneNumber.Substring(0, 3) + ") " + PhoneNumber.Substring(3, 3) + "-" + PhoneNumber.Substring(6); } } } I'm wondering people think about the FullName and FormattedPhoneNumber getters. They make it very easy to create standardized data formats throughout the app, and they seem to save a lot of repeated code, but it could definitely be argued that data format is something that should be handled in mapping from model to view-model. In fact, I was originally applying these data formats in my service layer where I do my mapping, but it was becoming a burden to constantly have to write formatters then apply them in many different places. E.g., I use "Full Name" in most views, and having to type something like model.FullName = MappingUtilities.GetFullName(entity.FirstName, entity.LastName); all over the place seemed a lot less elegant than just typing model.FullName = entity.FullName (or, if you use something like AutoMapper, potentially not typing anything at all). So, where do you draw the line when it comes to data formatting. Is it "okay" to do data formatting in your model or is that a "pattern smell"? Note: I definitely do not have any html in my model. I use html helpers for that. I'm strictly talking about formatting or combining data (and especially data that is frequently used).

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• How to define type-specific scripts when using a 'type object' programming pattern?

  - by Erik

  I am in the process of creating a game engine written in C++, using the C/C++ SQLite interface to achieve a 'type object' pattern. The process is largely similar to what is outlined here (Thank you Bob Nystrom for the great resource!). I have a generally defined Entity class that when a new object is created, data is taken from a SQLite database and then is pushed back into a pointer vector, which is then iterated through, calling update() for each object. All the ints, floats, strings are loaded in fine, but the script() member of Entity is proving an issue. It's not much fun having a bunch of stationary objects laying around my gameworld. The only solutions I've come up with so far are: Create a monolithic EntityScript class with member functions encompassing all game AI and then calling the corresponding script when iterating through the Entity vector. (Not ideal) Create bindings between C++ and a scripting language. This would seem to get the job done, but it feels like implementing this (given the potential memory overhead) and learning a new language is overkill for a small team (2-3 people) that know the entirety of the existing game engine. Can you suggest any possible alternatives? My ideal situation would be that to add content to the game, one would simply add a script file to the appropriate directory and append the SQLite database with all the object data. All that is required is to have a variety of integers and floats passed between both the engine and the script file.

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• Can you point me to a nontrivial strategy pattern implementation?

  - by Eugen Martynov

  We are faced implementing a registration workflow with many branches. There are three main flows which in some conditions lead to one another. Each flow has at least four different steps; some steps interact with the server, and every step adds more information to the state. Also the requirement is to have it persistent between sessions, so if the user closes the app (this is a mobile app), it will restore the process from the last completed step with the state from the previous session. I think this could benefit from the use of the strategy pattern, but I've never had to implement it for such a complex case. Does anyone know of any examples in open source or articles from which I could find inspiration? Preferably the examples would be from a live/working/stable application. I'm interested in Java implementation mostly; we are developing for Java mobile phones: android, blackberry and J2ME. We have an SDK which is quite well separated from platform specific implementations, but examples in C++, C#, Objective-C or Python would be acceptable.

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• Is implementing an interface defined in a subpackage an anti-pattern?

  - by Michael Kjörling

  Let's say I have the following: package me.my.pkg; public interface Something { /* ... couple of methods go here ... */ } and: package me.my; import me.my.pkg.Something; public class SomeClass implements Something { /* ... implementation of Something goes here ... */ /* ... some more method implementations go here too ... */ } That is, the class implementing an interface lives closer to the package hierarchy root than does the interface it implements but they both belong in the same package hierarchy. The reason for this in the particular case I have in mind is that there is a previously-existing package that groups functionality which the Something interface logically belongs to, and the logical (as in both "the one you'd expect" and "the one where it needs to go given the current architecture") implementation class exists previously and lives one level "up" from the logical placement of the interface. The implementing class does not logically belong anywhere under me.my.pkg. In my particular case, the class in question implements several interfaces, but that feels like it doesn't make any (or at least no significant) difference here. I can't decide if this is an acceptable pattern or not. Is it or is it not, and why?

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• Can observer pattern be represented by cars and traffic lights?

