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• PHP - Internal APIs/Libraries - What makes sense?

  - by Mark Locker

  I've been having a discussion lately with some colleagues about the best way to approach a new project, and thought it'd be interesting to get some external thoughts thrown into the mix. Basically, we're redeveloping a fairly large site (written in PHP) and have differing opinions on how the platform should be setup. Requirements: The platform will need to support multiple internal websites, as well as external (non-PHP) projects which at the moment consist of a mobile app and a toolbar. We have no plans/need in the foreseeable future to open up an API externally (for use in products other than our own). My opinion: We should have a library of well documented native model classes which can be shared between projects. These models will represent everything in our database and can take advantage of object orientated features such as inheritance, traits, magic methods, etc. etc. As well as employing ORM. We can then add an API layer on top of these models which can basically accept requests and route them to the appropriate methods, translating the response so that it can be used platform independently. This routing for each method can be setup as and when it's required. Their opinion: We should have a single HTTP API which is used by all projects (internal PHP ones or otherwise). My thoughts: To me, there are a number of issues with using the sole HTTP API approach: It will be very expensive performance wise. One page request will result in several additional http requests (which although local, are still ones that Apache will need to handle). You'll lose all of the best features PHP has for OO development. From simple inheritance, to employing the likes of ORM which can save you writing a lot of code. For internal projects, the actual process makes me cringe. To get a users name, for example, a request would go out of our box, over the LAN, back in, then run through a script which calls a method, JSON encodes the output and feeds that back. That would then need to be JSON decoded, and be presented as an array ready to use. Working with arrays, as appose to objects, makes me sad in a modern PHP framework. Their thoughts (and my responses): Having one method of doing thing keeps things simple. - You'd only do things differently if you were using a different language anyway. It will become robust. - Seeing as the API will run off the library of models, I think my option would be just as robust. What do you think? I'd be really interested to hear the thoughts of others on this, especially as opinions on both sides are not founded on any past experience.

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• Polygon count budget

  - by Lautaro

  Is there any smart way to think about polygon budget relating to PC gaming today? My game will have one static 3d background scene and two fighters. No more enemies. I am thinking about having animated 3d models in the background for atmosphere, like spectators. So how could i find out what the polygon count for the player models and background scenarios could be. I guess the question is, what is a for today typical polygon count that most PCs can handle?

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• build SQL query string using user input

  - by user175084

  i have to make a string by using the values which the user selects on the webpage suppose i need to display files for multiple machines with differnt search criteria.. i currently use this code: DataTable dt = new DataTable(); SqlConnection connection = new SqlConnection(); connection.ConnectionString = ConfigurationManager.ConnectionStrings["DBConnectionString"].ConnectionString; connection.Open(); SqlCommand sqlCmd = new SqlCommand("SELECT FileID FROM Files WHERE MachineID=@machineID and date= @date", connection); SqlDataAdapter sqlDa = new SqlDataAdapter(sqlCmd); sqlCmd.Parameters.AddWithValue("@machineID", machineID); sqlCmd.Parameters.AddWithValue("@date", date); sqlDa.Fill(dt); now this is fixed query where the user just has one machine and just selects one date... i want to make a query in which the user has multiple search options like type or size if he wants depending on what he selects also if he can select multiple machines.. SELECT FileID FROM Files WHERE (MachineID=@machineID1 or MachineID = @machineID2...) and (date= @date and size=@size and type=@type... ) all of this happens in runtime... other wise i have to create a for loop to put multiple machines one by one... and have multiple queries depending on the case the user selected... this is quiet interesting and i could use some help... thanks

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• Demand for Pay-per-Use Software Pricing Will Force a Reassessment of the Industry's Framework

  IDC reports that SaaS and cloud computing models are feeding the demand for pay-per-use software pricing.

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• 2-components color model

  - by Cyan

  RGB is the natural color model for OpenGL. But a lot of other color models exist. For example, CMY(K) for printers, YUV for JPEG, the little cousins YCbCr and YCoCg, HSL & HSV from the 70's, and so on. All these models tend to share a common property : they are based on 3 components. Therefore my question is : Does it exist a 2-components color model ? I'm surprised to not find any. I was expecting something along the line of Hue+light could exist. I guess it cannot be as "complete" as a true 3-components color model, but a fine-enough approximation will be good for my usecase. The end objective is to store the 2 components into a single BC5 texture (GL_COMPRESSED_RED_GREEN_RGTC2 in OpenGL). The 3rd component requires a second fetch into a second texture, which hurts performance.

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• To check the default select value tag!

  - by Small Wolf

  I have a question.Here is the code! f.select(:departments,Department.all.collect{|c|[c.name,c.id]},{},:size=>10,:multiple => ture) class Emergency has many :departments end the html source like this: <select id="emergency_departments" multiple="multiple" name="emergency[departments][]" size="10"><option value ="">""</option>....</select> now I want to get the default selected tag , who can tell me how ?

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• javax.crypto AES encryption - Do I only need to call doFinal?

  - by Spines

  I want to do AES CBC encryption in Java. I'm using javax.crypto. After I have the Cipher initialized, do I only need to call doFinal on the clear bytes to properly encrypt it? Or do I need to do something with update? Documentation says update: Continues a multiple-part encryption or decryption operation and doFinal Encrypts or decrypts data in a single-part operation, or finishes a multiple-part operation what exactly do they mean by multiple-part encryption?

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• Hibernate Query - Get latest versions by timestamp?

  - by Slim

  I have a database that is being used as a sort of version control system. That is, instead of ever updating any rows, I add a new row with the same information. Each row also contains a version column that is a date timestamp, so the only difference is the new row will have a more recent timestamp. What I'm having trouble with is writing an efficient hibernate query to return the latest version of these rows. For the sake of example, these are rows in a table called Product, the timestamped column is version. There are multiple versions of multiple products in the table. So there may be multiple versions (rows) of ProductA, multiple versions of ProductB, etc. And I would like to grab the latest version of each. Can I do this in just a single hibernate query? session.createQuery("select product from Product product where...?"); Or would this require some intermediate steps?

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• Search and Replace in MVC

  - by danip

  What would be a good MVC/OOP/GRASP/SOLID structure for a search/replace functionality. Methods: search/searchNext/replace/replaceAll. I'm interested only in the PHP arhitecture and how a professional developer would implement this in it's OWN FRAMEWORK. What names would you use for the classes? What subfolders would you used in your MODEL folder? How would you connect the MODELS/CONTROLLER? This is just a arhitecture question to understand better the principles of good OOP in practice. My current implementation is very simplistic using a service model: /controller/SearchReplaceController.php /models/services/SearchReplaceService.php The problem with this is I know I'm breaking SRP in the service but I found this somehow acceptable. Also creating a service does not feel like the best solution for this.

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• Using The Data Mining Query Task in SSIS

  The Data Mining Query Task can be used to run prediction queries based on data mining models built in analysis service.

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• New Seagate SSD and Hard Disks

  - by jchang

  Seagate today announced a near complete overhaul of their enterprise product line. This include second generation SSD now with either SAS and SATA interfaces. The first generation Pulsar SSD only supported SATA interface. The new 2.5in 15K and 10K hard drive models have higher capacity. The 2.5in 7.2K hard drive was upgraded to 1TB last month? The 7.2K 3.5in is now available upto 3TB. All models support 6Gbps. The new second generation Seagate Pulsar SSD comprises two product lines. The Pulsar XT.2...(read more)

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• Can I play any Buffer only once at a given time?

  - by mystify

  From the OpenAL documentation: The basic OpenAL objects are a Listener, a Source, and a Buffer. There can be a large number of Buffers, which contain audio data. Each buffer can be attached to one or more Sources My problem is, that I have one sound file which I need to play multiple times per second, at the same time. The sound is 2 seconds long. So it will overlap. Would I need multiple filled buffers for this (= multiple times that sound in memory)? If I would attach one Buffer to multiple Sources, would I be able to play the sound 10 times, overlapping itself, with just one copy in memory? Or would I still have to deal with 10 copies of that sound in memory?

