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  • Toorcon14

    - by danx
    Toorcon 2012 Information Security Conference San Diego, CA, http://www.toorcon.org/ Dan Anderson, October 2012 It's almost Halloween, and we all know what that means—yes, of course, it's time for another Toorcon Conference! Toorcon is an annual conference for people interested in computer security. This includes the whole range of hackers, computer hobbyists, professionals, security consultants, press, law enforcement, prosecutors, FBI, etc. We're at Toorcon 14—see earlier blogs for some of the previous Toorcon's I've attended (back to 2003). This year's "con" was held at the Westin on Broadway in downtown San Diego, California. The following are not necessarily my views—I'm just the messenger—although I could have misquoted or misparaphrased the speakers. Also, I only reviewed some of the talks, below, which I attended and interested me. MalAndroid—the Crux of Android Infections, Aditya K. Sood Programming Weird Machines with ELF Metadata, Rebecca "bx" Shapiro Privacy at the Handset: New FCC Rules?, Valkyrie Hacking Measured Boot and UEFI, Dan Griffin You Can't Buy Security: Building the Open Source InfoSec Program, Boris Sverdlik What Journalists Want: The Investigative Reporters' Perspective on Hacking, Dave Maas & Jason Leopold Accessibility and Security, Anna Shubina Stop Patching, for Stronger PCI Compliance, Adam Brand McAfee Secure & Trustmarks — a Hacker's Best Friend, Jay James & Shane MacDougall MalAndroid—the Crux of Android Infections Aditya K. Sood, IOActive, Michigan State PhD candidate Aditya talked about Android smartphone malware. There's a lot of old Android software out there—over 50% Gingerbread (2.3.x)—and most have unpatched vulnerabilities. Of 9 Android vulnerabilities, 8 have known exploits (such as the old Gingerbread Global Object Table exploit). Android protection includes sandboxing, security scanner, app permissions, and screened Android app market. The Android permission checker has fine-grain resource control, policy enforcement. Android static analysis also includes a static analysis app checker (bouncer), and a vulnerablity checker. What security problems does Android have? User-centric security, which depends on the user to grant permission and make smart decisions. But users don't care or think about malware (the're not aware, not paranoid). All they want is functionality, extensibility, mobility Android had no "proper" encryption before Android 3.0 No built-in protection against social engineering and web tricks Alternative Android app markets are unsafe. Simply visiting some markets can infect Android Aditya classified Android Malware types as: Type A—Apps. These interact with the Android app framework. For example, a fake Netflix app. Or Android Gold Dream (game), which uploads user files stealthy manner to a remote location. Type K—Kernel. Exploits underlying Linux libraries or kernel Type H—Hybrid. These use multiple layers (app framework, libraries, kernel). These are most commonly used by Android botnets, which are popular with Chinese botnet authors What are the threats from Android malware? These incude leak info (contacts), banking fraud, corporate network attacks, malware advertising, malware "Hackivism" (the promotion of social causes. For example, promiting specific leaders of the Tunisian or Iranian revolutions. Android malware is frequently "masquerated". That is, repackaged inside a legit app with malware. To avoid detection, the hidden malware is not unwrapped until runtime. The malware payload can be hidden in, for example, PNG files. Less common are Android bootkits—there's not many around. What they do is hijack the Android init framework—alteering system programs and daemons, then deletes itself. For example, the DKF Bootkit (China). Android App Problems: no code signing! all self-signed native code execution permission sandbox — all or none alternate market places no robust Android malware detection at network level delayed patch process Programming Weird Machines with ELF Metadata Rebecca "bx" Shapiro, Dartmouth College, NH https://github.com/bx/elf-bf-tools @bxsays on twitter Definitions. "ELF" is an executable file format used in linking and loading executables (on UNIX/Linux-class machines). "Weird machine" uses undocumented computation sources (I think of them as unintended virtual machines). Some examples of "weird machines" are those that: return to weird location, does SQL injection, corrupts the heap. Bx then talked about using ELF metadata as (an uintended) "weird machine". Some ELF background: A compiler takes source code and generates a ELF object file (hello.o). A static linker makes an ELF executable from the object file. A runtime linker and loader takes ELF executable and loads and relocates it in memory. The ELF file has symbols to relocate functions and variables. ELF has two relocation tables—one at link time and another one at loading time: .rela.dyn (link time) and .dynsym (dynamic table). GOT: Global Offset Table of addresses for dynamically-linked functions. PLT: Procedure Linkage Tables—works with GOT. The memory layout of a process (not the ELF file) is, in order: program (+ heap), dynamic libraries, libc, ld.so, stack (which includes the dynamic table loaded into memory) For ELF, the "weird machine" is found and exploited in the loader. ELF can be crafted for executing viruses, by tricking runtime into executing interpreted "code" in the ELF symbol table. One can inject parasitic "code" without modifying the actual ELF code portions. Think of the ELF symbol table as an "assembly language" interpreter. It has these elements: instructions: Add, move, jump if not 0 (jnz) Think of symbol table entries as "registers" symbol table value is "contents" immediate values are constants direct values are addresses (e.g., 0xdeadbeef) move instruction: is a relocation table entry add instruction: relocation table "addend" entry jnz instruction: takes multiple relocation table entries The ELF weird machine exploits the loader by relocating relocation table entries. The loader will go on forever until told to stop. It stores state on stack at "end" and uses IFUNC table entries (containing function pointer address). The ELF weird machine, called "Brainfu*k" (BF) has: 8 instructions: pointer inc, dec, inc indirect, dec indirect, jump forward, jump backward, print. Three registers - 3 registers Bx showed example BF source code that implemented a Turing machine printing "hello, world". More interesting was the next demo, where bx modified ping. Ping runs suid as root, but quickly drops privilege. BF modified the loader to disable the library function call dropping privilege, so it remained as root. Then BF modified the ping -t argument to execute the -t filename as root. It's best to show what this modified ping does with an example: $ whoami bx $ ping localhost -t backdoor.sh # executes backdoor $ whoami root $ The modified code increased from 285948 bytes to 290209 bytes. A BF tool compiles "executable" by modifying the symbol table in an existing ELF executable. The tool modifies .dynsym and .rela.dyn table, but not code or data. Privacy at the Handset: New FCC Rules? "Valkyrie" (Christie Dudley, Santa Clara Law JD candidate) Valkyrie talked about mobile handset privacy. Some background: Senator Franken (also a comedian) became alarmed about CarrierIQ, where the carriers track their customers. Franken asked the FCC to find out what obligations carriers think they have to protect privacy. The carriers' response was that they are doing just fine with self-regulation—no worries! Carriers need to collect data, such as missed calls, to maintain network quality. But carriers also sell data for marketing. Verizon sells customer data and enables this with a narrow privacy policy (only 1 month to opt out, with difficulties). The data sold is not individually identifiable and is aggregated. But Verizon recommends, as an aggregation workaround to "recollate" data to other databases to identify customers indirectly. The FCC has regulated telephone privacy since 1934 and mobile network privacy since 2007. Also, the carriers say mobile phone privacy is a FTC responsibility (not FCC). FTC is trying to improve mobile app privacy, but FTC has no authority over carrier / customer relationships. As a side note, Apple iPhones are unique as carriers have extra control over iPhones they don't have with other smartphones. As a result iPhones may be more regulated. Who are the consumer advocates? Everyone knows EFF, but EPIC (Electrnic Privacy Info Center), although more obsecure, is more relevant. What to do? Carriers must be accountable. Opt-in and opt-out at any time. Carriers need incentive to grant users control for those who want it, by holding them liable and responsible for breeches on their clock. Location information should be added current CPNI privacy protection, and require "Pen/trap" judicial order to obtain (and would still be a lower standard than 4th Amendment). Politics are on a pro-privacy swing now, with many senators and the Whitehouse. There will probably be new regulation soon, and enforcement will be a problem, but consumers will still have some benefit. Hacking Measured Boot and UEFI Dan Griffin, JWSecure, Inc., Seattle, @JWSdan Dan talked about hacking measured UEFI boot. First some terms: UEFI is a boot technology that is replacing BIOS (has whitelisting and blacklisting). UEFI protects devices against rootkits. TPM - hardware security device to store hashs and hardware-protected keys "secure boot" can control at firmware level what boot images can boot "measured boot" OS feature that tracks hashes (from BIOS, boot loader, krnel, early drivers). "remote attestation" allows remote validation and control based on policy on a remote attestation server. Microsoft pushing TPM (Windows 8 required), but Google is not. Intel TianoCore is the only open source for UEFI. Dan has Measured Boot Tool at http://mbt.codeplex.com/ with a demo where you can also view TPM data. TPM support already on enterprise-class machines. UEFI Weaknesses. UEFI toolkits