  - by eeerahul

  I wanted to verify with all of you, if I have a correct Observer Pattern analogy. The scenario is as follows: Consider, at a junction, there is a traffic signal, having red, yellow and green lights respectively. There are vehicles facing the traffic signal post. When it shows red, the vehicles stop, when it shows green, the vehicles move on. In case, it is yellow, the driver must decide whether to go or to stop, depending on whether he/she has crossed the stop line or not. At the same time, there are vehicles that do not care about the signal. They would do as they like. The similarities are that, the Traffic Signal happens to be the subject, notifying its states by glowing the appropriate lights. Those looking at it and following the signal are the ones subscribed to it, and behave according to the state of the subject. Those who do not care about it, are sort-of un-subscribed from the traffic signal. Please tell me, if you think this is a correct analogy or not?

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• What is the preferred pattern when attaching a 'runtime object'?

  - by sebf

  In my application I have the following: public class NeatObject { /* lots of static data, and configuration flags */ } public class NeatObjectConsumer { void DoCleverStuffWithObjectOnGPU(NeatObject obj); } Where NeatObject and its consumer are used to control the GPU. The idea being that, the configuration of an instance of NeatObject and its members, define how the consumer instance behaves. The object can be passed around, edited, and most importantly serialised/deserialised by the application, with and without knowledge of NeatObjectConsumer, then provided back to the consumer to do something else. The purpose of this seperation is: The consumer manages hardware resources, which change depending on the computer, and even on the execution of the application, making preserving the state of an object which does everything difficult. Avoids circular references if the assembly that contains the consumer needs to reference one that only needs to know about NeatObject. However, there is a complication in that the consumer creates hardware resources and needs to associate them with NeatObject. These don't need to be preserved, but still need to be retrieved. DoCleverStuffWithObjectOnGPU() will be called many, many times during execution and so any bottleneck is a concern, therefore I would like to avoid dictionary lookups. What is the preferred method of attaching this information to NeatObject? By preferred, I mean intuitive - other coders can see immediately what is going on - and robust - method doesn't invite playing with the resources or present them in such a way as to make them easily corruptible. Essentially, I want to add my own metadata - how should I do it? Try to use 'actual metadata' functionality like Reflection? A member of the type of an abstract class? Unmanaged pointers? If you took on a project that used this pattern, what would you have liked the previous developer to do?

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• What design pattern (in python) to use for properly seperate runtime infos with core code?

  - by user1824372

  I am not sure if this is a clear question. I work on a python project that is based on terminal(console), for which I am planning to implement a GUI. I am not major in CS so I really have no idea about how to effectively design a message system such that: in console, it provide nice look info when runtime. in GUI, it is directed to a certain widget, let's say, a text label, or a bottom bar, or a hide-able frame. Do you have any suggestions? Currently, I am using print function to provide essential informations on stdout during runtime. So a lot of print .... are distributed here and there among the code. I am thinking to use macro-like variables such as 'FILE_NOT_EXTIS_MESSAGE' for printing, and define the variables in one file. Is this a standard way that people always do? How about I introduce a logging system? In sum, I am ask for a pattern that people are commonly using for handling of screen output information with high effectiveness and adaptivity.

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• Can I have a macro in Visual Studio 2005 call a DOS command and redirect the output to a file?

  - by Mark

  I'd like to have a macro in Visual Studio 2005 that calls a DOS command and redirects the output (stdout and stderr) to a file. Just calling the command and "" redirecting it will not capture stderr, so there are two parts to this: calling a DOS command capturing both stderr and stdout to a file during that call I'd then like to open this file in Visual Studio after the command completes. I'm new to Visual Studio 2005 macro writing, and VB/VBA, so that's the kind of help that I'm looking for. Thanks, Mark

