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• Computer Networks UNISA - Chap 8 &ndash; Wireless Networking

  - by MarkPearl

  After reading this section you should be able to Explain how nodes exchange wireless signals Identify potential obstacles to successful transmission and their repercussions, such as interference and reflection Understand WLAN architecture Specify the characteristics of popular WLAN transmission methods including 802.11 a/b/g/n Install and configure wireless access points and their clients Describe wireless MAN and WAN technologies, including 802.16 and satellite communications The Wireless Spectrum All wireless signals are carried through the air by electromagnetic waves. The wireless spectrum is a continuum of the electromagnetic waves used for data and voice communication. The wireless spectrum falls between 9KHZ and 300 GHZ. Characteristics of Wireless Transmission Antennas Each type of wireless service requires an antenna specifically designed for that service. The service’s specification determine the antenna’s power output, frequency, and radiation pattern. A directional antenna issues wireless signals along a single direction. An omnidirectional antenna issues and receives wireless signals with equal strength and clarity in all directions The geographical area that an antenna or wireless system can reach is known as its range Signal Propagation LOS (line of sight) uses the least amount of energy and results in the reception of the clearest possible signal. When there is an obstacle in the way, the signal may… pass through the object or be obsrobed by the object or may be subject to reflection, diffraction or scattering. Reflection – waves encounter an object and bounces off it. Diffraction – signal splits into secondary waves when it encounters an obstruction Scattering – is the diffusion or the reflection in multiple different directions of a signal Signal Degradation Fading occurs as a signal hits various objects. Because of fading, the strength of the signal that reaches the receiver is lower than the transmitted signal strength. The further a signal moves from its source, the weaker it gets (this is called attenuation) Signals are also affected by noise – the electromagnetic interference) Interference can distort and weaken a wireless signal in the same way that noise distorts and weakens a wired signal. Frequency Ranges Older wireless devices used the 2.4 GHZ band to send and receive signals. This had 11 communication channels that are unlicensed. Newer wireless devices can also use the 5 GHZ band which has 24 unlicensed bands Narrowband, Broadband, and Spread Spectrum Signals Narrowband – a transmitter concentrates the signal energy at a single frequency or in a very small range of frequencies Broadband – uses a relatively wide band of the wireless spectrum and offers higher throughputs than narrowband technologies The use of multiple frequencies to transmit a signal is known as spread-spectrum technology. In other words a signal never stays continuously within one frequency range during its transmission. One specific implementation of spread spectrum is FHSS (frequency hoping spread spectrum). Another type is known as DSS (direct sequence spread spectrum) Fixed vs. Mobile Each type of wireless communication falls into one of two categories Fixed – the location of the transmitted and receiver do not move (results in energy saved because weaker signal strength is possible with directional antennas) Mobile – the location can change WLAN (Wireless LAN) Architecture There are two main types of arrangements Adhoc – data is sent directly between devices – good for small local devices Infrastructure mode – a wireless access point is placed centrally, that all devices connect with 802.11 WLANs The most popular wireless standards used on contemporary LANs are those developed by IEEE’s 802.11 committee. Over the years several distinct standards related to wireless networking have been released. Four of the best known standards are also referred to as Wi-Fi. They are…. 802.11b 802.11a 802.11g 802.11n These four standards share many characteristics. i.e. All 4 use half duplex signalling Follow the same access method Access Method 802.11 standards specify the use of CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance) to access a shared medium. Using CSMA/CA before a station begins to send data on an 802.11 network, it checks for existing wireless transmissions. If the source node detects no transmission activity on the network, it waits a brief period of time and then sends its transmission. If the source does detect activity, it waits a brief period of time before checking again. The destination node receives the transmission and, after verifying its accuracy, issues an acknowledgement (ACT) packet to the source. If the source receives the ACK it assumes the transmission was successful, – if it does not receive an ACK it assumes the transmission failed and sends it again. Association Two types of scanning… Active – station transmits a special frame, known as a prove, on all available channels within its frequency range. When an access point finds the probe frame, it issues a probe response. Passive – wireless station listens on all channels within its frequency range for a special signal, known as a beacon frame, issued from an access point – the beacon frame contains information necessary to connect to the point. Re-association occurs when a mobile user moves out of one access point’s range and into the range of another. Frames Read page 378 – 381 about frames and specific 802.11 protocols Bluetooth Networks Sony Ericson originally invented the Bluetooth technology in the early 1990s. In 1998 other manufacturers joined Ericsson in the Special Interest Group (SIG) whose aim was to refine and standardize the technology. Bluetooth was designed to be used on small networks composed of personal communications devices. It has become popular wireless technology for communicating among cellular telephones, phone headsets, etc. Wireless WANs and Internet Access Refer to pages 396 – 402 of the textbook for details.