are evolving rapidly, but UEFI has weaknesses: assume user is an ally trust TPM implicitly, and attached to computer hibernate file is unprotected (disk encryption protects against this) protection migrating from hardware to firmware delays in patching and whitelist updates will UEFI really be adopted by the mainstream (smartphone hardware support, bank support, apathetic consumer support) You Can't Buy Security: Building the Open Source InfoSec Program Boris Sverdlik, ISDPodcast.com co-host Boris talked about problems typical with current security audits. "IT Security" is an oxymoron—IT exists to enable buiness, uptime, utilization, reporting, but don't care about security—IT has conflict of interest. There's no Magic Bullet ("blinky box"), no one-size-fits-all solution (e.g., Intrusion Detection Systems (IDSs)). Regulations don't make you secure. The cloud is not secure (because of shared data and admin access). Defense and pen testing is not sexy. Auditors are not solution (security not a checklist)—what's needed is experience and adaptability—need soft skills. Step 1: First thing is to Google and learn the company end-to-end before you start. Get to know the management team (not IT team), meet as many people as you can. Don't use arbitrary values such as CISSP scores. Quantitive risk assessment is a myth (e.g. AV*EF-SLE). Learn different Business Units, legal/regulatory obligations, learn the business and where the money is made, verify company is protected from script kiddies (easy), learn sensitive information (IP, internal use only), and start with low-hanging fruit (customer service reps and social engineering). Step 2: Policies. Keep policies short and relevant. Generic SANS "security" boilerplate policies don't make sense and are not followed. Focus on acceptable use, data usage, communications, physical security. Step 3: Implementation: keep it simple stupid. Open source, although useful, is not free (implementation cost). Access controls with authentication & authorization for local and remote access. MS Windows has it, otherwise use OpenLDAP, OpenIAM, etc. Application security Everyone tries to reinvent the wheel—use existing static analysis tools. Review high-risk apps and major revisions. Don't run different risk level apps on same system. Assume host/client compromised and use app-level security control. Network security VLAN != segregated because there's too many workarounds. Use explicit firwall rules, active and passive network monitoring (snort is free), disallow end user access to production environment, have a proxy instead of direct Internet access. Also, SSL certificates are not good two-factor auth and SSL does not mean "safe." Operational Controls Have change, patch, asset, & vulnerability management (OSSI is free). For change management, always review code before pushing to production For logging, have centralized security logging for business-critical systems, separate security logging from administrative/IT logging, and lock down log (as it has everything). Monitor with OSSIM (open source). Use intrusion detection, but not just to fulfill a checkbox: build rules from a whitelist perspective (snort). OSSEC has 95% of what you need. Vulnerability management is a QA function when done right: OpenVas and Seccubus are free. Security awareness The reality is users will always click everything. Build real awareness, not compliance driven checkbox, and have it integrated into the culture. Pen test by crowd sourcing—test with logging COSSP http://www.cossp.org/ - Comprehensive Open Source Security Project What Journalists Want: The Investigative Reporters' Perspective on Hacking Dave Maas, San Diego CityBeat Jason Leopold, Truthout.org The difference between hackers and investigative journalists: For hackers, the motivation varies, but method is same, technological specialties. For investigative journalists, it's about one thing—The Story, and they need broad info-gathering skills. J-School in 60 Seconds: Generic formula: Person or issue of pubic interest, new info, or angle. Generic criteria: proximity, prominence, timeliness, human interest, oddity, or consequence. Media awareness of hackers and trends: journalists becoming extremely aware of hackers with congressional debates (privacy, data breaches), demand for data-mining Journalists, use of coding and web development for Journalists, and Journalists busted for hacking (Murdock). Info gathering by investigative journalists include Public records laws. Federal Freedom of Information Act (FOIA) is good, but slow. California Public Records Act is a lot stronger. FOIA takes forever because of foot-dragging—it helps to be specific. Often need to sue (especially FBI). CPRA is faster, and requests can be vague. Dumps and leaks (a la Wikileaks) Journalists want: leads, protecting ourselves, our sources, and adapting tools for news gathering (Google hacking). Anonomity is important to whistleblowers. They want no digital footprint left behind (e.g., email, web log). They don't trust encryption, want to feel safe and secure. Whistleblower laws are very weak—there's no upside for whistleblowers—they have to be very passionate to do it. Accessibility and Security or: How I Learned to Stop Worrying and Love the Halting Problem Anna Shubina, Dartmouth College Anna talked about how accessibility and security are related. Accessibility of digital content (not real world accessibility). mostly refers to blind users and screenreaders, for our purpose. Accessibility is about parsing documents, as are many security issues. "Rich" executable content causes accessibility to fail, and often causes security to fail. For example MS Word has executable format—it's not a document exchange format—more dangerous than PDF or HTML. Accessibility is often the first and maybe only sanity check with parsing. They have no choice because someone may want to read what you write. Google, for example, is very particular about web browser you use and are bad at supporting other browsers. Uses JavaScript instead of links, often requiring mouseover to display content. PDF is a security nightmare. Executible format, embedded flash, JavaScript, etc. 15 million lines of code. Google Chrome doesn't handle PDF correctly, causing several security bugs. PDF has an accessibility checker and PDF tagging, to help with accessibility. But no PDF checker checks for incorrect tags, untagged content, or validates lists or tables. None check executable content at all. The "Halting Problem" is: can one decide whether a program will ever stop? The answer, in general, is no (Rice's theorem). The same holds true for accessibility checkers. Language-theoretic Security says complicated data formats are hard to parse and cannot be solved due to the Halting Problem. W3C Web Accessibility Guidelines: "Perceivable, Operable, Understandable, Robust" Not much help though, except for "Robust", but here's some gems: * all information should be parsable (paraphrasing) * if not parsable, cannot be converted to alternate formats * maximize compatibility in new document formats Executible webpages are bad for security and accessibility. They say it's for a better web experience. But is it necessary to stuff web pages with JavaScript for a better experience? A good example is The Drudge Report—it has hand-written HTML with no JavaScript, yet drives a lot of web traffic due to good content. A bad example is Google News—hidden scrollbars, guessing user input. Solutions: Accessibility and security problems come from same source Expose "better user experience" myth Keep your corner of Internet parsable Remember "Halting Problem"—recognize false solutions (checking and verifying tools) Stop Patching, for Stronger PCI Compliance Adam Brand, protiviti @adamrbrand, http://www.picfun.com/ Adam talked about PCI compliance for retail sales. Take an example: for PCI compliance, 50% of Brian's time (a IT guy), 960 hours/year was spent patching POSs in 850 restaurants. Often applying some patches make no sense (like fixing a browser vulnerability on a server). "Scanner worship" is overuse of vulnerability scanners—it gives a warm and fuzzy and it's simple (red or green results—fix reds). Scanners give a false sense of security. In reality, breeches from missing patches are uncommon—more common problems are: default passwords, cleartext authentication, misconfiguration (firewall ports open). Patching Myths: Myth 1: install within 30 days of patch release (but PCI §6.1 allows a "risk-based approach" instead). Myth 2: vendor decides what's critical (also PCI §6.1). But §6.2 requires user ranking of vulnerabilities instead. Myth 3: scan and rescan until it passes. But PCI §11.2.1b says this applies only to high-risk vulnerabilities. Adam says good recommendations come from NIST 800-40. Instead use sane patching and focus on what's really important. From NIST 800-40: Proactive: Use a proactive vulnerability management process: use change control, configuration management, monitor file integrity. Monitor: start with NVD and other vulnerability alerts, not scanner results. Evaluate: public-facing system? workstation? internal server? (risk rank) Decide:on action and timeline Test: pre-test patches (stability, functionality, rollback) for change control Install: notify, change control, tickets McAfee Secure & Trustmarks — a Hacker's Best Friend Jay James, Shane MacDougall, Tactical Intelligence Inc., Canada "McAfee Secure Trustmark" is a website seal marketed by McAfee. A website gets this badge if they pass their remote scanning. The problem is a removal of trustmarks act as flags that you're vulnerable. Easy to view status change by viewing McAfee list on website or on Google. "Secure TrustGuard" is similar to McAfee. Jay and Shane wrote Perl scripts to gather sites from McAfee and search engines. If their certification image changes to a 1x1 pixel image, then they are longer certified. Their scripts take deltas of scans to see what changed daily. The bottom line is change in TrustGuard status is a flag for hackers to attack your site. Entire idea of seals is silly—you're raising a flag saying if you're vulnerable.