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• Failing Sata HDD

  - by DaveCol

  I think my HDD is fried... Could someone confirm or help me restore it? I was using Hardware RAID 1 Configuration [2 x 160GB SATA HDD] on a CentOS 4 Installation. All of a sudden I started seeing bad sectors on the second HDD which stopped being mirrored. I have removed the RAID array and have tested with SMART which showed the following error: 187 Unknown_Attribute 0x003a 001 001 051 Old_age Always FAILING_NOW 4645 I have no clue what this means, or if I can recover from it. Could someone give me some ideas on how to fix this, or what HDD to get to replace this? Complete SMART report: Smartctl version 5.33 [i686-redhat-linux-gnu] Copyright (C) 2002-4 Bruce Allen Home page is http://smartmontools.sourceforge.net/ === START OF INFORMATION SECTION === Device Model: GB0160CAABV Serial Number: 6RX58NAA Firmware Version: HPG1 User Capacity: 160,041,885,696 bytes Device is: Not in smartctl database [for details use: -P showall] ATA Version is: 7 ATA Standard is: ATA/ATAPI-7 T13 1532D revision 4a Local Time is: Tue Oct 19 13:42:42 2010 COT SMART support is: Available - device has SMART capability. SMART support is: Enabled === START OF READ SMART DATA SECTION === SMART overall-health self-assessment test result: PASSED See vendor-specific Attribute list for marginal Attributes. General SMART Values: Offline data collection status: (0x82) Offline data collection activity was completed without error. Auto Offline Data Collection: Enabled. Self-test execution status: ( 0) The previous self-test routine completed without error or no self-test has ever been run. Total time to complete Offline data collection: ( 433) seconds. Offline data collection capabilities: (0x5b) SMART execute Offline immediate. Auto Offline data collection on/off support. Suspend Offline collection upon new command. Offline surface scan supported. Self-test supported. No Conveyance Self-test supported. Selective Self-test supported. SMART capabilities: (0x0003) Saves SMART data before entering power-saving mode. Supports SMART auto save timer. Error logging capability: (0x01) Error logging supported. General Purpose Logging supported. Short self-test routine recommended polling time: ( 2) minutes. Extended self-test routine recommended polling time: ( 54) minutes. SMART Attributes Data Structure revision number: 10 Vendor Specific SMART Attributes with Thresholds: ID# ATTRIBUTE_NAME FLAG VALUE WORST THRESH TYPE UPDATED WHEN_FAILED RAW_VALUE 1 Raw_Read_Error_Rate 0x000f 100 253 006 Pre-fail Always - 0 3 Spin_Up_Time 0x0002 097 097 000 Old_age Always - 0 4 Start_Stop_Count 0x0033 100 100 020 Pre-fail Always - 152 5 Reallocated_Sector_Ct 0x0033 095 095 036 Pre-fail Always - 214 7 Seek_Error_Rate 0x000f 078 060 030 Pre-fail Always - 73109713 9 Power_On_Hours 0x0032 083 083 000 Old_age Always - 15133 10 Spin_Retry_Count 0x0013 100 100 097 Pre-fail Always - 0 12 Power_Cycle_Count 0x0033 100 100 020 Pre-fail Always - 154 184 Unknown_Attribute 0x0032 038 038 000 Old_age Always - 62 187 Unknown_Attribute 0x003a 001 001 051 Old_age Always FAILING_NOW 4645 189 Unknown_Attribute 0x0022 100 100 000 Old_age Always - 0 190 Unknown_Attribute 0x001a 061 055 000 Old_age Always - 656408615 194 Temperature_Celsius 0x0000 039 045 000 Old_age Offline - 39 (Lifetime Min/Max 0/22) 195 Hardware_ECC_Recovered 0x0032 070 059 000 Old_age Always - 12605265 197 Current_Pending_Sector 0x0000 100 100 000 Old_age Offline - 1 198 Offline_Uncorrectable 0x0000 100 100 000 Old_age Offline - 0 199 UDMA_CRC_Error_Count 0x0000 200 200 000 Old_age Offline - 62 SMART Error Log Version: 1 ATA Error Count: 4645 (device log contains only the most recent five errors) CR = Command Register [HEX] FR = Features Register [HEX] SC = Sector Count Register [HEX] SN = Sector Number Register [HEX] CL = Cylinder Low Register [HEX] CH = Cylinder High Register [HEX] DH = Device/Head Register [HEX] DC = Device Command Register [HEX] ER = Error register [HEX] ST = Status register [HEX] Powered_Up_Time is measured from power on, and printed as DDd+hh:mm:SS.sss where DD=days, hh=hours, mm=minutes, SS=sec, and sss=millisec. It "wraps" after 49.710 days. Error 4645 occurred at disk power-on lifetime: 15132 hours (630 days + 12 hours) When the command that caused