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• How to get warning massage when clicking close(X) button of browser with tabs in Google Crome

  - by Shantanu

  How to get a warning massage if i accidently click the close button of the chrome browser which have multiple tabs opened at that time? I am a regular user of Crome and having this problem while using it. I normally open multiple tabs inside a single browser but sometimes i accidently click the close button of browser and as soon as the button is clicked crome does't give any warning issue about multiple active tabs and close the entire window. Is the end user like me is browsing on normal crome window then he can open the websites again by checking the web history but if he is browsing inside private browser then he can't do anything(this happens with me very regularly because i normally browse in private browser). On the other hand if you accidently click the close button in mozilla which have multiple tabs open it throws a warning massage to the user and asks for his wish.

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• Images missing after moving Django to new server

  - by miszczu

  I'm moving Django project to new server. I'm newbie in Django, and I don't know where should be upload folder. There are all images which should be displayed on website. In config file I haven't seen upload folder I could specify, so I'm guessing it always should be the same location for django projects or I just can't find it. Locations are saved in database. When I've put uploaded files into media folder, so url was like domain.co.uk/media/upload/media/images/year/month/day/image_name.ext and the same is on the old website, images on website ware still missing. All images are visible if I put url by hand, but django doesn't seems to see files. Also I check django log file: 2012-05-30 09:13:33,393 ERROR render: Thumbnail tag failed: [in /usr/lib/python2.6/site-packages/sorl_thumbnail-11.12-py2.6.egg/sorl/thumbnail/templatetags/thumbnail.py (line 49)] Traceback (most recent call last): File "/usr/lib/python2.6/site-packages/sorl_thumbnail-11.12-py2.6.egg/sorl/thumbnail/templatetags/thumbnail.py", line 45, in render return self._render(context) File "/usr/lib/python2.6/site-packages/sorl_thumbnail-11.12-py2.6.egg/sorl/thumbnail/templatetags/thumbnail.py", line 97, in _render file_, geometry, **options File "/usr/lib/python2.6/site-packages/sorl_thumbnail-11.12-py2.6.egg/sorl/thumbnail/base.py", line 50, in get_thumbnail cached = default.kvstore.get(thumbnail) File "/usr/lib/python2.6/site-packages/sorl_thumbnail-11.12-py2.6.egg/sorl/thumbnail/kvstores/base.py", line 25, in get return self._get(image_file.key) File "/usr/lib/python2.6/site-packages/sorl_thumbnail-11.12-py2.6.egg/sorl/thumbnail/kvstores/base.py", line 123, in _get value = self._get_raw(add_prefix(key, identity)) File "/usr/lib/python2.6/site-packages/sorl_thumbnail-11.12-py2.6.egg/sorl/thumbnail/kvstores/cached_db_kvstore.py", line 26, in _get_raw value = KVStoreModel.objects.get(key=key).value File "/usr/lib/python2.6/site-packages/django/db/models/manager.py", line 132, in get return self.get_query_set().get(*args, **kwargs) File "/usr/lib/python2.6/site-packages/django/db/models/query.py", line 344, in get num = len(clone) File "/usr/lib/python2.6/site-packages/django/db/models/query.py", line 82, in __len__ self._result_cache = list(self.iterator()) File "/usr/lib/python2.6/site-packages/django/db/models/query.py", line 273, in iterator for row in compiler.results_iter(): File "/usr/lib/python2.6/site-packages/django/db/models/sql/compiler.py", line 680, in results_iter for rows in self.execute_sql(MULTI): File "/usr/lib/python2.6/site-packages/django/db/models/sql/compiler.py", line 735, in execute_sql cursor.execute(sql, params) File "/usr/lib/python2.6/site-packages/django/db/backends/util.py", line 34, in execute return self.cursor.execute(sql, params) File "/usr/lib/python2.6/site-packages/django/db/backends/mysql/base.py", line 86, in execute return self.cursor.execute(query, args) File "/usr/lib64/python2.6/site-packages/MySQLdb/cursors.py", line 174, in execute self.errorhandler(self, exc, value) File "/usr/lib64/python2.6/site-packages/MySQLdb/connections.py", line 36, in defaulterrorhandler raise errorclass, errorvalue DatabaseError: (1146, "Table 'thumbnail_kvstore' doesn't exist") 2012-05-30 09:13:33,396 DEBUG execute: (0.000) SELECT `freetext_freetext`.`id`, `freetext_freetext`.`key`, `freetext_freetext`.`content`, `freetext_freetext`.`active` FROM `freetext_freetext` WHERE (`freetext_freetext`.`active` = True AND `freetext_freetext`.`key` = office-closed-message ); args=(True, u'office-closed-message') [in /usr/lib/python2.6/site-packages/django/db/backends/util.py (line 44)] 2012-05-30 09:13:33,399 DEBUG execute: (0.000) SELECT `menus_menu`.`id`, `menus_menu`.`name`, `menus_menu`.`slug`, `menus_menu`.`base_url`, `menus_menu`.`description`, `menus_menu`.`enabled` FROM `menus_menu` WHERE (`menus_menu`.`enabled` = True AND `menus_menu`.`slug` = about ); args=(True, u'about') [in /usr/lib/python2.6/site-packages/django/db/backends/util.py (line 44)] 2012-05-30 09:13:33,401 DEBUG execute: (0.000) SELECT `menus_menuitem`.`id`, `menus_menuitem`.`menu_id`, `menus_menuitem`.`title`, `menus_menuitem`.`url`, `menus_menuitem`.`order` FROM `menus_menuitem` INNER JOIN `menus_menu` ON (`menus_menuitem`.`menu_id` = `menus_menu`.`id`) WHERE `menus_menu`.`slug` = about ORDER BY `menus_menuitem`.`order` ASC; args=(u'about',) [in /usr/lib/python2.6/site-packages/django/db/backends/util.py (line 44)] 2012-05-30 09:13:33,404 DEBUG execute: (0.000) SELECT `freetext_freetext`.`id`, `freetext_freetext`.`key`, `freetext_freetext`.`content`, `freetext_freetext`.`active` FROM `freetext_freetext` WHERE (`freetext_freetext`.`active` = True AND `freetext_freetext`.`key` = contactdetails-footer ); args=(True, u'contactdetails-footer') [in /usr/lib/python2.6/site-packages/django/db/backends/util.py (line 44)] I checked database and there is no table calls thumbnail_kvstore, but I have database backup, and in backup files this table doesn't exist. All uploaded files I get are in media/uploads/media/. Also I'm getting errors on some pages: Syntax error. Expected: ``thumbnail source geometry [key1=val1 key2=val2...] as var`` /usr/lib/python2.6/site-packages/sorl_thumbnail-11.12-py2.6.egg/sorl/thumbnail/templatetags/thumbnail.py in __init__, line 72 In template /var/www/vhosts/domain.co.uk/sites/apps/shop/products/templates/products/product_detail.html, error at line 34 {% thumbnail image.file "800x700" detail as zoom %} Maybe some modules I install are not in the right version. Dont know how to fix it. Im using, CentOS 6, mod_wsgi, apache, python 2.6. Update 1.0: On the old server was Django 1.3, on the new one is Django 1.3.1 Update 1.1: I this i know where is the problem. I tried python manage.py syncdb and this is output: Syncing... Creating tables ... The following content types are stale and need to be deleted: orders | ordercontact Any objects related to these content types by a foreign key will also be deleted. Are you sure you want to delete these content types? If you're unsure, answer 'no'. Type 'yes' to continue, or 'no' to cancel: no Installing custom SQL ... Installing indexes ... No fixtures found. Synced: > django.contrib.auth > django.contrib.contenttypes > django.contrib.sessions > django.contrib.sites > django.contrib.messages > django.contrib.admin > django.contrib.admindocs > django.contrib.markup > django.contrib.sitemaps > django.contrib.redirects > django_filters > freetext > sorl.thumbnail > django_extensions > south > currencies > pagination > tagging > honeypot > core > faq > logentry > menus > news > shop > shop.cart > shop.orders Not synced (use migrations): - dbtemplates - contactform - links - media - pages - popularity - testimonials - shop.brands - shop.collections - shop.discount - shop.pricing - shop.product_types - shop.products - shop.shipping - shop.tax (use ./manage.py migrate to migrate these) Next I run python manage.py migrate, and thats what i get: Running migrations for dbtemplates: - Migrating forwards to 0002_auto__del_unique_template_name. > dbtemplates:0001_initial ! Error found during real run of migration! Aborting. ! Since you have a database that does not support running ! schema-altering statements in transactions, we have had ! to leave it in an interim state between migrations. ! You *might* be able to recover with: = DROP TABLE `django_template` CASCADE; [] = DROP TABLE `django_template_sites` CASCADE; [] ! The South developers regret this has happened, and would ! like to gently persuade you to consider a slightly ! easier-to-deal-with DBMS. ! NOTE: The error which caused the migration to fail is further up. Traceback (most recent call last): File "manage.py", line 13, in <module> execute_manager(settings) File "/usr/lib/python2.6/site-packages/django/core/management/__init__.py", line 438, in execute_manager utility.execute() File "/usr/lib/python2.6/site-packages/django/core/management/__init__.py", line 379, in execute self.fetch_command(subcommand).run_from_argv(self.argv) File "/usr/lib/python2.6/site-packages/django/core/management/base.py", line 191, in run_from_argv self.execute(*args, **options.__dict__) File "/usr/lib/python2.6/site-packages/django/core/management/base.py", line 220, in execute output = self.handle(*args, **options) File "/usr/lib/python2.6/site-packages/South-0.7.3-py2.6.egg/south/management/commands/migrate.py", line 105, in handle ignore_ghosts = ignore_ghosts, File "/usr/lib/python2.6/site-packages/South-0.7.3-py2.6.egg/south/migration/__init__.py", line 191, in migrate_app success = migrator.migrate_many(target, workplan, database) File "/usr/lib/python2.6/site-packages/South-0.7.3-py2.6.egg/south/migration/migrators.py", line 221, in migrate_many result = migrator.__class__.migrate_many(migrator, target, migrations, database) File "/usr/lib/python2.6/site-packages/South-0.7.3-py2.6.egg/south/migration/migrators.py", line 292, in migrate_many result = self.migrate(migration, database) File "/usr/lib/python2.6/site-packages/South-0.7.3-py2.6.egg/south/migration/migrators.py", line 125, in migrate result = self.run(migration) File "/usr/lib/python2.6/site-packages/South-0.7.3-py2.6.egg/south/migration/migrators.py", line 99, in run return self.run_migration(migration) File "/usr/lib/python2.6/site-packages/South-0.7.3-py2.6.egg/south/migration/migrators.py", line 81, in run_migration migration_function() File "/usr/lib/python2.6/site-packages/South-0.7.3-py2.6.egg/south/migration/migrators.py", line 57, in <lambda> return (lambda: direction(orm)) File "/usr/lib/python2.6/site-packages/django_dbtemplates-1.3-py2.6.egg/dbtemplates/migrations/0001_initial.py", line 18, in forwards ('last_changed', self.gf('django.db.models.fields.DateTimeField')(default=datetime.datetime.now)), File "/usr/lib/python2.6/site-packages/South-0.7.3-py2.6.egg/south/db/generic.py", line 226, in create_table ', '.join([col for col in columns if col]), File "/usr/lib/python2.6/site-packages/South-0.7.3-py2.6.egg/south/db/generic.py", line 150, in execute cursor.execute(sql, params) File "/usr/lib/python2.6/site-packages/django/db/backends/util.py", line 34, in execute return self.cursor.execute(sql, params) File "/usr/lib/python2.6/site-packages/django/db/backends/mysql/base.py", line 86, in execute return self.cursor.execute(query, args) File "/usr/lib64/python2.6/site-packages/MySQLdb/cursors.py", line 174, in execute self.errorhandler(self, exc, value) File "/usr/lib64/python2.6/site-packages/MySQLdb/connections.py", line 36, in defaulterrorhandler raise errorclass, errorvalue _mysql_exceptions.OperationalError: (1050, "Table 'django_template' already exists") Also i run python manage.py migrate --list, and uotput is: dbtemplates (*) 0001_initial (*) 0002_auto__del_unique_template_name contactform (*) 0001_initial (*) 0002_auto__add_callback (*) 0003_auto__add_field_callback_notes (*) 0004_auto__add_field_callback_is_closed__add_field_callback_closed (*) 0005_auto__add_field_callback_url (*) 0006_auto__add_contact (*) 0007_auto__add_field_contact_category (*) 0008_auto__add_field_contact_url links (*) 0001_initial (*) 0002_auto__add_field_category_enabled__add_field_category_order media (*) 0001_initial (*) 0002_auto__del_field_image_external_url__add_field_image_link_url__del_fiel (*) 0003_add_model_FileAttachment (*) 0004_auto__chg_field_file_slug__chg_field_image_slug (*) 0005_auto__chg_field_image_file (*) 0006_auto__chg_field_file_file pages (*) 0001_initial (*) 0002_auto__chg_field_page_meta_description__chg_field_page_meta_title__chg_ (*) 0003_auto__add_field_page_show_in_sitemap (*) 0004_auto__add_field_page_changefreq__add_field_page_priority popularity (*) 0001_initial testimonials (*) 0001_initial (*) 0002_auto__add_field_testimonial_is_featured brands (*) 0001_initial (*) 0002_auto__add_field_brand_template (*) 0003_auto__chg_field_brand_meta_description__chg_field_brand_meta_title__ch (*) 0004_auto__add_field_brand_url (*) 0005_auto__del_field_brand_image__add_field_brand_logo collections (*) 0001_initial (*) 0002_auto__add_field_collection_discount (*) 0003_auto__chg_field_collection_meta_description__chg_field_collection_meta (*) 0004_auto__add_field_collection_is_featured (*) 0005_auto__add_field_collection_order discount (*) 0001_initial (*) 0002_added_field_discount_description (*) 0003_auto__add_field_discountvoucher_automatic (*) 0004_auto__add_field_discountvoucher_collection (*) 0005_auto__del_field_discountvoucher_collection (*) 0006_auto__chg_field_discountvoucher_expiry_date pricing (*) 0001_initial (*) 0002_auto__add_pricingrule product_types (*) 0001_initial (*) 0002_auto__add_field_producttype_meta_title__add_field_producttype_meta_des (*) 0003_auto__add_field_producttype_summary__add_field_producttype_description products (*) 0001_initial (*) 0002_auto__del_field_product_is_featured (*) 0003_auto__chg_field_product_meta_keywords__chg_field_product_meta_descript (*) 0004_auto shipping (*) 0001_initial (*) 0002_auto__add_field_shippingmethod_includes_tax__add_field_shippingmethod_ (*) 0003_auto__add_field_shippingmethod_order (*) 0004_auto__del_field_shippingmethod_tax_rate__del_field_shippingmethod_incl (*) 0005_auto__del_field_shippingrule_enabled tax (*) 0001_initial (*) 0002_auto__add_field_taxrate_internal_name (*) 0003_initial_internal_names (*) 0004_auto__add_unique_taxrate_internal_name (*) 0005_force_unique_taxrate_name (*) 0006_auto__add_unique_taxrate_name After that some images source were something like this: src="cache/1e/bd/1ebd719910aa843238028edd5fe49e71.jpg" Is any1 could help me with syncdb pledase?