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  • C#/.NET Little Wonders: The ConcurrentDictionary

    - by James Michael Hare
    Once again we consider some of the lesser known classes and keywords of C#.  In this series of posts, we will discuss how the concurrent collections have been developed to help alleviate these multi-threading concerns.  Last week’s post began with a general introduction and discussed the ConcurrentStack<T> and ConcurrentQueue<T>.  Today's post discusses the ConcurrentDictionary<T> (originally I had intended to discuss ConcurrentBag this week as well, but ConcurrentDictionary had enough information to create a very full post on its own!).  Finally next week, we shall close with a discussion of the ConcurrentBag<T> and BlockingCollection<T>. For more of the "Little Wonders" posts, see the index here. Recap As you'll recall from the previous post, the original collections were object-based containers that accomplished synchronization through a Synchronized member.  While these were convenient because you didn't have to worry about writing your own synchronization logic, they were a bit too finely grained and if you needed to perform multiple operations under one lock, the automatic synchronization didn't buy much. With the advent of .NET 2.0, the original collections were succeeded by the generic collections which are fully type-safe, but eschew automatic synchronization.  This cuts both ways in that you have a lot more control as a developer over when and how fine-grained you want to synchronize, but on the other hand if you just want simple synchronization it creates more work. With .NET 4.0, we get the best of both worlds in generic collections.  A new breed of collections was born called the concurrent collections in the System.Collections.Concurrent namespace.  These amazing collections are fine-tuned to have best overall performance for situations requiring concurrent access.  They are not meant to replace the generic collections, but to simply be an alternative to creating your own locking mechanisms. Among those concurrent collections were the ConcurrentStack<T> and ConcurrentQueue<T> which provide classic LIFO and FIFO collections with a concurrent twist.  As we saw, some of the traditional methods that required calls to be made in a certain order (like checking for not IsEmpty before calling Pop()) were replaced in favor of an umbrella operation that combined both under one lock (like TryPop()). Now, let's take a look at the next in our series of concurrent collections!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. ConcurrentDictionary – the fully thread-safe dictionary The ConcurrentDictionary<TKey,TValue> is the thread-safe counterpart to the generic Dictionary<TKey, TValue> collection.  Obviously, both are designed for quick – O(1) – lookups of data based on a key.  If you think of algorithms where you need lightning fast lookups of data and don’t care whether the data is maintained in any particular ordering or not, the unsorted dictionaries are generally the best way to go. Note: as a side note, there are sorted implementations of IDictionary, namely SortedDictionary and SortedList which are stored as an ordered tree and a ordered list respectively.  While these are not as fast as the non-sorted dictionaries – they are O(log2 n) – they are a great combination of both speed and ordering -- and still greatly outperform a linear search. Now, once again keep in mind that if all you need to do is load a collection once and then allow multi-threaded reading you do not need any locking.  Examples of this tend to be situations where you load a lookup or translation table once at program start, then keep it in memory for read-only reference.  In such cases locking is completely non-productive. However, most of the time when we need a concurrent dictionary we are interleaving both reads and updates.  This is where the ConcurrentDictionary really shines!  It achieves its thread-safety with no common lock to improve efficiency.  It actually uses a series of locks to provide concurrent updates, and has lockless reads!  This means that the ConcurrentDictionary gets even more efficient the higher the ratio of reads-to-writes you have. ConcurrentDictionary and Dictionary differences For the most part, the ConcurrentDictionary<TKey,TValue> behaves like it’s Dictionary<TKey,TValue> counterpart with a few differences.  Some notable examples of which are: Add() does not exist in the concurrent dictionary. This means you must use TryAdd(), AddOrUpdate(), or GetOrAdd().  It also means that you can’t use a collection initializer with the concurrent dictionary. TryAdd() replaced Add() to attempt atomic, safe adds. Because Add() only succeeds if the item doesn’t already exist, we need an atomic operation to check if the item exists, and if not add it while still under an atomic lock. TryUpdate() was added to attempt atomic, safe updates. If we want to update an item, we must make sure it exists first and that the original value is what we expected it to be.  If all these are true, we can update the item under one atomic step. TryRemove() was added to attempt atomic, safe removes. To safely attempt to remove a value we need to see if the key exists first, this checks for existence and removes under an atomic lock. AddOrUpdate() was added to attempt an thread-safe “upsert”. There are many times where you want to insert into a dictionary if the key doesn’t exist, or update the value if it does.  This allows you to make a thread-safe add-or-update. GetOrAdd() was added to attempt an thread-safe query/insert. Sometimes, you want to query for whether an item exists in the cache, and if it doesn’t insert a starting value for it.  This allows you to get the value if it exists and insert if not. Count, Keys, Values properties take a snapshot of the dictionary. Accessing these properties may interfere with add and update performance and should be used with caution. ToArray() returns a static snapshot of the dictionary. That is, the dictionary is locked, and then copied to an array as a O(n) operation.  GetEnumerator() is thread-safe and efficient, but allows dirty reads. Because reads require no locking, you can safely iterate over the contents of the dictionary.  The only downside is that, depending on timing, you may get dirty reads. Dirty reads during iteration The last point on GetEnumerator() bears some explanation.  Picture a scenario in which you call GetEnumerator() (or iterate using a foreach, etc.) and then, during that iteration the dictionary gets updated.  This may not sound like a big deal, but it can lead to inconsistent results if used incorrectly.  The problem is that items you already iterated over that are updated a split second after don’t show the update, but items that you iterate over that were updated a split second before do show the update.  Thus you may get a combination of items that are “stale” because you iterated before the update, and “fresh” because they were updated after GetEnumerator() but before the iteration reached them. Let’s illustrate with an example, let’s say you load up a concurrent dictionary like this: 1: // load up a dictionary. 2: var dictionary = new ConcurrentDictionary<string, int>(); 3:  4: dictionary["A"] = 1; 5: dictionary["B"] = 2; 6: dictionary["C"] = 3; 7: dictionary["D"] = 4; 8: dictionary["E"] = 5; 9: dictionary["F"] = 6; Then you have one task (using the wonderful TPL!) to iterate using dirty reads: 1: // attempt iteration in a separate thread 2: var iterationTask = new Task(() => 3: { 4: // iterates using a dirty read 5: foreach (var pair in dictionary) 6: { 7: Console.WriteLine(pair.Key + ":" + pair.Value); 8: } 9: }); And one task to attempt updates in a separate thread (probably): 1: // attempt updates in a separate thread 2: var updateTask = new Task(() => 3: { 4: // iterates, and updates the value by one 5: foreach (var pair in dictionary) 6: { 7: dictionary[pair.Key] = pair.Value + 1; 8: } 9: }); Now that we’ve done this, we can fire up both tasks and wait for them to complete: 1: // start both tasks 2: updateTask.Start(); 3: iterationTask.Start(); 4:  5: // wait for both to complete. 6: Task.WaitAll(updateTask, iterationTask); Now, if I you didn’t know about the dirty reads, you may have expected to see the iteration before the updates (such as A:1, B:2, C:3, D:4, E:5, F:6).  However, because the reads are dirty, we will quite possibly get a combination of some updated, some original.  My own run netted this result: 1: F:6 2: E:6 3: D:5 4: C:4 5: B:3 6: A:2 Note that, of course, iteration is not in order because ConcurrentDictionary, like Dictionary, is unordered.  Also note that both E and F show the value 6.  This is because the output task reached F before the update, but the updates for the rest of the items occurred before their output (probably because console output is very slow, comparatively). If we want to always guarantee that we will get a consistent snapshot to iterate over (that is, at the point we ask for it we see precisely what is in the dictionary and no subsequent updates during iteration), we should iterate over a call to ToArray() instead: 1: // attempt iteration in a separate thread 2: var iterationTask = new Task(() => 3: { 4: // iterates using a dirty read 5: foreach (var pair in dictionary.ToArray()) 6: { 7: Console.WriteLine(pair.Key + ":" + pair.Value); 8: } 9: }); The atomic Try…() methods As you can imagine TryAdd() and TryRemove() have few surprises.  Both first check the existence of the item to determine if it can be added or removed based on whether or not the key currently exists in the dictionary: 1: // try add attempts an add and returns false if it already exists 2: if (dictionary.TryAdd("G", 7)) 3: Console.WriteLine("G did not exist, now inserted with 7"); 4: else 5: Console.WriteLine("G already existed, insert failed."); TryRemove() also has the virtue of returning the value portion of the removed entry matching the given key: 1: // attempt to remove the value, if it exists it is removed and the original is returned 2: int removedValue; 3: if (dictionary.TryRemove("C", out removedValue)) 4: Console.WriteLine("Removed C and its value was " + removedValue); 5: else 6: Console.WriteLine("C did not exist, remove failed."); Now TryUpdate() is an interesting creature.  You might think from it’s name that TryUpdate() first checks for an item’s existence, and then updates if the item exists, otherwise it returns false.  Well, note quite... It turns out when you call TryUpdate() on a concurrent dictionary, you pass it not only the new value you want it to have, but also the value you expected it to have before the update.  If the item exists in the dictionary, and it has the value you expected, it will update it to the new value atomically and return true.  If the item is not in the dictionary or does not have the value you expected, it is not modified and false is returned. 1: // attempt to update the value, if it exists and if it has the expected original value 2: if (dictionary.TryUpdate("G", 42, 7)) 3: Console.WriteLine("G existed and was 7, now it's 42."); 4: else 5: Console.WriteLine("G either didn't exist, or wasn't 7."); The composite Add methods The ConcurrentDictionary also has composite add methods that can be used to perform updates and gets, with an add if the item is not existing at the time of the update or get. The first of these, AddOrUpdate(), allows you to add a new item to the dictionary if it doesn’t exist, or update the existing item if it does.  For example, let’s say you are creating a dictionary of counts of stock ticker symbols you’ve subscribed to from a market data feed: 1: public sealed class SubscriptionManager 2: { 3: private readonly ConcurrentDictionary<string, int> _subscriptions = new ConcurrentDictionary<string, int>(); 4:  5: // adds a new subscription, or increments the count of the existing one. 6: public void AddSubscription(string tickerKey) 7: { 8: // add a new subscription with count of 1, or update existing count by 1 if exists 9: var resultCount = _subscriptions.AddOrUpdate(tickerKey, 1, (symbol, count) => count + 1); 10:  11: // now check the result to see if we just incremented the count, or inserted first count 12: if (resultCount == 1) 13: { 14: // subscribe to symbol... 15: } 16: } 17: } Notice the update value factory Func delegate.  If the key does not exist in the dictionary, the add value is used (in this case 1 representing the first subscription for this symbol), but if the key already exists, it passes the key and current value to the update delegate which computes the new value to be stored in the dictionary.  The return result of this operation is the value used (in our case: 1 if added, existing value + 1 if updated). Likewise, the GetOrAdd() allows you to attempt to retrieve a value from the dictionary, and if the value does not currently exist in the dictionary it will insert a value.  This can be handy in cases where perhaps you wish to cache data, and thus you would query the cache to see if the item exists, and if it doesn’t you would put the item into the cache for the first time: 1: public sealed class PriceCache 2: { 3: private readonly ConcurrentDictionary<string, double> _cache = new ConcurrentDictionary<string, double>(); 4:  5: // adds a new subscription, or increments the count of the existing one. 6: public double QueryPrice(string tickerKey) 7: { 8: // check for the price in the cache, if it doesn't exist it will call the delegate to create value. 9: return _cache.GetOrAdd(tickerKey, symbol => GetCurrentPrice(symbol)); 10: } 11:  12: private double GetCurrentPrice(string tickerKey) 13: { 14: // do code to calculate actual true price. 15: } 16: } There are other variations of these two methods which vary whether a value is provided or a factory delegate, but otherwise they work much the same. Oddities with the composite Add methods The AddOrUpdate() and GetOrAdd() methods are totally thread-safe, on this you may rely, but they are not atomic.  It is important to note that the methods that use delegates execute those delegates outside of the lock.  This was done intentionally so that a user delegate (of which the ConcurrentDictionary has no control of course) does not take too long and lock out other threads. This is not necessarily an issue, per se, but it is something you must consider in your design.  The main thing to consider is that your delegate may get called to generate an item, but that item may not be the one returned!  Consider this scenario: A calls GetOrAdd and sees that the key does not currently exist, so it calls the delegate.  Now thread B also calls GetOrAdd and also sees that the key does not currently exist, and for whatever reason in this race condition it’s delegate completes first and it adds its new value to the dictionary.  Now A is done and goes to get the lock, and now sees that the item now exists.  In this case even though it called the delegate to create the item, it will pitch it because an item arrived between the time it attempted to create one and it attempted to add it. Let’s illustrate, assume this totally contrived example program which has a dictionary of char to int.  And in this dictionary we want to store a char and it’s ordinal (that is, A = 1, B = 2, etc).  So for our value generator, we will simply increment the previous value in a thread-safe way (perhaps using Interlocked): 1: public static class Program 2: { 3: private static int _nextNumber = 0; 4:  5: // the holder of the char to ordinal 6: private static ConcurrentDictionary<char, int> _dictionary 7: = new ConcurrentDictionary<char, int>(); 8:  9: // get the next id value 10: public static int NextId 11: { 12: get { return Interlocked.Increment(ref _nextNumber); } 13: } Then, we add a method that will perform our insert: 1: public static void Inserter() 2: { 3: for (int i = 0; i < 26; i++) 4: { 5: _dictionary.GetOrAdd((char)('A' + i), key => NextId); 6: } 7: } Finally, we run our test by starting two tasks to do this work and get the results… 1: public static void Main() 2: { 3: // 3 tasks attempting to get/insert 4: var tasks = new List<Task> 5: { 6: new Task(Inserter), 7: new Task(Inserter) 8: }; 9:  10: tasks.ForEach(t => t.Start()); 11: Task.WaitAll(tasks.ToArray()); 12:  13: foreach (var pair in _dictionary.OrderBy(p => p.Key)) 14: { 15: Console.WriteLine(pair.Key + ":" + pair.Value); 16: } 17: } If you run this with only one task, you get the expected A:1, B:2, ..., Z:26.  But running this in parallel you will get something a bit more complex.  My run netted these results: 1: A:1 2: B:3 3: C:4 4: D:5 5: E:6 6: F:7 7: G:8 8: H:9 9: I:10 10: J:11 11: K:12 12: L:13 13: M:14 14: N:15 15: O:16 16: P:17 17: Q:18 18: R:19 19: S:20 20: T:21 21: U:22 22: V:23 23: W:24 24: X:25 25: Y:26 26: Z:27 Notice that B is 3?  This is most likely because both threads attempted to call GetOrAdd() at roughly the same time and both saw that B did not exist, thus they both called the generator and one thread got back 2 and the other got back 3.  However, only one of those threads can get the lock at a time for the actual insert, and thus the one that generated the 3 won and the 3 was inserted and the 2 got discarded.  This is why on these methods your factory delegates should be careful not to have any logic that would be unsafe if the value they generate will be pitched in favor of another item generated at roughly the same time.  As such, it is probably a good idea to keep those generators as stateless as possible. Summary The ConcurrentDictionary is a very efficient and thread-safe version of the Dictionary generic collection.  It has all the benefits of type-safety that it’s generic collection counterpart does, and in addition is extremely efficient especially when there are more reads than writes concurrently. Tweet Technorati Tags: C#, .NET, Concurrent Collections, Collections, Little Wonders, Black Rabbit Coder,James Michael Hare