the error occurred, the device was active or idle. After command completion occurred, registers were: ER ST SC SN CL CH DH -- -- -- -- -- -- -- 40 51 00 7b 86 b1 ea Error: UNC at LBA = 0x0ab1867b = 179406459 Commands leading to the command that caused the error were: CR FR SC SN CL CH DH DC Powered_Up_Time Command/Feature_Name -- -- -- -- -- -- -- -- ---------------- -------------------- c8 00 02 7b 86 b1 ea 00 00:38:52.796 READ DMA ec 03 45 00 00 00 a0 00 00:38:52.796 IDENTIFY DEVICE ef 03 45 00 00 00 a0 00 00:38:52.794 SET FEATURES [Set transfer mode] ec 00 00 7b 86 b1 a0 00 00:38:49.991 IDENTIFY DEVICE c8 00 04 79 86 b1 ea 00 00:38:49.935 READ DMA Error 4644 occurred at disk power-on lifetime: 15132 hours (630 days + 12 hours) When the command that caused the error occurred, the device was active or idle. After command completion occurred, registers were: ER ST SC SN CL CH DH -- -- -- -- -- -- -- 40 51 00 7b 86 b1 ea Error: UNC at LBA = 0x0ab1867b = 179406459 Commands leading to the command that caused the error were: CR FR SC SN CL CH DH DC Powered_Up_Time Command/Feature_Name -- -- -- -- -- -- -- -- ---------------- -------------------- c8 00 04 79 86 b1 ea 00 00:38:41.517 READ DMA ec 03 45 00 00 00 a0 00 00:38:41.515 IDENTIFY DEVICE ef 03 45 00 00 00 a0 00 00:38:41.515 SET FEATURES [Set transfer mode] ec 00 00 7b 86 b1 a0 00 00:38:49.991 IDENTIFY DEVICE c8 00 06 77 86 b1 ea 00 00:38:49.935 READ DMA Error 4643 occurred at disk power-on lifetime: 15132 hours (630 days + 12 hours) When the command that caused the error occurred, the device was active or idle. After command completion occurred, registers were: ER ST SC SN CL CH DH -- -- -- -- -- -- -- 40 51 00 7b 86 b1 ea Error: UNC at LBA = 0x0ab1867b = 179406459 Commands leading to the command that caused the error were: CR FR SC SN CL CH DH DC Powered_Up_Time Command/Feature_Name -- -- -- -- -- -- -- -- ---------------- -------------------- c8 00 06 77 86 b1 ea 00 00:38:41.517 READ DMA ec 03 45 00 00 00 a0 00 00:38:41.515 IDENTIFY DEVICE ef 03 45 00 00 00 a0 00 00:38:41.515 SET FEATURES [Set transfer mode] ec 00 00 7b 86 b1 a0 00 00:38:41.513 IDENTIFY DEVICE c8 00 06 77 86 b1 ea 00 00:38:38.706 READ DMA Error 4642 occurred at disk power-on lifetime: 15132 hours (630 days + 12 hours) When the command that caused the error occurred, the device was active or idle. After command completion occurred, registers were: ER ST SC SN CL CH DH -- -- -- -- -- -- -- 40 51 00 7b 86 b1 ea Error: UNC at LBA = 0x0ab1867b = 179406459 Commands leading to the command that caused the error were: CR FR SC SN CL CH DH DC Powered_Up_Time Command/Feature_Name -- -- -- -- -- -- -- -- ---------------- -------------------- c8 00 06 77 86 b1 ea 00 00:38:41.517 READ DMA ec 03 45 00 00 00 a0 00 00:38:41.515 IDENTIFY DEVICE ef 03 45 00 00 00 a0 00 00:38:41.515 SET FEATURES [Set transfer mode] ec 00 00 7b 86 b1 a0 00 00:38:41.513 IDENTIFY DEVICE c8 00 06 77 86 b1 ea 00 00:38:38.706 READ DMA Error 4641 occurred at disk power-on lifetime: 15132 hours (630 days + 12 hours) When the command that caused the error occurred, the device was active or idle. After command completion occurred, registers were: ER ST SC SN CL CH DH -- -- -- -- -- -- -- 40 51 00 7b 86 b1 ea Error: UNC at LBA = 0x0ab1867b = 179406459 Commands leading to the command that caused the error were: CR FR SC SN CL CH DH DC Powered_Up_Time Command/Feature_Name -- -- -- -- -- -- -- -- ---------------- -------------------- c8 00 06 77 86 b1 ea 00 00:38:41.517 READ DMA ec 03 45 00 00 00 a0 00 00:38:41.515 IDENTIFY DEVICE ef 03 45 00 00 00 a0 00 00:38:41.515 SET FEATURES [Set transfer mode] ec 00 00 7b 86 b1 a0 00 00:38:41.513 IDENTIFY DEVICE c8 00 06 77 86 b1 ea 00 00:38:38.706 READ DMA SMART Self-test log structure revision number 1 Num Test_Description Status Remaining LifeTime(hours) LBA_of_first_error # 1 Short offline Completed without error 00% 15131 - # 2 Short offline Completed without error 00% 15131 - SMART Selective self-test log data structure revision number 1 SPAN MIN_LBA MAX_LBA CURRENT_TEST_STATUS 1 0 0 Not_testing 2 0 0 Not_testing 3 0 0 Not_testing 4 0 0 Not_testing 5 0 0 Not_testing Selective self-test flags (0x0): After scanning selected spans, do NOT read-scan remainder of disk. If Selective self-test is pending on power-up, resume after 0 minute delay.