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• Distributed and/or Parallel SSIS processing

  - by Jeff

  Background: Our company hosts SaaS DSS applications, where clients provide us data Daily and/or Weekly, which we process & merge into their existing database. During business hours, load in the servers are pretty minimal as it's mostly users running simple pre-defined queries via the website, or running drill-through reports that mostly hit the SSAS OLAP cube. I manage the IT Operations Team, and so far this has presented an interesting "scaling" issue for us. For our daily-refreshed clients, the server is only "busy" for about 4-6 hrs at night. For our weekly-refresh clients, the server is only "busy" for maybe 8-10 hrs per week! We've done our best to use some simple methods of distributing the load by spreading the daily clients evenly among the servers such that we're not trying to process daily clients back-to-back over night. But long-term this scaling strategy creates two notable issues. First, it's going to consume a pretty immense amount of hardware that sits idle for large periods of time. Second, it takes significant Production Support over-head to basically "schedule" the ETL such that they don't over-lap, and move clients/schedules around if they out-grow the resources on a particular server or allocated time-slot. As the title would imply, one option we've tried is running multiple SSIS packages in parallel, but in most cases this has yielded VERY inconsistent results. The most common failures are DTExec, SQL, and SSAS fighting for physical memory and throwing out-of-memory errors, and ETLs running 3,4,5x longer than expected. So from my practical experience thus far, it seems like running multiple ETL packages on the same hardware isn't a good idea, but I can't be the first person that doesn't want to scale multiple ETLs around manual scheduling, and sequential processing. One option we've considered is virtualizing the servers, which obviously doesn't give you any additional resources, but moves the resource contention onto the hypervisor, which (from my experience) seems to manage simultaneous CPU/RAM/Disk I/O a little more gracefully than letting DTExec, SQL, and SSAS battle it out within Windows. Question to the forum: So my question to the forum is, are we missing something obvious here? Are there tools out there that can help manage running multiple SSIS packages on the same hardware? Would it be more "efficient" in terms of parallel execution if instead of running DTExec, SQL, and SSAS same machine (with every machine running that configuration), we run in pairs of three machines with SSIS running on one machine, SQL on another, and SSAS on a third? Obviously that would only make sense if we could process more than the three ETL we were able to process on the machine independently. Another option we've considered is completely re-architecting our SSIS package to have one "master" package for all clients that attempts to intelligently chose a server based off how "busy" it already is in terms of CPU/Memory/Disk utilization, but that would be a herculean effort, and seems like we're trying to reinvent something that you would think someone would sell (although I haven't had any luck finding it). So in summary, are we missing an obvious solution for this, and does anyone know if any tools (for free or for purchase, doesn't matter) that facilitate running multiple SSIS ETL packages in parallel and on multiple servers? (What I would call a "queue & node based" system, but that's not an official term). Ultimately VMWare's Distributed Resource Scheduler addresses this as you simply run a consistent number of clients per VM that you know will never conflict scheduleing-wise, then leave it up to VMWare to move the VMs around to balance out hardware usage. I'm definitely not against using VMWare to do this, but since we're a 100% Microsoft app stack, it seems like -someone- out there would have solved this problem at the application layer instead of the hypervisor layer by checking on resource utilization at the OS, SQL, SSAS levels. I'm open to ANY discussion on this, and remember no suggestion is too crazy or radical! :-) Right now, VMWare is the only option we've found to get away from "manually" balancing our resources, so any suggestions that leave us on a pure Microsoft stack would be great. Thanks guys, Jeff

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• Configuration management in support of scientific computing

  - by Sharpie

  For the past few years I have been involved with developing and maintaining a system for forecasting near-shore waves. Our team has just received a significant grant for further development and as a result we are taking the opportunity to refactor many components of the old system. We will also be receiving a new server to run the model and so I am taking this opportunity to consider how we set up the system. Basically, the steps that need to happen are: Some standard packages and libraries such as compilers and databases need to be downloaded and installed. Some custom scientific models need to be downloaded and compiled from source as they are not commonly provided as packages. New users need to be created to manage the databases and run the models. A suite of scripts that manage model-database interaction needs to be checked out from source code control and installed. Crontabs need to be set up to run the scripts at regular intervals in order to generate forecasts. I have been pondering applying tools such as Puppet, Capistrano or Fabric to automate the above steps. It seems perfectly possible to implement most of the above functionality except there are a couple usage cases that I am wondering about: During my preliminary research, I have found few examples and little discussion on how to use these systems to abstract and automate the process of building custom components from source. We may have to deploy on machines that are isolated from the Internet- i.e. all configuration and set up files will have to come in on a USB key that can be inserted into a terminal that can connect to the server that will run the models. I see this as an opportunity to learn a new tool that will help me automate my workflow, but I am unsure which tool I should start with. If any member of the community could suggest a tool that would support the above workflow and the issues specific to scientific computing, I would be very grateful. Our production server will be running Linux, but support for OS X would be a bonus as it would allow the development team to setup test installations outside of VirtualBox.

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• Configuration management in support of scientific computing

  - by Sharpie

  For the past few years I have been involved with developing and maintaining a system for forecasting near-shore waves. Our team has just received a significant grant for further development and as a result we are taking the opportunity to refactor many components of the old system. We will also be receiving a new server to run the model and so I am taking this opportunity to consider how we set up the system. Basically, the steps that need to happen are: Some standard packages and libraries such as compilers and databases need to be downloaded and installed. Some custom scientific models need to be downloaded and compiled from source as they are not commonly provided as packages. New users need to be created to manage the databases and run the models. A suite of scripts that manage model-database interaction needs to be checked out from source code control and installed. Crontabs need to be set up to run the scripts at regular intervals in order to generate forecasts. I have been pondering applying tools such as Puppet, Capistrano or Fabric to automate the above steps. It seems perfectly possible to implement most of the above functionality except there are a couple usage cases that I am wondering about: During my preliminary research, I have found few examples and little discussion on how to use these systems to abstract and automate the process of building custom components from source. We may have to deploy on machines that are isolated from the Internet- i.e. all configuration and set up files will have to come in on a USB key that can be inserted into a terminal that can connect to the server that will run the models. I see this as an opportunity to learn a new tool that will help me automate my workflow, but I am unsure which tool I should start with. If any member of the community could suggest a tool that would support the above workflow and the issues specific to scientific computing, I would be very grateful. Our production server will be running Linux, but support for OS X would be a bonus as it would allow the development team to setup test installations outside of VirtualBox.

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• There's no sound on Ubuntu with an Intel HDA onboard chip and Realtek ALC1200 codec.

  - by Hanno Fietz

  For a while now, my sound has not been working in Ubuntu. It used to play OK, but after some upgrade (might have been distro upgrade to 9.10), it stopped working. I'm currently running 10.04 on an amd64 architecture. I'm using the builtin audio on a Foxconn motherboard, it's an ATI / Intel HDA chip with an Azalia controller, apparently it's using the Realtek ALC1200 codec. All the gory details here. I found a nice sound troubleshooting tutorial here, which is well-written and pretty extensive, however, I fail to look up the supported "models" for my soundcard. The troubleshooting page says to look for a section giving the codec used by your soundcard, which looks like this for me: !!HDA-Intel Codec information !!--------------------------- --startcollapse-- Codec: Realtek ALC1200 Then, I'm supposed to lookup the models for that codec in the file Documentation/ALSA-Configuration.txt in the appropriate directory of ALSA's git repository. Mine actually pointed me to a separate file, Documentation/HD-Audio-Models.txt, which, for my driver version is located here and contains no section related to ALC1200 codecs. I tried putting the driver options probe-mask=1 and model=auto in a config file for modprobe, as suggested elsewhere, but this just lead to snd-hda-intel not able to load at all anymore. I also tried installing the linux-backports-modules-alsa package for my kernel, because the description sounded promising, but that didn't change anything, either.