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  • Cannot boot from USB on my Mac mini

    - by Thai Tran
    Two weeks ago I installed OSX 10.8 on my Mac mini. After that, my system started to hang a lot, so I tried to erase it and install OSX 10.7 again. I used carbon Copy Cloner to make the bootable USB and it can load successfully on another Macbook. However, on my Mac mini, when I press on the option button to select the USB, it loads the white screen with a ban symbol at the center of the screen. After a moment, my machine automatically shuts down. Does anyone know how to solve this problem? Edit: this is exactly the problem I have now http://forums.macrumors.com/archive/index.php/t-1207168.html Update 1: the hdd seems ok (from disk utility). I restored the booting partition by disk utility (drag the dmg file to that partition). After restarting and using that partition to boot, prohibited symbol is still there

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  • Arguments passed on by shell to command in Unix

    - by Ryan Brown
    I've been going over this question and I can't for the life of me figure out why the answer is what it is. How many arguments are passed to the command by the shell on this command line:<pig pig -x " " -z -r" " >pig pig pig a. 8 b. 6 c. 5 d. 7 e. 9 The first symbol is supposed to be the symbol for redirected input but the site isn't letting me use it. [Fixed.] I looked at this question and said ok...arguments...not options so 2nd pig, then " ", then -r" ", 4th pig and 5th pig...-z and -x are options, so I count 5. The answer is b. 6. Where is the 6th argument that's being passed on?

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  • MacVim, Command-T: SEGV

    - by Ramon Tayag
    Details: OSX 10.7.4 I installed the latest MacVim via Homebrew: $ command-t brew install macvim ==> Downloading https://github.com/b4winckler/macvim/tarball/snapshot-64 Already downloaded: /Library/Caches/Homebrew/macvim-7.3-64.tgz ==> ./configure --with-features=huge --with-tlib=ncurses --enable-multibyte --with-macarchs=x86_64 --enable-perlinterp --enable-pythoninterp --enable-rubyinterp --enable-t ==> make getenvy ==> make ==> Caveats MacVim.app installed to: /usr/local/Cellar/macvim/7.3-64 To link the application to a normal Mac OS X location: brew linkapps or: ln -s /usr/local/Cellar/macvim/7.3-64/MacVim.app /Applications ==> Summary /usr/local/Cellar/macvim/7.3-64: 1733 files, 27M, built in 53 seconds $ command-t brew linkapps Linking /usr/local/Cellar/macvim/7.3-64/MacVim.app Finished linking. Find the links under ~/Applications. $ command-t ruby -v ruby 1.8.7 (2011-12-28 patchlevel 357) [universal-darwin11.0] $ command-t rvm list rvm rubies ree-1.8.7-2012.02 [ i686 ] ruby-1.8.7-p358 [ i686 ] ruby-1.9.2-p290 [ x86_64 ] ruby-1.9.2-p320 [ x86_64 ] ruby-1.9.3-p194 [ x86_64 ] # Default ruby not set. Try 'rvm alias create default <ruby>'. # => - current # =* - current && default # * - default $ command-t cd ~/.vim/bundle/vim-command-t/ruby/command-t ruby extconf.rb $ command-t ruby extconf.rb checking for ruby.h... yes creating Makefile $ command-t make cc -arch i386 -arch x86_64 -pipe -bundle -undefined dynamic_lookup -o ext.bundle ext.o match.o matcher.o -L. -L/System/Library/Frameworks/Ruby.framework/Versions/1.8/usr/lib -L. -arch i386 -arch x86_64 -lruby -lpthread -ldl -lobjc ld: warning: ignoring file ext.o, file was built for unsupported file format which is not the architecture being linked (i386) ld: warning: ignoring file match.o, file was built for unsupported file format which is not the architecture being linked (i386) ld: warning: ignoring file matcher.o, file was built for unsupported file format which is not the architecture being linked (i386) $ command-t mvim MacVim then opens here. But when I open Command-T, MacVim crashes and I see this in the command line: $ command-t dyld: lazy symbol binding failed: Symbol not found: _rb_intern2 Referenced from: /Users/ramon/.vim/bundle/vim-command-t/ruby/command-t/ext.bundle Expected in: flat namespace dyld: Symbol not found: _rb_intern2 Referenced from: /Users/ramon/.vim/bundle/vim-command-t/ruby/command-t/ext.bundle Expected in: flat namespace Vim: Caught deadly signal TRAP Vim: Finished. The problem I have is very similar to this, except that I switched to the system Ruby and still got the error.