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• A Knights Tale

  - by Phil Factor

  There are so many lessons to be learned from the story of Knight Capital losing nearly half a billion dollars as a result of a deployment gone wrong. The Knight Capital Group (KCG N) was an American global financial services firm engaging in market making, electronic execution, and institutional sales and trading. According to the recent order (File No.3.15570) against Knight Capital by U.S. Securities and Exchange Commission?, Knight had, for many years used some software which broke up incoming “parent” orders into smaller “child” orders that were then transmitted to various exchanges or trading venues for execution. A tracking ‘cumulative quantity’ function counted the number of ‘child’ orders and stopped the process once the total of child orders matched the ‘parent’ and so the parent order had been completed. Back in the mists of time, some code had been added to it  which was excuted if a particular flag was set. It was called ‘power peg’ and seems to have had a similar design and purpose, but, one guesses, would have shared the same tracking function. This code had been abandoned in 2003, but never deleted. In 2005, The tracking function was moved to an earlier point in the main process. It would seem from the account that, from that point, had that flag ever been set, the old ‘Power Peg’ would have been executed like Godzilla bursting from the ice, making child orders without limit without any tracking function. It wasn’t, presumably because the software that set the flag was removed. In 2012, nearly a decade after ‘Power Peg’ was abandoned, Knight prepared a new module to their software to cope with the imminent Retail Liquidity Program (RLP) for the New York Stock Exchange. By this time, the flag had remained unused and someone made the fateful decision to reuse it, and replace the old ‘power peg’ code with this new RLP code. Had the two actions been done together in a single automated deployment, and the new deployment tested, all would have been well. It wasn’t. To quote… “Beginning on July 27, 2012, Knight deployed the new RLP code in SMARS in stages by placing it on a limited number of servers in SMARS on successive days. During the deployment of the new code, however, one of Knight’s technicians did not copy the new code to one of the eight SMARS computer servers. Knight did not have a second technician review this deployment and no one at Knight realized that the Power Peg code had not been removed from the eighth server, nor the new RLP code added. Knight had no written procedures that required such a review.” (para 15) “On August 1, Knight received orders from broker-dealers whose customers were eligible to participate in the RLP. The seven servers that received the new code processed these orders correctly. However, orders sent with the repurposed flag to the eighth server triggered the defective Power Peg code still present on that server. As a result, this server began sending child orders to certain trading centers for execution. Because the cumulative quantity function had been moved, this server continuously sent child orders, in rapid sequence, for each incoming parent order without regard to the number of share executions Knight had already received from trading centers. Although one part of Knight’s order handling system recognized that the parent orders had been filled, this information was not communicated to SMARS.” (para 16) SMARS routed millions of orders into the market over a 45-minute period, and obtained over 4 million executions in 154 stocks for more than 397 million shares. By the time that Knight stopped sending the orders, Knight had assumed a net long position in 80 stocks of approximately $3.5 billion and a net short position in 74 stocks of approximately $3.15 billion. Knight’s shares dropped more than 20% after traders saw extreme volume spikes in a number of stocks, including preferred shares of Wells Fargo (JWF) and semiconductor company Spansion (CODE). Both stocks, which see roughly 100,000 trade per day, had changed hands more than 4 million times by late morning. Ultimately, Knight lost over $460 million from this wild 45 minutes of trading. Obviously, I’m interested in all this because, at one time, I used to write trading systems for the City of London. Obviously, the US SEC is in a far better position than any of us to work out the failings of Knight’s IT department, and the report makes for painful reading. I can’t help observing, though, that even with the breathtaking mistakes all along the way, that a robust automated deployment process that was ‘all-or-nothing’, and tested from soup to nuts would have prevented the disaster. The report reads like a Greek Tragedy. All the way along one wants to shout ‘No! not that way!’ and ‘Aargh! Don’t do it!’. As the tragedy unfolds, the audience weeps for the players, trapped by a cruel fate. All application development and deployment requires defense in depth. All IT goes wrong occasionally, but if there is a culture of defensive programming throughout, the consequences are usually containable. For financial systems, these defenses are required by statute, and ignored only by the foolish. Knight’s mistakes weren’t made by just one hapless sysadmin, but were progressive errors by an  IT culture spanning at least ten years.  One can spell these out, but I think they’re obvious. One can only hope that the industry studies what happened in detail, learns from the mistakes, and draws the right conclusions.