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• Question about decorator pattern and the abstract decorator class?

  - by es11

  This question was asked already here, but rather than answering the specific question, descriptions of how the decorator pattern works were given instead. I'd like to ask it again because the answer is not immediately evident to me just by reading how the decorator pattern works (I've read the wikipedia article and the section in the book Head First Design Patterns). Basically, I want to know why an abstract decorator class must be created which implements (or extends) some interface (or abstract class). Why can't all the new "decorated classes" simply implement (or extend) the base abstract object themselves (instead of extending the abstract decorator class)? To make this more concrete I'll use the example from the design patterns book dealing with coffee beverages: There is an abstract component class called Beverage Simple beverage types such as HouseBlend simply extend Beverage To decorate beverage, an abstract CondimentDecorator class is created which extends Beverage and has an instance of Beverage Say we want to add a "milk" condiment, a class Milk is created which extends CondimentDecorator I'd like to understand why we needed the CondimentDecorator class and why the class Milk couldn't have simply extended the Beverage class itself and been passed an instance of Beverage in its constructor. Hopefully this is clear...if not I'd simply like to know why is the abstract decorator class necessary for this pattern? Thanks. Edit: I tried to implement this, omitting the abstract decorator class, and it seems to still work. Is this abstract class present in all descriptions of this pattern simply because it provides a standard interface for all of the new decorated classes?

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• Best Creational Pattern for loggers in a multi-threaded system?

  - by Dipan Mehta

  This is a follow up question on my past questions : Concurrency pattern of logger in multithreaded application As suggested by others, I am putting this question separately. As the learning from the last question. In a multi-threaded environment, the logger should be made thread safe and probably asynchronous (where in messages are queued while a background thread does writing releasing the requesting object thread). The logger could be signleton or it can be a per-group logger which is a generalization of the above. Now, the question that arise is how does logger should be assigned to the object? There are two options I can think of: 1. Object requesting for the logger: Should each of the object call some global API such as get_logger()? Such an API returns "the" singleton or the group logger. However, I feel this involves assumption about the Application environment to implement the logger -which I think is some kind of coupling. If the same object needs to be used by other application - this new application also need to implement such a method. 2. Assign logger through some known API The other alternative approach is to create a kind of virtual class which is implemented by application based on App's own structure and assign the object sometime in the constructor. This is more generalized method. Unfortunately, when there are so many objects - and rather a tree of objects passing on the logger objects to each level is quite messy. My question is there a better way to do this? If you need to pick any one of the above, which approach is would you pick and why? Other questions remain open about how to configure them: How do objects' names or ID are assigned so that will be used for printing on the log messages (as the module names) How do these objects find the appropriate properties (such as log levels, and other such parameters) In the first approach, the central API needs to deal with all this varieties. In the second approach - there needs to be additional work. Hence, I want to understand from the real experience of people, as to how to write logger effectively in such an environment.