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  • Have VIM jump to a ctag in an existing tab

    - by Adrian Petrescu
    I have ctags configured with my vim installation. My habit is to usually have all of the relevant files I'm working on open in tabs in vim all at once. The "problem" is that if I use Ctrl+] to jump to a ctag in a file I'm editing, it will replace the buffer in that tab, even though I have another tab already open containing that symbol. It would be much better if it just switched to that tab and jumped to the symbol there instead. This way I would always have a 1-to-1 tab-to-file ratio. I noticed in the Changenotes for the taglist.vim plugin (which I also use) has an entry that says 1. Added support for jumping to a tag/file in a new or existing tab from the taglist window (works only with Vim7 and above). However, I couldn't find anything in the documentation for Taglist (or Ctags) about how to actually do this. Can any vim gurus fill me in? Thanks!

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  • DBD::mysql gives mysql_init not found

    - by highBandWidth
    I have to install a non-admin copy of mysql and perl module DBD::mysql in my home directory. I installed mysql in ~/software/db/mysql and this works since I can start and stop the server and go to the mysql prompt. Then, I downloaded the perl module and installed it using perl Makefile.PL PREFIX=~/myperl/ LIB=~/myperl/lib/lib64/perl5/ --mysql_config=/my_home/software/db/mysql/bin/mysql_config --libs=/myhome/software/db/mysql/lib/libmysqlclient.a make make install I did this to use the statically linked mysql client library. perl -MDBD::mysql -e 1 gives no errors. However, when I actually try to use the module, I get /usr/bin/perl: symbol lookup error: /myhome/myperl/lib/lib64/perl5/x86_64-linux-thread-multi/auto/DBD/mysql/mysql.so: undefined symbol: mysql_init

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  • What does % mean in linux / how to install jmf

    - by Ben
    I am fairly new to linux and am using fedora 14 (64 bit). I have to install the java media framework for one of my projects. In the installation instructions on their website (http://www.oracle.com/technetwork/java/javase/download-142937.html) they use the % symbol. I have done some research and googling and can't find what the significance of % is. Does anyone know? I have been able to find just about every other symbol meaning (., .., #, and more). They use it in the following context Run the command % /bin/sh ./jmf-2_1_1e-linux-i586.bin

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  • How to send a pipe with psexec?

    - by Pierre-Alain Vigeant
    I'm trying to execute a pipe on a remote server by using psexec. The command that I'm trying to execute is psexec \\servername DSQUERY USER -name *userpart* | DSGET USER -samid -display Currently, the | pipe symbol get executed locally which is not what is wanted (since dsget does not exist on my machine). I tried to use quote around the whole command psexec \\servername "DSQUERY USER -name *userpart* | DSGET USER -samid -display" but that resulted in psexec trying to run that whole quoted sentence as one executable, which obviously does not exist. How can I pass a pipe symbol to the remote server so that it can execute it?

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  • Keyboard glitches for some when Ctrl key is pressed

    - by user270716
    I'm having some problems with my keyboard, if I press the Ctrl key it glitches for some time. For example, if I press Ctrl and press Tab while it's still glitched the computer shuts down as if i pressed the Power On/Off button. If I press a it "presses" Alt, A and a symbol I can't remember, if I recall correctly it's a currency symbol. If I press Ctrl again it "presses" the ' key. I'm using Windows 8 Single Language 64 bits with a ABNT2 keyboard. The processor is a Intel Celeron G530 with 2 GB of RAM.

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  • error LNK2019 for ZLib sample compare.

    - by Nano HE
    Hello. I created win32 console application in vs2010 (without select the option of precompiled header). And I inserted the code below. but *.obj link failed. Could you provide me more information about the error. I searched MSDN, but still can't understand it. #include <stdio.h> #include "zlib.h" // Demonstration of zlib utility functions unsigned long file_size(char *filename) { FILE *pFile = fopen(filename, "rb"); fseek (pFile, 0, SEEK_END); unsigned long size = ftell(pFile); fclose (pFile); return size; } int decompress_one_file(char *infilename, char *outfilename) { gzFile infile = gzopen(infilename, "rb"); FILE *outfile = fopen(outfilename, "wb"); if (!infile || !outfile) return -1; char buffer[128]; int num_read = 0; while ((num_read = gzread(infile, buffer, sizeof(buffer))) > 0) { fwrite(buffer, 1, num_read, outfile); } gzclose(infile); fclose(outfile); } int compress_one_file(char *infilename, char *outfilename) { FILE *infile = fopen(infilename, "rb"); gzFile outfile = gzopen(outfilename, "wb"); if (!infile || !outfile) return -1; char inbuffer[128]; int num_read = 0; unsigned long total_read = 0, total_wrote = 0; while ((num_read = fread(inbuffer, 1, sizeof(inbuffer), infile)) > 0) { total_read += num_read; gzwrite(outfile, inbuffer, num_read); } fclose(infile); gzclose(outfile); printf("Read %ld bytes, Wrote %ld bytes, Compression factor %4.2f%%\n", total_read, file_size(outfilename), (1.0-file_size(outfilename)*1.0/total_read)*100.0); } int main(int argc, char **argv) { compress_one_file(argv[1],argv[2]); decompress_one_file(argv[2],argv[3]);} Output: 1>------ Build started: Project: zlibApp, Configuration: Debug Win32 ------ 1> zlibApp.cpp 1>d:\learning\cpp\cppvs2010\zlibapp\zlibapp\zlibapp.cpp(15): warning C4996: 'fopen': This function or variable may be unsafe. Consider using fopen_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS. See online help for details. 1> c:\program files\microsoft visual studio 10.0\vc\include\stdio.h(234) : see declaration of 'fopen' 1>d:\learning\cpp\cppvs2010\zlibapp\zlibapp\zlibapp.cpp(25): warning C4996: 'fopen': This function or variable may be unsafe. Consider using fopen_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS. See online help for details. 1> c:\program files\microsoft visual studio 10.0\vc\include\stdio.h(234) : see declaration of 'fopen' 1>d:\learning\cpp\cppvs2010\zlibapp\zlibapp\zlibapp.cpp(40): warning C4996: 'fopen': This function or variable may be unsafe. Consider using fopen_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS. See online help for details. 1> c:\program files\microsoft visual studio 10.0\vc\include\stdio.h(234) : see declaration of 'fopen' 1>d:\learning\cpp\cppvs2010\zlibapp\zlibapp\zlibapp.cpp(36): warning C4715: 'decompress_one_file' : not all control paths return a value 1>d:\learning\cpp\cppvs2010\zlibapp\zlibapp\zlibapp.cpp(57): warning C4715: 'compress_one_file' : not all control paths return a value 1>zlibApp.obj : error LNK2019: unresolved external symbol _gzclose referenced in function "int __cdecl decompress_one_file(char *,char *)" (?decompress_one_file@@YAHPAD0@Z) 1>zlibApp.obj : error LNK2019: unresolved external symbol _gzread referenced in function "int __cdecl decompress_one_file(char *,char *)" (?decompress_one_file@@YAHPAD0@Z) 1>zlibApp.obj : error LNK2019: unresolved external symbol _gzopen referenced in function "int __cdecl decompress_one_file(char *,char *)" (?decompress_one_file@@YAHPAD0@Z) 1>zlibApp.obj : error LNK2019: unresolved external symbol _gzwrite referenced in function "int __cdecl compress_one_file(char *,char *)" (?compress_one_file@@YAHPAD0@Z) 1>D:\learning\cpp\cppVS2010\zlibApp\Debug\zlibApp.exe : fatal error LNK1120: 4 unresolved externals ========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

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  • error LNK2019 for ZLib sample code compiling.