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• Windows Azure: Backup Services Release, Hyper-V Recovery Manager, VM Enhancements, Enhanced Enterprise Management Support

  - by ScottGu

  This morning we released a huge set of updates to Windows Azure.  These new capabilities include: Backup Services: General Availability of Windows Azure Backup Services Hyper-V Recovery Manager: Public preview of Windows Azure Hyper-V Recovery Manager Virtual Machines: Delete Attached Disks, Availability Set Warnings, SQL AlwaysOn Configuration Active Directory: Securely manage hundreds of SaaS applications Enterprise Management: Use Active Directory to Better Manage Windows Azure Windows Azure SDK 2.2: A massive update of our SDK + Visual Studio tooling support All of these improvements are now available to use immediately.  Below are more details about them. Backup Service: General Availability Release of Windows Azure Backup Today we are releasing Windows Azure Backup Service as a general availability service.  This release is now live in production, backed by an enterprise SLA, supported by Microsoft Support, and is ready to use for production scenarios. Windows Azure Backup is a cloud based backup solution for Windows Server which allows files and folders to be backed up and recovered from the cloud, and provides off-site protection against data loss. The service provides IT administrators and developers with the option to back up and protect critical data in an easily recoverable way from any location with no upfront hardware cost. Windows Azure Backup is built on the Windows Azure platform and uses Windows Azure blob storage for storing customer data. Windows Server uses the downloadable Windows Azure Backup Agent to transfer file and folder data securely and efficiently to the Windows Azure Backup Service. Along with providing cloud backup for Windows Server, Windows Azure Backup Service also provides capability to backup data from System Center Data Protection Manager and Windows Server Essentials, to the cloud. All data is encrypted onsite before it is sent to the cloud, and customers retain and manage the encryption key (meaning the data is stored entirely secured and can’t be decrypted by anyone but yourself). Getting Started To get started with the Windows Azure Backup Service, create a new Backup Vault within the Windows Azure Management Portal.  Click New->Data Services->Recovery Services->Backup Vault to do this: Once the backup vault is created you’ll be presented with a simple tutorial that will help guide you on how to register your Windows Servers with it: Once the servers you want to backup are registered, you can use the appropriate local management interface (such as the Microsoft Management Console snap-in, System Center Data Protection Manager Console, or Windows Server Essentials Dashboard) to configure the scheduled backups and to optionally initiate recoveries. You can follow these tutorials to learn more about how to do this: Tutorial: Schedule Backups Using the Windows Azure Backup Agent This tutorial helps you with setting up a backup schedule for your registered Windows Servers. Additionally, it also explains how to use Windows PowerShell cmdlets to set up a custom backup schedule. Tutorial: Recover Files and Folders Using the Windows Azure Backup Agent This tutorial helps you with recovering data from a backup. Additionally, it also explains how to use Windows PowerShell cmdlets to do the same tasks. Below are some of the key benefits the Windows Azure Backup Service provides: Simple configuration and management. Windows Azure Backup Service integrates with the familiar Windows Server Backup utility in Windows Server, the Data Protection Manager component in System Center and Windows Server Essentials, in order to provide a seamless backup and recovery experience to a local disk, or to the cloud. Block level incremental backups. The Windows Azure Backup Agent performs incremental backups by tracking file and block level changes and only transferring the changed blocks, hence reducing the storage and bandwidth utilization. Different point-in-time versions of the backups use storage efficiently by only storing the changes blocks between these versions. Data compression, encryption and throttling. The Windows Azure Backup Agent ensures that data is compressed and encrypted on the server before being sent to the Windows Azure Backup Service over the network. As a result, the Windows Azure Backup Service only stores encrypted data in the cloud storage. The encryption key is not available to the Windows Azure Backup Service, and as a result the data is never decrypted in the service. Also, users can setup throttling and configure how the Windows Azure Backup service utilizes the network bandwidth when backing up or restoring information. Data integrity is verified in the cloud. In addition to the secure backups, the backed up data is also automatically checked for integrity once the backup is done. As a result, any corruptions which may arise due to data transfer can be easily identified and are fixed automatically. Configurable retention policies for storing data in the cloud. The Windows Azure Backup Service accepts and implements retention policies to recycle backups that exceed the desired retention range, thereby meeting business policies and managing backup costs. Hyper-V Recovery Manager: Now Available in Public Preview I’m excited to also announce the public preview of a new Windows Azure Service – the Windows Azure Hyper-V Recovery Manager (HRM). Windows Azure Hyper-V Recovery Manager helps protect your business critical services by coordinating the replication and recovery of System Center Virtual Machine Manager 2012 SP1 and System Center Virtual Machine Manager 2012 R2 private clouds at a secondary location. With automated protection, asynchronous ongoing replication, and orderly recovery, the Hyper-V Recovery Manager service can help you implement Disaster Recovery and restore important services accurately, consistently, and with minimal downtime. Application data in an Hyper-V Recovery Manager scenarios always travels on your on-premise replication channel. Only metadata (such as names of logical clouds, virtual machines, networks etc.) that is needed for orchestration is sent to Azure. All traffic sent to/from Azure is encrypted. You can begin using Windows Azure Hyper-V Recovery today by clicking New->Data Services->Recovery Services->Hyper-V Recovery Manager within the Windows Azure Management Portal.  You can read more about Windows Azure Hyper-V Recovery Manager in Brad Anderson’s 9-part series, Transform the datacenter. To learn more about setting up Hyper-V Recovery Manager follow our detailed step-by-step guide. Virtual Machines: Delete Attached Disks, Availability Set Warnings, SQL AlwaysOn Today’s Windows Azure release includes a number of nice updates to Windows Azure Virtual Machines.  These improvements include: Ability to Delete both VM Instances + Attached Disks in One Operation Prior to today’s release, when you deleted VMs within Windows Azure we would delete the VM instance – but not delete the drives attached to the VM.  You had to manually delete these yourself from the storage account.  With today’s update we’ve added a convenience option that now allows you to either retain or delete the attached disks when you delete the VM:   We’ve also added the ability to delete a cloud service, its deployments, and its role instances with a single action. This can either be a cloud service that has production and staging deployments with web and worker roles, or a cloud service that contains virtual machines.  To do this, simply select the Cloud Service within the Windows Azure Management Portal and click the “Delete” button: Warnings on Availability Sets with Only One Virtual Machine In Them One of the nice features that Windows Azure Virtual Machines supports is the concept of “Availability Sets”.  An “availability set” allows you to define a tier/role (e.g. webfrontends, databaseservers, etc) that you can map Virtual Machines into – and when you do this Windows Azure separates them across fault domains and ensures that at least one of them is always available during servicing operations.  This enables you to deploy applications in a high availability way. One issue we’ve seen some customers run into is where they define an availability set, but then forget to map more than one VM into it (which defeats the purpose of having an availability set).  With today’s release we now display a warning in the Windows Azure Management Portal if you have only one virtual machine deployed in an availability set to help highlight this: You can learn more about configuring the availability of your virtual machines here. Configuring SQL Server Always On SQL Server Always On is a great feature that you can use with Windows Azure to enable high availability and DR scenarios with SQL Server. Today’s Windows Azure release makes it even easier to configure SQL Server Always On by enabling “Direct Server Return” endpoints to be configured and managed within the Windows Azure Management Portal.  Previously, setting this up required using PowerShell to complete the endpoint configuration.  Starting today you can enable this simply by checking the “Direct Server Return” checkbox: You can learn more about how to use direct server return for SQL Server AlwaysOn availability groups here. Active Directory: Application Access Enhancements This summer we released our initial preview of our Application Access Enhancements for Windows Azure Active Directory.  This service enables you to securely implement single-sign-on (SSO) support against SaaS applications (including Office 365, SalesForce, Workday, Box, Google Apps, GitHub, etc) as well as LOB based applications (including ones built with the new Windows Azure AD support we shipped last week with ASP.NET and VS 2013). Since the initial preview we’ve enhanced our SAML federation capabilities, integrated our new password vaulting system, and shipped multi-factor authentication support. We've also turned on our outbound identity provisioning system and have it working with hundreds of additional SaaS Applications: Earlier this month we published an update on dates and pricing for when the service will be released in general availability form.  In this blog post we announced our intention to release the service in general availability form by the end of the year.  