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• What is a useful pattern to maintaining an object state in a one to many relationship?

  - by ahenderson

  I am looking for a design for my application, here are the players(classes) involved. struct Transform { // Uses a matrix to transform the position. // Also acts acts as the state of a Dialog. Position transform(Position p); //other methods. }; struct Dialog { // There are multiple dialog for the user to transform the output. Transform& t; void ChangeTranformation(){t.rotate(360);} } struct Algorithm { //gives us a position based on an implementation. For example this can return points on a circle or line. Transform& t; Position m_p; Dialog& d; Position GetCurrentPosition(){ return t.transform(m_p);} //other methods. } Properties I need: Each algorithms has one dialog and each dialog can have many algorithms associated with it. When the user selects an algorithm a dialog associated with that algorithm is displayed. If the user selects a different algorithm then re-selects back the state is restored in the dialog. Basically I want a good design pattern to maintain the state of the dialog given that many algorithms use it and they can be switched back and forth. Does anyone have any suggestions? Here is a use case: Dialog1 has a single edit box to control the radius. Algorithm1 generates points on a unit circle. Algorithm2 is the same as Algorithm1. The user has selected Algorithm1 and entered 2 into the edit box. This will generate points on a circle of radius 2. The user then selects Algorithm2 and enters 10 into the edit box of Dialog1. This will generate points on a circle of radius 10. Finally Algorithm1 is selected again. The edit box of Dialog1 should show 2 and points on a circle of radius 2 should be generated.

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• Is there a factory pattern to prevent multiple instances for same object (instance that is Equal) good design?

  - by dsollen

  I have a number of objects storing state. There are essentially two types of fields. The ones that uniquely define what the object is (what node, what edge etc), and the others that store state describing how these things are connected (this node is connected to these edges, this edge is part of these paths) etc. My model is updating the state variables using package methods, so all these objects act as immutable to anyone not in Model scope. All Objects extend one base type. I've toyed with the idea of a Factory approach which accepts a Builder object and constructs the applicable object. However, if an instance of the object already exists (ie would return true if I created the object defined by the builder and passed it to the equal method for the existing instance) the factory returns the current object instead of creating a new instance. Because the Equal method would only compare what uniquely defines the type of object (this is node A to node B) but won't check the dynamic state stuff (node A is currently connected to nodes C and E) this would be a way of ensuring anyone that wants my Node A automatically knows its state connections. More importantly it would prevent aliasing nightmares of someone trying to pass an instance of node A with different state then the node A in my model has. I've never heard of this pattern before, and it's a bit odd. I would have to do some overriding of serialization methods to make it work (ensure that when I read in a serilized object I add it to my facotry list of known instances, and/or return an existing factory in its place), as well as using a weakHashMap as if it was a weakHashSet to know whether an instance exists without worrying about a quasi-memory leak occuring. I don't know if this is too confusing or prone to its own obscure bugs. One thing I know is that plugins interface with lowest level hardware. The plugins have to be able to return state that is different than my memory; to tell my memory when its own state is inconsistent. I believe this is possible despite their fetching objects that exist in my memory; we allow building of objects without checking their consistency with the model until the addToModel is called anyways; and the existing plugins design was written before all this extra state existed and worked fine without ever being aware of it. Should I just be using some other design to avoid this crazyness? (I have another question to that affect that I'm posting).

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• How can you tell whether to use Composite Pattern or a Tree Structure, or a third implementation?

  - by Aske B.