    - by Nano HE
    Hello. I created win32 console application in vs2010 (without select the option of precompiled header). And I inserted the code below. but *.obj link failed. Could you provide me more information about the error. I searched MSDN, but still can't understand it. #include <stdio.h> #include "zlib.h" // Demonstration of zlib utility functions unsigned long file_size(char *filename) { FILE *pFile = fopen(filename, "rb"); fseek (pFile, 0, SEEK_END); unsigned long size = ftell(pFile); fclose (pFile); return size; } int decompress_one_file(char *infilename, char *outfilename) { gzFile infile = gzopen(infilename, "rb"); FILE *outfile = fopen(outfilename, "wb"); if (!infile || !outfile) return -1; char buffer[128]; int num_read = 0; while ((num_read = gzread(infile, buffer, sizeof(buffer))) > 0) { fwrite(buffer, 1, num_read, outfile); } gzclose(infile); fclose(outfile); } int compress_one_file(char *infilename, char *outfilename) { FILE *infile = fopen(infilename, "rb"); gzFile outfile = gzopen(outfilename, "wb"); if (!infile || !outfile) return -1; char inbuffer[128]; int num_read = 0; unsigned long total_read = 0, total_wrote = 0; while ((num_read = fread(inbuffer, 1, sizeof(inbuffer), infile)) > 0) { total_read += num_read; gzwrite(outfile, inbuffer, num_read); } fclose(infile); gzclose(outfile); printf("Read %ld bytes, Wrote %ld bytes, Compression factor %4.2f%%\n", total_read, file_size(outfilename), (1.0-file_size(outfilename)*1.0/total_read)*100.0); } int main(int argc, char **argv) { compress_one_file(argv[1],argv[2]); decompress_one_file(argv[2],argv[3]);} Output: 1>------ Build started: Project: zlibApp, Configuration: Debug Win32 ------ 1> zlibApp.cpp 1>d:\learning\cpp\cppvs2010\zlibapp\zlibapp\zlibapp.cpp(15): warning C4996: 'fopen': This function or variable may be unsafe. Consider using fopen_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS. See online help for details. 1> c:\program files\microsoft visual studio 10.0\vc\include\stdio.h(234) : see declaration of 'fopen' 1>d:\learning\cpp\cppvs2010\zlibapp\zlibapp\zlibapp.cpp(25): warning C4996: 'fopen': This function or variable may be unsafe. Consider using fopen_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS. See online help for details. 1> c:\program files\microsoft visual studio 10.0\vc\include\stdio.h(234) : see declaration of 'fopen' 1>d:\learning\cpp\cppvs2010\zlibapp\zlibapp\zlibapp.cpp(40): warning C4996: 'fopen': This function or variable may be unsafe. Consider using fopen_s instead. To disable deprecation, use _CRT_SECURE_NO_WARNINGS. See online help for details. 1> c:\program files\microsoft visual studio 10.0\vc\include\stdio.h(234) : see declaration of 'fopen' 1>d:\learning\cpp\cppvs2010\zlibapp\zlibapp\zlibapp.cpp(36): warning C4715: 'decompress_one_file' : not all control paths return a value 1>d:\learning\cpp\cppvs2010\zlibapp\zlibapp\zlibapp.cpp(57): warning C4715: 'compress_one_file' : not all control paths return a value 1>zlibApp.obj : error LNK2019: unresolved external symbol _gzclose referenced in function "int __cdecl decompress_one_file(char *,char *)" (?decompress_one_file@@YAHPAD0@Z) 1>zlibApp.obj : error LNK2019: unresolved external symbol _gzread referenced in function "int __cdecl decompress_one_file(char *,char *)" (?decompress_one_file@@YAHPAD0@Z) 1>zlibApp.obj : error LNK2019: unresolved external symbol _gzopen referenced in function "int __cdecl decompress_one_file(char *,char *)" (?decompress_one_file@@YAHPAD0@Z) 1>zlibApp.obj : error LNK2019: unresolved external symbol _gzwrite referenced in function "int __cdecl compress_one_file(char *,char *)" (?compress_one_file@@YAHPAD0@Z) 1>D:\learning\cpp\cppVS2010\zlibApp\Debug\zlibApp.exe : fatal error LNK1120: 4 unresolved externals ========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

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  • Text contains characters that cannot be resolved by this SpriteFont

    - by Appeltaart
    I'm trying to draw currency symbols in an Arial Spritefont. According to thissite, the font contains these symbols. I've included the Unicode character region for these symbols in the Content Processor SpriteFont file, like so: <CharacterRegions> <CharacterRegion> <Start>&#32;</Start> <End>&#126;</End> </CharacterRegion> <CharacterRegion> <!-- Currency symbols --> <Start>&#8352;</Start> <End>&#8378;</End> </CharacterRegion> </CharacterRegions> However, whenever I try to draw a € (Euro) symbol, I get this exception: Text contains characters that cannot be resolved by this SpriteFont Inspecting the SpriteFont in the IDE at that breakpoint shows the € symbol is in there. I'm at a loss at what could be wrong. Why is this exception thrown?

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  • Issue While uploading a image to share point 2010 picture library.

    - by Gino Abraham
    I was trying to upload a image to my picture library using sharepoint client object model. I Used the code from the below blog to upload a file to my picture library. http://blogs.msdn.com/b/sridhara/archive/2010/03/12/uploading-files-using-client-object-model-in-sharepoint-2010.aspx The image got uploaded sucessfully. But when we took the relative url to update in a different list, we were getting empty image symbol. After a lot of analysis we figured out that the issue was with the file we uploaded. An image file which is of jpeg quality was uploaded to an application with giff extension. Try this. Copy a JPG file from net and save it to your file system. Change the extension of the file from jpg to giff. When you change the file extension the image quality remains same but it will open in picture viewers. Upload the file to your picture library. Once uploaded you will get the file listed as thumbail in your picture library. Click on the thumbnail image it will open up a page showing a larger image with file details. Now click either on the image or the file name hyper link, it will open up an empty page with default no image symbol. I wasted a lot of time on this figuring out the issue, so thought of sharing here. Hope this helps some one.

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  • What is an effective way to convert a shared memory-mapped system to another data access model?

    - by Rob Jones
    I have a code base that is designed around shared memory. Each process that needs to access the memory maps it into its own address space. The data structures in the shared memory are directly accessed, that is, there is no API. For example: Assume the following: typedef struct { int x; int y; struct { int a; int b; } z; } myStruct; myStruct s; Then a process might access this structure as: myStruct *s = mapGlobalMem(); And use it as: int tmpX = s->x; The majority of the information in the global structure is configuration information that is set once and read many times. I would like to store this information in a database and develop an API to access the database. The problem is, these references are sprinkled throughout the code. I need a way to parse the code and identify global structure references that will need to be refactored. I've looked into using ANTLR to create a parser that will identify references to a small set of structures and enter them into a custom symbol table. I could then use this symbol table to identify which source files need to be refactored. It looks like a promising approach. What other approaches are there? Of course, I'm looking for a programmatic approach. There are far too many source files to examine each one visually. This is all ordinary ANSI C. Nothing else.

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  • How to adjust the appearance of the Unity in 12.10?

    - by piedro
    Now I updated to 12.10 and would like to adjust the desktop, well unity, appearance. I know there is the theme setting, but I cannot adjust the symbol theme or windows decoration with the systemsettings. I used to use the tool "unsettings" but it doesn't work with 12.10 anymore. Ubuntu Tweak used to be an option but at this point many features are broken and a lot of settings seem to mess up my system or they don't change anything at all (I understand that there has been a design settings change - gsettings, dconf, something ...) myunity has some options to change stuff but I couldn't find it for 12.10 ... not to forget "gnome-tweak-tool" which seems to work for most settings but not for all, e.g. it doesn't change the mouse cursor and the windows decorations do not show some decorations I'd like to use and I am also afraid of messing things up because it is supposed to be used in gnomeshell ... actually as I found out right now it really messes things up: fonts get inverted, suddenly high contrast accessibility setings are used in some windows, nautilus has white fonts on white background and even the login manager is a mess now ... So: How can I adjust the theme, symbol, decorations, fonts for the normal user and for the desktop and for the applications including the applications started as sudo user? I should mention that I upgraded from 12.04 and that some applications like synaptic completely ignore any settings ... sadly it is a mess, there was a time when gnome theming was really well done and very adjustable, I wonder what happened ... Just now I read that further development of Ubuntu Tweak has been stopped. The developer announced that he won't go any further with the software and the online services ... That is sad and destroys my hope for easy appearance editing just by waiting ... has been such a nice tool for 12.04 ... r.i.p.