We also announced that the below features would be available in a free tier with it: SSO to every SaaS app we integrate with – Users can Single Sign On to any app we are integrated with at no charge. This includes all the top SAAS Apps and every app in our application gallery whether they use federation or password vaulting. Application access assignment and removal – IT Admins can assign access privileges to web applications to the users in their active directory assuring that every employee has access to the SAAS Apps they need. And when a user leaves the company or changes jobs, the admin can just as easily remove their access privileges assuring data security and minimizing IP loss User provisioning (and de-provisioning) – IT admins will be able to automatically provision users in 3rd party SaaS applications like Box, Salesforce.com, GoToMeeting, DropBox and others. We are working with key partners in the ecosystem to establish these connections, meaning you no longer have to continually update user records in multiple systems. Security and auditing reports – Security is a key priority for us. With the free version of these enhancements you'll get access to our standard set of access reports giving you visibility into which users are using which applications, when they were using them and where they are using them from. In addition, we'll alert you to un-usual usage patterns for instance when a user logs in from multiple locations at the same time. Our Application Access Panel – Users are logging in from every type of devices including Windows, iOS, & Android. Not all of these devices handle authentication in the same manner but the user doesn't care. They need to access their apps from the devices they love. Our Application Access Panel will support the ability for users to access access and launch their apps from any device and anywhere. You can learn more about our plans for application management with Windows Azure Active Directory here.  Try out the preview and start using it today. Enterprise Management: Use Active Directory to Better Manage Windows Azure Windows Azure Active Directory provides the ability to manage your organization in a directory which is hosted entirely in the cloud, or alternatively kept in sync with an on-premises Windows Server Active Directory solution (allowing you to seamlessly integrate with the directory you already have).  With today’s Windows Azure release we are integrating Windows Azure Active Directory even more within the core Windows Azure management experience, and enabling an even richer enterprise security offering.  Specifically: 1) All Windows Azure accounts now have a default Windows Azure Active Directory created for them.  You can create and map any users you want into this directory, and grant administrative rights to manage resources in Windows Azure to these users. 2) You can keep this directory entirely hosted in the cloud – or optionally sync it with your on-premises Windows Server Active Directory.  Both options are free.  The later approach is ideal for companies that wish to use their corporate user identities to sign-in and manage Windows Azure resources.  It also ensures that if an employee leaves an organization, his or her access control rights to the company’s Windows Azure resources are immediately revoked. 3) The Windows Azure Service Management APIs have been updated to support using Windows Azure Active Directory credentials to sign-in and perform management operations.  Prior to today’s release customers had to download and use management certificates (which were not scoped to individual users) to perform management operations.  We still support this management certificate approach (don’t worry – nothing will stop working).  But we think the new Windows Azure Active Directory authentication support enables an even easier and more secure way for customers to manage resources going forward.  4) The Windows Azure SDK 2.2 release (which is also shipping today) includes built-in support for the new Service Management APIs that authenticate with Windows Azure Active Directory, and now allow you to create and manage Windows Azure applications and resources directly within Visual Studio using your Active Directory credentials.  This, combined with updated PowerShell scripts that also support Active Directory, enables an end-to-end enterprise authentication story with Windows Azure. Below are some details on how all of this works: Subscriptions within a Directory As part of today’s update, we have associated all existing Window Azure accounts with a Windows Azure Active Directory (and created one for you if you don’t already have one). When you login to the Windows Azure Management Portal you’ll now see the directory name in the URI of the browser.  For example, in the screen-shot below you can see that I have a “scottgu” directory that my subscriptions are hosted within: Note that you can continue to use Microsoft Accounts (formerly known as Microsoft Live IDs) to sign-into Windows Azure.  These map just fine to a Windows Azure Active Directory – so there is no need to create new usernames that are specific to a directory if you don’t want to.  In the scenario above I’m actually logged in using my @hotmail.com based Microsoft ID which is now mapped to a “scottgu” active directory that was created for me.  By default everything will continue to work just like you used to before. Manage your Directory You can manage an Active Directory (including the one we now create for you by default) by clicking the “Active Directory” tab in the left-hand side of the portal.  This will list all of the directories in your account.  Clicking one the first time will display a getting started page that provides documentation and links to perform common tasks with it: You can use the built-in directory management support within the Windows Azure Management Portal to add/remove/manage users within the directory, enable multi-factor authentication, associate a custom domain (e.g. mycompanyname.com) with the directory, and/or rename the directory to whatever friendly name you want (just click the configure tab to do this).  You can also setup the directory to automatically sync with an on-premises Active Directory using the “Directory Integration” tab. Note that users within a directory by default do not have admin rights to login or manage Windows Azure based resources.  You still need to explicitly grant them co-admin permissions on a subscription for them to login or manage resources in Windows Azure.  You can do this by clicking the Settings tab on the left-hand side of the portal and then by clicking the administrators tab within it. Sign-In Integration within Visual Studio If you install the new Windows Azure SDK 2.2 release, you can now connect to Windows Azure from directly inside Visual Studio without having to download any management certificates.  You can now just right-click on the “Windows Azure” icon within the Server Explorer and choose the “Connect to Windows Azure” context menu option to do so: Doing this will prompt you to enter the email address of the username you wish to sign-in with (make sure this account is a user in your directory with co-admin rights on a subscription): You can use either a Microsoft Account (e.g. Windows Live ID) or an Active Directory based Organizational account as the email.  The dialog will update with an appropriate login prompt depending on which type of email address you enter: Once you sign-in you’ll see the Windows Azure resources that you have permissions to manage show up automatically within the Visual Studio server explorer and be available to start using: No downloading of management certificates required.  All of the authentication was handled using your Windows Azure Active Directory! Manage Subscriptions across Multiple Directories If you have already have multiple directories and multiple subscriptions within your Windows Azure account, we have done our best to create a good default mapping of your subscriptions->directories as part of today’s update.  If you don’t like the default subscription-to-directory mapping we have done you can click the Settings tab in the left-hand navigation of the Windows Azure Management Portal and browse to the Subscriptions tab within it: If you want to map a subscription under a different directory in your account, simply select the subscription from the list, and then click the “Edit Directory” button to choose which directory to map it to.  Mapping a subscription to a different directory takes only seconds and will not cause any of the resources within the subscription to recycle or stop working.  We’ve made the directory->subscription mapping process self-service so that you always have complete control and can map things however you want. Filtering By Directory and Subscription Within the Windows Azure Management Portal you can filter resources in the portal by subscription (allowing you to show/hide different subscriptions).  If you have subscriptions mapped to multiple directory tenants, we also now have a filter drop-down that allows you to filter the subscription list by directory tenant.  This filter is only available if you have multiple subscriptions mapped to multiple directories within your Windows Azure Account:   Windows Azure SDK 2.2 Today we are also releasing a major update of our Windows Azure SDK.  The Windows Azure SDK 2.2 release adds some great new features including: Visual Studio 2013 Support Integrated Windows Azure Sign-In support within Visual Studio Remote Debugging Cloud Services with Visual Studio Firewall Management support within Visual Studio for SQL Databases Visual Studio 2013 RTM VM Images for MSDN Subscribers Windows Azure Management Libraries for .NET Updated Windows Azure PowerShell Cmdlets and ScriptCenter I’ll post a follow-up blog shortly with more details about all of the above. Additional Updates In addition to the above enhancements, today’s release also includes a number of additional improvements: AutoScale: Richer time and date based scheduling support (set different rules on different dates) AutoScale: Ability to Scale to Zero Virtual Machines (very useful for Dev/Test scenarios) AutoScale: Support for time-based scheduling of Mobile Service AutoScale rules Operation Logs: Auditing support for Service Bus management operations Today we also shipped a major update to the Windows Azure SDK – Windows Azure SDK 2.2.  It has so much goodness in it that I have a whole second blog post coming shortly on it! :-) Summary Today’s Windows Azure release enables a bunch of great new scenarios, and enables a much richer enterprise authentication offering. If you don’t already have a Windows Azure account, you can sign-up for a free trial and start using all of the above features today.  Then visit the Windows Azure Developer Center to learn more about how to build apps with it. Hope this helps, Scott P.S. In addition to blogging, I am also now using Twitter for quick updates and to share links. Follow me at: twitter.com/scottgu