  I have two client types, an "Observer"-type and a "Subject"-type. They're both associated with a hierarchy of groups. The Observer will receive (calendar) data from the groups it is associated with throughout the different hierarchies. This data is calculated by combining data from 'parent' groups of the group trying to collect data (each group can have only one parent). The Subject will be able to create the data (that the Observers will receive) in the groups they're associated with. When data is created in a group, all 'children' of the group will have the data as well, and they will be able to make their own version of a specific area of the data, but still linked to the original data created (in my specific implementation, the original data will contain time-period(s) and headline, while the subgroups specify the rest of the data for the receivers directly linked to their respective groups). However, when the Subject creates data, it has to check if all affected Observers have any data that conflicts with this, which means a huge recursive function, as far as I can understand. So I think this can be summed up to the fact that I need to be able to have a hierarchy that you can go up and down in, and some places be able to treat them as a whole (recursion, basically). Also, I'm not just aiming at a solution that works. I'm hoping to find a solution that is relatively easy to understand (architecture-wise at least) and also flexible enough to be able to easily receive additional functionality in the future. Is there a design pattern, or a good practice to go by, to solve this problem or similar hierarchy problems? EDIT: Here's the design I have: The "Phoenix"-class is named that way because I didn't think of an appropriate name yet. But besides this I need to be able to hide specific activities for specific observers, even though they are attached to them through the groups. A little Off-topic: Personally, I feel that I should be able to chop this problem down to smaller problems, but it escapes me how. I think it's because it involves multiple recursive functionalities that aren't associated with each other and different client types that needs to get information in different ways. I can't really wrap my head around it. If anyone can guide me in a direction of how to become better at encapsulating hierarchy problems, I'd be very glad to receive that as well.

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• is a factory pattern to prevent multuple instances for same object (instance that is Equal) good design?

  - by dsollen

  I have a number of objects storing state. There are essentially two types of fields. The ones that uniquly define what the object is (what node, what edge etc), and the oens that store state describing how these things are connected (this node is connected to these edges, this edge is part of these paths) etc. My model is updating the state variables using package methdos, so these objects all act as immutable to anyone not in Model scope. All Objects extend one base type. I've toyed with the idea of a Factory approch which accepts a Builder object and construct the applicable object. However, if an instance of the object already exists (ie would return true if I created the object defined by the builder and passed it to the equal method for the existing instance) the factory returns the current object instead of creating a new instance. Because the Equal method would only compare what uniquly defines the type of object (this is node A nto node B) but won't check the dynamic state stuff (node A is currently connected to nodes C and E) this would be a way of ensuring anyone that wants my Node A automatically knows it's state connections. More importantly it would prevent aliasing nightmares of someone trying to pass an instance of node A with different state then the node A in my model has. I've never heard of this pattern before, and it's a bit odd. I would have to do some overiding of serlization methods to make it work (ensure when I read in a serilized object I add it to my facotry list of known instances, and/or return an existing factory in it's place), as well as using a weakHashMap as if it was a weakHashSet to know rather an instance exists without worrying about a quasi-memory leak occuring. I don't know if this is too confusing or prone to it's own obscure bugs. One thing I know is that plugins interface with lowest level hardware. The plugins have to be able to return state taht is different then my memory; to tell my memory when it's own state is inconsistent. I believe this is possible despit their fetching objects that exist in my memory; we allow building of objects without checking their consistency with the model until the addToModel is called anyways; and the existing plugins design was written before all this extra state existed and worked fine without ever being aware of it. Should I just be using some other design to avoid this crazyness? (I have another question to that affect I'm posting).

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• Architecture or Pattern for handling properties with custom setter/getter?

  - by Shelby115

  Current Situation: I'm doing a simple MVC site for keeping journals as a personal project. My concern is I'm trying to keep the interaction between the pages and the classes simplistic. Where I run into issues is the password field. My setter encrypts the password, so the getter retrieves the encrypted password. public class JournalBook { private IEncryptor _encryptor { get; set; } private String _password { get; set; } public Int32 id { get; set; } public String name { get; set; } public String description { get; set; } public String password { get { return this._password; } set { this.setPassword(this._password, value, value); } } public List<Journal> journals { get; set; } public DateTime created { get; set; } public DateTime lastModified { get; set; } public Boolean passwordProtected { get { return this.password != null && this.password != String.Empty; } } ... } I'm currently using model-binding to submit changes or create new JournalBooks (like below). The problem arises that in the code below book.password is always null, I'm pretty sure this is because of the custom setter. [HttpPost] public ActionResult Create(JournalBook book) { // Create the JournalBook if not null. if (book != null) this.JournalBooks.Add(book); return RedirectToAction("Index"); } Question(s): Should I be handling this not in the property's getter/setter? Is there a pattern or architecture that allows for model-binding or another simple method when properties need to have custom getters/setters to manipulate the data? To summarize, how can I handle the password storing with encryption such that I have the following, Robust architecture I don't store the password as plaintext. Submitting a new or modified JournalBook is as easy as default model-binding (or close to it).

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