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  • Opengl + SDL linking error

    - by me2loveit2
    I am trying to load an image as a texture with opengl using c++ in visual studio 2010. I researched a couple hours online and found the SDL library, then I implemented a simple example and got some linking error I can not seem to figure out. The error log is here: 1Build started 10/20/2012 12:09:17 AM. 1InitializeBuildStatus: 1 Touching "Debug\texture mapping test.unsuccessfulbuild". 1ClCompile: 1 All outputs are up-to-date. 1 texture mapping test.cpp 1ManifestResourceCompile: 1 All outputs are up-to-date. 1texture mapping test.obj : error LNK2019: unresolved external symbol _IMG_Load referenced in function "void __cdecl display(void)" (?display@@YAXXZ) 1MSVCRTD.lib(crtexe.obj) : error LNK2019: unresolved external symbol main referenced in function __tmainCRTStartup 1C:\Users\Me\Documents\Visual Studio 2010\Projects\Programming projects\texture mapping test\Debug\texture mapping test.exe : fatal error LNK1120: 2 unresolved externals 1 1Build FAILED. 1 1Time Elapsed 00:00:02.45 ========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ========== Can someone please help me!! I am at a desperate point right now. I downloaded the SDL, and copied all the .h file into: C:\Program Files (x86)\Microsoft SDKs\Windows\v7.0A\Include I added the .lib (x86) files into://as a not i tried the (x64) file too but got the exact same error C:\Program Files (x86)\Microsoft SDKs\Windows\v7.0A\Lib and the .dll(x86) into: C:\Windows\System32 For implementing textures, I used the simple sample code from: http://www.sdltutorials.com/sdl-tip-sdl-surface-to-opengl-texture Please let me know if you can see me doing something wrong, or know how I can fix this!! Thanks Phil

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  • issues with ASUS S301L ultrabooks

    - by Wuerze
    I just like to tell you what still is a Problem in Ubuntu 14.04 and should be solved for a nice experience of this distribution. Unfortunately I do not have any hints to tell you, because I am just a user and know not much about programming. Anyway, I hope it helps. 1) Intel open source Graphics issues (proprietary) -when attaching HDMI-cable the screen switches to the external monitor and it's fine, but there is no switching back unless restart with HDMI deattached -black screen appears for like 2 seconds as if I would change screen in the settings; frequency increases with intensity of driver use (i.e. videos or video games) 2) hotkeys (commonly recognised) -there is no possibility to adjust brightness with the hotkeys (Fn+F5 and Fn+F6) 3) touchscreen (commonly recognised) -the touchscreen is behaving like a mouse -configuring gestures for the multi touch screen seems to always end in disabling touch pad gestures 4) panel symbols -battery symbol has got a low accuracy while it determines accurately the energy left; only 5 steps of energy are shown by the symbol Thank you all for participating in the solution of these problems! I will stay tuned and edit this list if something has been solved.

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  • How to read reduce/shift conflicts in LR(1) DFA?

    - by greenoldman
    I am reading an explanation (awesome "Parsing Techniques" by D.Grune and C.J.H.Jacobs; p.293 in the 2nd edition) and I moved forward from my last question: How to get lookahead symbol when constructing LR(1) NFA for parser? Now I have such "problem" (maybe not a problem, but rather need of confirmation from some more knowledgeable people). The authors present state in LR(0) which has reduce/shift conflict. Then they build DFA for LR(1) for the same grammar. And now they say it does not have a conflict (lookaheads at the end): S -> E . eof E -> E . - T eof E -> E . - T - and there is an edge from this state labeled - but no labeled eof. Authors says, that on eof there will be reduce, on - there will be shift. However eof is for shift as well (as lookahead). So my personal understanding of LR(1) DFA is this -- you can drop lookaheads for shifts, because they serve no purpose now -- shifts rely on input, not on lookaheads -- and after that, remove duplicates. S -> E . eof E -> E . - T So the lookahead for reduce serves as input really, because at this stage (all required input is read) it is really incoming symbol right now. For shifts, the input symbols are on the edges. So my question is this -- am I actually right about dropping lookaheads for shifts (after fully constructing DFA)?

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  • Can't get utouch to show available wifi networks

    - by kellrobinson
    I have ubuntu touch installed on a 2014 Nexus 7. Swiping down from the wireless symbol reveals a "Network" menu with the choices Flight Mode, Wifi Settings, and Cellular Settings. Wifi Settings leads to another menu: Previous Networks, and Other Networks. Previous Networks shows a list of networks used in the past; Other Networks opens an empty box for typing in the name of a network. I don't see any way to show a list of available networks detected by the device. On rare occasions, swiping down the wireless symbol actually does bring up a list of detected networks. But most of the time ubuntu touch exhibits the behavior described above, with no apparent way to bring up the list of available wireless networks. I would like to see a list of the availble networks, if there is a way to do so. Edit: The wifi menu works properly now. Just needed a couple of reboots, it seems. I have other problems, though. If these other problems persist I will make a post specific to them. This device is a 2013 Nexus 7 4G. Not sure how to find the ubuntu version. Can't navigate the settings menu right now because it got stuck and there's no way to go back, except to reboot(!) I'll open multirom manager or boot into recovery and look for the information there.

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  • Custom language - FOR loop in a clojure interpeter?

    - by Mark
    I have a basic interpreter in clojure. Now i need to implement for (initialisation; finish-test; loop-update) { statements } Implement a similar for-loop for the interpreted language. The pattern will be: (for variable-declarations end-test loop-update do statement) The variable-declarations will set up initial values for variables.The end-test returns a boolean, and the loop will end if end-test returns false. The statement is interpreted followed by the loop-update for each pass of the loop. Examples of use are: (run ’(for ((i 0)) (< i 10) (set i (+ 1 i)) do (println i))) (run ’(for ((i 0) (j 0)) (< i 10) (seq (set i (+ 1 i)) (set j (+ j (* 2 i)))) do (println j))) inside my interpreter. I will attach my interpreter code I got so far. Any help is appreciated. Interpreter (declare interpret make-env) ;; needed as language terms call out to 'interpret' (def do-trace false) ;; change to 'true' to show calls to 'interpret' ;; simple utilities (def third ; return third item in a list (fn [a-list] (second (rest a-list)))) (def fourth ; return fourth item in a list (fn [a-list] (third (rest a-list)))) (def run ; make it easy to test the interpreter (fn [e] (println "Processing: " e) (println "=> " (interpret e (make-env))))) ;; for the environment (def make-env (fn [] '())) (def add-var (fn [env var val] (cons (list var val) env))) (def lookup-var (fn [env var] (cond (empty? env) 'error (= (first (first env)) var) (second (first env)) :else (lookup-var (rest env) var)))) ;; for terms in language ;; -- define numbers (def is-number? (fn [expn] (number? expn))) (def interpret-number (fn [expn env] expn)) ;; -- define symbols (def is-symbol? (fn [expn] (symbol? expn))) (def interpret-symbol (fn [expn env] (lookup-var env expn))) ;; -- define boolean (def is-boolean? (fn [expn] (or (= expn 'true) (= expn 'false)))) (def interpret-boolean (fn [expn env] expn)) ;; -- define functions (def is-function? (fn [expn] (and (list? expn) (= 3 (count expn)) (= 'lambda (first expn))))) (def interpret-function ; keep function definitions as they are written (fn [expn env] expn)) ;; -- define addition (def is-plus? (fn [expn] (and (list? expn) (= 3 (count expn)) (= '+ (first expn))))) (def interpret-plus (fn [expn env] (+ (interpret (second expn) env) (interpret (third expn) env)))) ;; -- define subtraction (def is-minus? (fn [expn] (and (list? expn) (= 3 (count expn)) (= '- (first expn))))) (def interpret-minus (fn [expn env] (- (interpret (second expn) env) (interpret (third expn) env)))) ;; -- define multiplication (def is-times? (fn [expn] (and (list? expn) (= 3 (count expn)) (= '* (first expn))))) (def interpret-times (fn [expn env] (* (interpret (second expn) env) (interpret (third expn) env)))) ;; -- define division (def is-divides? (fn [expn] (and (list? expn) (= 3 (count expn)) (= '/ (first expn))))) (def interpret-divides (fn [expn env] (/ (interpret (second expn) env) (interpret (third expn) env)))) ;; -- define equals test (def is-equals? (fn [expn] (and (list? expn) (= 3 (count expn)) (= '= (first expn))))) (def interpret-equals (fn [expn env] (= (interpret (second expn) env) (interpret (third expn) env)))) ;; -- define greater-than test (def is-greater-than? (fn [expn] (and (list? expn) (= 3 (count expn)) (= '> (first expn))))) (def interpret-greater-than (fn [expn env] (> (interpret (second expn) env) (interpret (third expn) env)))) ;; -- define not (def is-not? (fn [expn] (and (list? expn) (= 2 (count expn)) (= 'not (first expn))))) (def interpret-not (fn [expn env] (not (interpret (second expn) env)))) ;; -- define or (def is-or? (fn [expn] (and (list? expn) (= 3 (count expn)) (= 'or (first expn))))) (def interpret-or (fn [expn env] (or (interpret (second expn) env) (interpret (third expn) env)))) ;; -- define and (def is-and? (fn [expn] (and (list? expn) (= 3 (count expn)) (= 'and (first expn))))) (def interpret-and (fn [expn env] (and (interpret (second expn) env) (interpret (third expn) env)))) ;; -- define print (def is-print? (fn [expn] (and (list? expn) (= 2 (count expn)) (= 'println (first expn))))) (def interpret-print (fn [expn env] (println (interpret (second expn) env)))) ;; -- define with (def is-with? (fn [expn] (and (list? expn) (= 3 (count expn)) (= 'with (first expn))))) (def interpret-with (fn [expn env] (interpret (third expn) (add-var env (first (second expn)) (interpret (second (second expn)) env))))) ;; -- define if (def is-if? (fn [expn] (and (list? expn) (= 4 (count expn)) (= 'if (first expn))))) (def interpret-if (fn [expn env] (cond (interpret (second expn) env) (interpret (third expn) env) :else (interpret (fourth expn) env)))) ;; -- define function-application (def is-function-application? (fn [expn env] (and (list? expn) (= 2 (count expn)) (is-function? (interpret (first expn) env))))) (def interpret-function-application (fn [expn env] (let [function (interpret (first expn) env)] (interpret (third function) (add-var env (first (second function)) (interpret (second expn) env)))))) ;; the interpreter itself (def interpret (fn [expn env] (cond do-trace (println "Interpret is processing: " expn)) (cond ; basic values (is-number? expn) (interpret-number expn env) (is-symbol? expn) (interpret-symbol expn env) (is-boolean? expn) (interpret-boolean expn env) (is-function? expn) (interpret-function expn env) ; built-in functions (is-plus? expn) (interpret-plus expn env) (is-minus? expn) (interpret-minus expn env) (is-times? expn) (interpret-times expn env) (is-divides? expn) (interpret-divides expn env) (is-equals? expn) (interpret-equals expn env) (is-greater-than? expn) (interpret-greater-than expn env) (is-not? expn) (interpret-not expn env) (is-or? expn) (interpret-or expn env) (is-and? expn) (interpret-and expn env) (is-print? expn) (interpret-print expn env) ; special syntax (is-with? expn) (interpret-with expn env) (is-if? expn) (interpret-if expn env) ; functions (is-function-application? expn env) (interpret-function-application expn env) :else 'error))) ;; tests of using environment (println "Environment tests:") (println (add-var (make-env) 'x 1)) (println (add-var (add-var (add-var (make-env) 'x 1) 'y 2) 'x 3)) (println (lookup-var '() 'x)) (println (lookup-var '((x 1)) 'x)) (println (lookup-var '((x 1) (y 2)) 'x)) (println (lookup-var '((x 1) (y 2)) 'y)) (println (lookup-var '((x 3) (y 2) (x 1)) 'x)) ;; examples of using interpreter (println "Interpreter examples:") (run '1) (run '2) (run '(+ 1 2)) (run '(/ (* (+ 4 5) (- 2 4)) 2)) (run '(with (x 1) x)) (run '(with (x 1) (with (y 2) (+ x y)))) (run '(with (x (+ 2 4)) x)) (run 'false) (run '(not false)) (run '(with (x true) (with (y false) (or x y)))) (run '(or (= 3 4) (> 4 3))) (run '(with (x 1) (if (= x 1) 2 3))) (run '(with (x 2) (if (= x 1) 2 3))) (run '((lambda (n) (* 2 n)) 4)) (run '(with (double (lambda (n) (* 2 n))) (double 4))) (run '(with (sum-to (lambda (n) (if (= n 0) 0 (+ n (sum-to (- n 1)))))) (sum-to 100))) (run '(with (x 1) (with (f (lambda (n) (+ n x))) (with (x 2) (println (f 3))))))