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• C#/.NET Little Wonders: The Concurrent Collections (1 of 3)

  - by James Michael Hare

  Once again we consider some of the lesser known classes and keywords of C#.  In the next few weeks, we will discuss the concurrent collections and how they have changed the face of concurrent programming. This week’s post will begin with a general introduction and discuss the ConcurrentStack<T> and ConcurrentQueue<T>.  Then in the following post we’ll discuss the ConcurrentDictionary<T> and ConcurrentBag<T>.  Finally, we shall close on the third post with a discussion of the BlockingCollection<T>. For more of the "Little Wonders" posts, see the index here. A brief history of collections In the beginning was the .NET 1.0 Framework.  And out of this framework emerged the System.Collections namespace, and it was good.  It contained all the basic things a growing programming language needs like the ArrayList and Hashtable collections.  The main problem, of course, with these original collections is that they held items of type object which means you had to be disciplined enough to use them correctly or you could end up with runtime errors if you got an object of a type you weren't expecting. Then came .NET 2.0 and generics and our world changed forever!  With generics the C# language finally got an equivalent of the very powerful C++ templates.  As such, the System.Collections.Generic was born and we got type-safe versions of all are favorite collections.  The List<T> succeeded the ArrayList and the Dictionary<TKey,TValue> succeeded the Hashtable and so on.  The new versions of the library were not only safer because they checked types at compile-time, in many cases they were more performant as well.  So much so that it's Microsoft's recommendation that the System.Collections original collections only be used for backwards compatibility. So we as developers came to know and love the generic collections and took them into our hearts and embraced them.  The problem is, thread safety in both the original collections and the generic collections can be problematic, for very different reasons. Now, if you are only doing single-threaded development you may not care – after all, no locking is required.  Even if you do have multiple threads, if a collection is “load-once, read-many” you don’t need to do anything to protect that container from multi-threaded access, as illustrated below: 1: public static class OrderTypeTranslator 2: { 3: // because this dictionary is loaded once before it is ever accessed, we don't need to synchronize 4: // multi-threaded read access 5: private static readonly Dictionary<string, char> _translator = new Dictionary<string, char> 6: { 7: {"New", 'N'}, 8: {"Update", 'U'}, 9: {"Cancel", 'X'} 10: }; 11:  12: // the only public interface into the dictionary is for reading, so inherently thread-safe 13: public static char? Translate(string orderType) 14: { 15: char charValue; 16: if (_translator.TryGetValue(orderType, out charValue)) 17: { 18: return charValue; 19: } 20:  21: return null; 22: } 23: } Unfortunately, most of our computer science problems cannot get by with just single-threaded applications or with multi-threading in a load-once manner.  Looking at  today's trends, it's clear to see that computers are not so much getting faster because of faster processor speeds -- we've nearly reached the limits we can push through with today's technologies -- but more because we're adding more cores to the boxes.  With this new hardware paradigm, it is even more important to use multi-threaded applications to take full advantage of parallel processing to achieve higher application speeds. So let's look at how to use collections in a thread-safe manner. Using historical collections in a concurrent fashion The early .NET collections (System.Collections) had a Synchronized() static method that could be used to wrap the early collections to make them completely thread-safe.  This paradigm was dropped in the generic collections (System.Collections.Generic) because having a synchronized wrapper resulted in atomic locks for all operations, which could prove overkill in many multithreading situations.  Thus the paradigm shifted to having the user of the collection specify their own locking, usually with an external object: 1: public class OrderAggregator 2: { 3: private static readonly Dictionary<string, List<Order>> _orders = new Dictionary<string, List<Order>>(); 4: private static readonly _orderLock = new object(); 5:  6: public void Add(string accountNumber, Order newOrder) 7: { 8: List<Order> ordersForAccount; 9:  10: // a complex operation like this should all be protected 11: lock (_orderLock) 12: { 13: if (!_orders.TryGetValue(accountNumber, out ordersForAccount)) 14: { 15: _orders.Add(accountNumber, ordersForAccount = new List<Order>()); 16: } 17:  18: ordersForAccount.Add(newOrder); 19: } 20: } 21: } Notice how we’re performing several operations on the dictionary under one lock.  With the Synchronized() static methods of the early collections, you wouldn’t be able to specify this level of locking (a more macro-level).  So in the generic collections, it was decided that if a user needed synchronization, they could implement their own locking scheme instead so that they could provide synchronization as needed. The need for better concurrent access to collections Here’s the problem: it’s relatively easy to write a collection that locks itself down completely for access, but anything more complex than that can be difficult and error-prone to write, and much less to make it perform efficiently!  For example, what if you have a Dictionary that has frequent reads but in-frequent updates?  Do you want to lock down the entire Dictionary for every access?  This would be overkill and would prevent concurrent reads.  In such cases you could use something like a ReaderWriterLockSlim which allows for multiple readers in a lock, and then once a writer grabs the lock it blocks all further readers until the writer is done (in a nutshell).  This is all very complex stuff to consider. Fortunately, this is where the Concurrent Collections come in.  The Parallel Computing Platform team at Microsoft went through great pains to determine how to make a set of concurrent collections that would have the best performance characteristics for general case multi-threaded use. Now, as in all things involving threading, you should always make sure you evaluate all your container options based on the particular usage scenario and the degree of parallelism you wish to acheive. This article should not be taken to understand that these collections are always supperior to the generic collections. Each fills a particular need for a particular situation. Understanding what each container is optimized for is key to the success of your application whether it be single-threaded or multi-threaded. General points to consider with the concurrent collections The MSDN points out that the concurrent collections all support the ICollection interface. However, since the collections are already synchronized, the IsSynchronized property always returns false, and SyncRoot always returns null.  Thus you should not attempt to use these properties for synchronization purposes. Note that since the concurrent collections also may have different operations than the traditional data structures you may be used to.  Now you may ask why they did this, but it was done out of necessity to keep operations safe and atomic.  For example, in order to do a Pop() on a stack you have to know the stack is non-empty, but between the time you check the stack’s IsEmpty property and then do the Pop() another thread may have come in and made the stack empty!  This is why some of the traditional operations have been changed to make them safe for concurrent use. In addition, some properties and methods in the concurrent collections achieve concurrency by creating a snapshot of the collection, which means that some operations that were traditionally O(1) may now be O(n) in the concurrent models.  I’ll try to point these out as we talk about each collection so you can be aware of any potential performance impacts.  Finally, all the concurrent containers are safe for enumeration even while being modified, but some of the containers support this in different ways (snapshot vs. dirty iteration).  Once again I’ll highlight how thread-safe enumeration works for each collection. ConcurrentStack<T>: The thread-safe LIFO container The ConcurrentStack<T> is the thread-safe counterpart to the System.Collections.Generic.Stack<T>, which as you may remember is your standard last-in-first-out container.  If you think of algorithms that favor stack usage (for example, depth-first searches of graphs and trees) then you can see how using a thread-safe stack would be of benefit. The ConcurrentStack<T> achieves thread-safe access by using System.Threading.Interlocked operations.  