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  • ct.sym steals the ASM class

    - by Geertjan
    Some mild consternation on the Twittersphere yesterday. Marcus Lagergren not being able to find the ASM classes in JDK 8 in NetBeans IDE: And there's no such problem in Eclipse (and apparently in IntelliJ IDEA). Help, does NetBeans (despite being incredibly awesome) suck, after all? The truth of the matter is that there's something called "ct.sym" in the JDK. When javac is compiling code, it doesn't link against rt.jar. Instead, it uses a special symbol file lib/ct.sym with class stubs. Internal JDK classes are not put in that symbol file, since those are internal classes. You shouldn't want to use them, at all. However, what if you're Marcus Lagergren who DOES need these classes? I.e., he's working on the internal JDK classes and hence needs to have access to them. Fair enough that the general Java population can't access those classes, since they're internal implementation classes that could be changed anytime and one wouldn't want all unknown clients of those classes to start breaking once changes are made to the implementation, i.e., this is the rt.jar's internal class protection mechanism. But, again, we're now Marcus Lagergen and not the general Java population. For the solution, read Jan Lahoda, NetBeans Java Editor guru, here: https://netbeans.org/bugzilla/show_bug.cgi?id=186120 In particular, take note of this: AFAIK, the ct.sym is new in JDK6. It contains stubs for all classes that existed in JDK5 (for compatibility with existing programs that would use private JDK classes), but does not contain implementation classes that were introduced in JDK6 (only API classes). This is to prevent application developers to accidentally use JDK's private classes (as such applications would be unportable and may not run on future versions of JDK). Note that this is not really a NB thing - this is the behavior of javac from the JDK. I do not know about any way to disable this except deleting ct.sym or the option mentioned above. Regarding loading the classes: JVM uses two classpath's: classpath and bootclasspath. rt.jar is on the bootclasspath and has precedence over anything on the "custom" classpath, which is used by the application. The usual way to override classes on bootclasspath is to start the JVM with "-Xbootclasspath/p:" option, which prepends the given jars (and presumably also directories) to bootclasspath. Hence, let's take the first option, the simpler one, and simply delete the "ct.sym" file. Again, only because we need to work with those internal classes as developers of the JDK, not because we want to hack our way around "ct.sym", which would mean you'd not have portable code at the end of the day. Go to the JDK 8 lib folder and you'll find the file: Delete it. Start NetBeans IDE again, either on JDK 7 or JDK 8, doesn't make a difference for these purposes, create a new Java application (or use an existing one), make sure you have set the JDK above as the JDK of the application, and hey presto: The above obviously assumes you have a build of JDK 8 that actually includes the ASM package. And below you can see that not only are the classes found but my build succeeded, even though I'm using internal JDK classes. The yellow markings in the sidebar mean that the classes are imported but not used in the code, where normally, if I hadn't removed "ct.sym", I would have seen red error marking instead, and the code wouldn't have compiled. Note: I've tried setting "-XDignore.symbol.file" in "netbeans.conf" and in other places, but so far haven't got that to work. Simply deleting the "ct.sym" file (or back it up somewhere and put it back when needed) is quite clearly the most straightforward solution. Ultimately, if you want to be able to use those internal classes while still having portable code, do you know what you need to do? You need to create a JDK bug report stating that you need an internal class to be added to "ct.sym". Probably you'll get a motivation back stating WHY that internal class isn't supposed to be used externally. There must be a reason why those classes aren't available for external usage, otherwise they would have been added to "ct.sym". So, now the only remaining question is why the Eclipse compiler doesn't hide the internal JDK classes. Apparently the Eclipse compiler ignores the "ct.sym" file. In other words, at the end of the day, far from being a bug in NetBeans... we have now found a (pretty enormous, I reckon) bug in Eclipse. The Eclipse compiler does not protect you from using internal JDK classes and the code that you create in Eclipse may not work with future releases of the JDK, since the JDK team is simply going to be changing those classes that are not found in the "ct.sym" file while assuming (correctly, thanks to the presence of "ct.sym" mechanism) that no code in the world, other than JDK code, is tied to those classes.

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  • CruiseControl.NET: using $(CCNetLabel ) inside ccnet.config file

    - by minty
    When calling external processes like MSBuild cruise control sets environment variables. One of values is CCNetLabel. it holds the value of the current projects label. I want to use the same values in ccnet config itself but when I try ccnet config has a problem. I get the following error: [CCNet Server:ERROR] INTERNAL ERROR: Reference to unknown symbol CCNetLabel ---------- ThoughtWorks.CruiseControl.Core.Config.Preprocessor.EvaluationException: Reference to unknown symbol CCNetLabel at ThoughtWorks.CruiseControl.Core.Config.Preprocessor.ConfigPreprocessorEnvironment._GetConstantDef(String name) at ThoughtWorks.CruiseControl.Core.Config.Preprocessor.ConfigPreprocessorEnvironment.eval_text_constant(String name) ..... ---------- I actually want to append the CCNetLabel to another variable so I need to access the property in ccnet.config. is there a different way to reference these variables?

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  • windbg dv cmd fail - Private symbols (symbols.pri) are required for locals

    - by leif
    i have a C++ application compiled with VS 2008 with pdb file enabled. After i tried to use dv command to display local vars, it shows the following message: Unable to enumerate locals, HRESULT0x80004005 Private symbols (symbols.pri) are required for locals. Type ".hh dbgerr005" for details. Note that: i've run the "dv" command on the correct frame which has the symbol file. i can use "dt" command successfully. i've included the symbol path and the pdb file has been loaded successfully as following: start end module name 00400000 0043f000 helloworld (private pdb symbols) c:\test... Does anyone know the cause? Is there any configuration i missed to enable local var watch? Or VS 2008 pdb is not supported by windbg (i'm using the latest windbg version)?

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  • How do you read a segfault kernel log message.

    - by Sullenx
    This can be a very simple question, I'm am attempting to debug an application which generates the following segfault error in the kern.log /var/log/kern.log.0:Jan 8 13:25:56 myhost kernel: myapp[15514]: segfault at 794ef0 ip 080513b sp 794ef0 error 6 in myapp[8048000+24000] Here are my questions: 1) Is there any documentation as to what are the diff error numbers on segfault, in this instance it is error 6, but i've seen error 4, 5 2) What is the meaning of the information at bf794ef0 ip 0805130b sp bf794ef0 and myapp[8048000+24000]? So far i was able to compile with symbols, and when i do a "x 0x8048000+24000" it returns a symbol, is that the correct way of doing it? My assumptions thus far are the following: sp = stack pointer? ip = instruction pointer at = ???? myapp[8048000+24000] = address of symbol?

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