This means that the multi-threaded access to the stack requires no traditional locking and is very, very fast! For the most part, the ConcurrentStack<T> behaves like it’s Stack<T> counterpart with a few differences: Pop() was removed in favor of TryPop() Returns true if an item existed and was popped and false if empty. PushRange() and TryPopRange() were added Allows you to push multiple items and pop multiple items atomically. Count takes a snapshot of the stack and then counts the items. This means it is a O(n) operation, if you just want to check for an empty stack, call IsEmpty instead which is O(1). ToArray() and GetEnumerator() both also take snapshots. This means that iteration over a stack will give you a static view at the time of the call and will not reflect updates. Pushing on a ConcurrentStack<T> works just like you’d expect except for the aforementioned PushRange() method that was added to allow you to push a range of items concurrently. 1: var stack = new ConcurrentStack<string>(); 2:  3: // adding to stack is much the same as before 4: stack.Push("First"); 5:  6: // but you can also push multiple items in one atomic operation (no interleaves) 7: stack.PushRange(new [] { "Second", "Third", "Fourth" }); For looking at the top item of the stack (without removing it) the Peek() method has been removed in favor of a TryPeek().  This is because in order to do a peek the stack must be non-empty, but between the time you check for empty and the time you execute the peek the stack contents may have changed.  Thus the TryPeek() was created to be an atomic check for empty, and then peek if not empty: 1: // to look at top item of stack without removing it, can use TryPeek. 2: // Note that there is no Peek(), this is because you need to check for empty first. TryPeek does. 3: string item; 4: if (stack.TryPeek(out item)) 5: { 6: Console.WriteLine("Top item was " + item); 7: } 8: else 9: { 10: Console.WriteLine("Stack was empty."); 11: } Finally, to remove items from the stack, we have the TryPop() for single, and TryPopRange() for multiple items.  Just like the TryPeek(), these operations replace Pop() since we need to ensure atomically that the stack is non-empty before we pop from it: 1: // to remove items, use TryPop or TryPopRange to get multiple items atomically (no interleaves) 2: if (stack.TryPop(out item)) 3: { 4: Console.WriteLine("Popped " + item); 5: } 6:  7: // TryPopRange will only pop up to the number of spaces in the array, the actual number popped is returned. 8: var poppedItems = new string[2]; 9: int numPopped = stack.TryPopRange(poppedItems); 10:  11: foreach (var theItem in poppedItems.Take(numPopped)) 12: { 13: Console.WriteLine("Popped " + theItem); 14: } Finally, note that as stated before, GetEnumerator() and ToArray() gets a snapshot of the data at the time of the call.  That means if you are enumerating the stack you will get a snapshot of the stack at the time of the call.  This is illustrated below: 1: var stack = new ConcurrentStack<string>(); 2:  3: // adding to stack is much the same as before 4: stack.Push("First"); 5:  6: var results = stack.GetEnumerator(); 7:  8: // but you can also push multiple items in one atomic operation (no interleaves) 9: stack.PushRange(new [] { "Second", "Third", "Fourth" }); 10:  11: while(results.MoveNext()) 12: { 13: Console.WriteLine("Stack only has: " + results.Current); 14: } The only item that will be printed out in the above code is "First" because the snapshot was taken before the other items were added. This may sound like an issue, but it’s really for safety and is more correct.  You don’t want to enumerate a stack and have half a view of the stack before an update and half a view of the stack after an update, after all.  In addition, note that this is still thread-safe, whereas iterating through a non-concurrent collection while updating it in the old collections would cause an exception. ConcurrentQueue<T>: The thread-safe FIFO container The ConcurrentQueue<T> is the thread-safe counterpart of the System.Collections.Generic.Queue<T> class.  The concurrent queue uses an underlying list of small arrays and lock-free System.Threading.Interlocked operations on the head and tail arrays.  Once again, this allows us to do thread-safe operations without the need for heavy locks! The ConcurrentQueue<T> (like the ConcurrentStack<T>) has some departures from the non-concurrent counterpart.  Most notably: Dequeue() was removed in favor of TryDequeue(). Returns true if an item existed and was dequeued and false if empty. Count does not take a snapshot It subtracts the head and tail index to get the count.  This results overall in a O(1) complexity which is quite good.  It’s still recommended, however, that for empty checks you call IsEmpty instead of comparing Count to zero. ToArray() and GetEnumerator() both take snapshots. This means that iteration over a queue will give you a static view at the time of the call and will not reflect updates. The Enqueue() method on the ConcurrentQueue<T> works much the same as the generic Queue<T>: 1: var queue = new ConcurrentQueue<string>(); 2:  3: // adding to queue is much the same as before 4: queue.Enqueue("First"); 5: queue.Enqueue("Second"); 6: queue.Enqueue("Third"); For front item access, the TryPeek() method must be used to attempt to see the first item if the queue.  There is no Peek() method since, as you’ll remember, we can only peek on a non-empty queue, so we must have an atomic TryPeek() that checks for empty and then returns the first item if the queue is non-empty. 1: // to look at first item in queue without removing it, can use TryPeek. 2: // Note that there is no Peek(), this is because you need to check for empty first. TryPeek does. 3: string item; 4: if (queue.TryPeek(out item)) 5: { 6: Console.WriteLine("First item was " + item); 7: } 8: else 9: { 10: Console.WriteLine("Queue was empty."); 11: } Then, to remove items you use TryDequeue().  Once again this is for the same reason we have TryPeek() and not Peek(): 1: // to remove items, use TryDequeue. If queue is empty returns false. 2: if (queue.TryDequeue(out item)) 3: { 4: Console.WriteLine("Dequeued first item " + item); 5: } Just like the concurrent stack, the ConcurrentQueue<T> takes a snapshot when you call ToArray() or GetEnumerator() which means that subsequent updates to the queue will not be seen when you iterate over the results.  Thus once again the code below will only show the first item, since the other items were added after the snapshot. 1: var queue = new ConcurrentQueue<string>(); 2:  3: // adding to queue is much the same as before 4: queue.Enqueue("First"); 5:  6: var iterator = queue.GetEnumerator(); 7:  8: queue.Enqueue("Second"); 9: queue.Enqueue("Third"); 10:  11: // only shows First 12: while (iterator.MoveNext()) 13: { 14: Console.WriteLine("Dequeued item " + iterator.Current); 15: } Using collections concurrently You’ll notice in the examples above I stuck to using single-threaded examples so as to make them deterministic and the results obvious.  Of course, if we used these collections in a truly multi-threaded way the results would be less deterministic, but would still be thread-safe and with no locking on your part required! For example, say you have an order processor that takes an IEnumerable<Order> and handles each other in a multi-threaded fashion, then groups the responses together in a concurrent collection for aggregation.  This can be done easily with the TPL’s Parallel.ForEach(): 1: public static IEnumerable<OrderResult> ProcessOrders(IEnumerable<Order> orderList) 2: { 3: var proxy = new OrderProxy(); 4: var results = new ConcurrentQueue<OrderResult>(); 5:  6: // notice that we can process all these in parallel and put the results 7: // into our concurrent collection without needing any external locking! 8: Parallel.ForEach(orderList, 9: order => 10: { 11: var result = proxy.PlaceOrder(order); 12:  13: results.Enqueue(result); 14: }); 15:  16: return results; 17: } Summary Obviously, if you do not need multi-threaded safety, you don’t need to use these collections, but when you do need multi-threaded collections these are just the ticket! The plethora of features (I always think of the movie The Three Amigos when I say plethora) built into these containers and the amazing way they acheive thread-safe access in an efficient manner is wonderful to behold. Stay tuned next week where we’ll continue our discussion with the ConcurrentBag<T> and the ConcurrentDictionary<TKey,TValue>. For some excellent information on the performance of the concurrent collections and how they perform compared to a traditional brute-force locking strategy, see this wonderful whitepaper by the Microsoft Parallel Computing Platform team here.   Tweet Technorati Tags: C#,.NET,Concurrent Collections,Collections,Multi-Threading,Little Wonders,BlackRabbitCoder,James Michael Hare

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  We have already covered the BYOD requirements that an application developer is faced with, in an earlier blog entry ( How to Bring Your Own Device (BYOD) to a .NET application ). In that entry we emphasized the fact that application developers will need to prepare their applications for serving multiple types of devices on multiple platforms, ranging from the smallest mobile devices up to and beyond the largest desktop devices. The experts prediction is that in the near future we will see that the...(read more)

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• Prevent virtual host on same server interact on apache [closed]

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