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• Proxied calls not working as expected

  - by AndyH

  I have been modifying an application to have a cleaner client/server split to allow for load splitting and resource sharing etc. Everything is written to an interface so it was easy to add a remoting layer to the interface using a proxy. Everything worked fine. The next phase was to add a caching layer to the interface and again this worked fine and speed was improved but not as much as I would have expected. On inspection it became very clear what was going on. I feel sure that this behavior has been seen many times before and there is probably a design pattern to solve the problem but it eludes me and I'm not even sure how to describe it. It is easiest explained with an example. Let's imagine the interface is interface IMyCode { List<IThing> getLots( List<String> ); IThing getOne( String id ); } The getLots() method calls getOne() and fills up the list before returning. The interface is implemented at the client which is proxied to a remoting client which then calls the remoting server which in turn calls the implementation at the server. At the client and the server layers there is also a cache. So we have :- Client interface | Client cache | Remote client | Remote server | Server cache | Server interface If we call getOne("A") at the client interface, the call is passed to the client cache which faults. This then calls the remote client which passes the call to the remote server. This then calls the server cache which also faults and so the call is eventually passed to the server interface which actually gets the IThing. In turn the server cache is filled and finally the client cache also. If getOne("A") is again called at the client interface the client cache has the data and it gets returned immediately. If a second client called getOne("B") it would fill the server cache with "B" as well as it's own client cache. Then, when the first client calls getOne("B") the client cache faults but the server cache has the data. This is all as one would expect and works well. Now lets call getLots( [ "C", "D" ] ). This works as you would expect by calling getOne() twice but there is a subtlety here. The call to getLots() cannot directly make use of the cache. Therefore the sequence is to call the client interface which in turn calls the remote client, then the remote server and eventually the server interface. This then calls getOne() to fill the list before returning. The problem is that the getOne() calls are being satisfied at the server when ideally they should be satisfied at the client. If you imagine that the client/server link is really slow then it becomes clear why the client call is more efficient than the server call once the client cache has the data. This example is contrived to illustrate the point. The more general problem is that you cannot just keep adding proxied layers to an interface and expect it to work as you would imagine. As soon as the call goes 'through' the proxy any subsequent calls are on the proxied side rather than 'self' side. Have I failed to learn or not learned something correctly? All this is implemented in Java and I haven't used EJBs. It seems that the example may be confusing. The problem is nothing to do with cache efficiencies. It is more to do with an illusion created by the use of proxies or AOP techniques in general. When you have an object whose class implements an interface there is an assumption that a call on that object might make further calls on that same object. For example, public String getInternalString() { return InetAddress.getLocalHost().toString(); } public String getString() { return getInternalString(); } If you get an object and call getString() the result depends where the code is running. If you add a remoting proxy to the class then the result could be different for calls to getString() and getInternalString() on the same object. This is because the initial call gets 'deproxied' before the actual method is called. I find this not only confusing but I wonder how I can control this behavior especially as the use of the proxy may be by a third party. The concept is fine but the practice is certainly not what I expected. Have I missed the point somewhere?

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• Speed up executable program Linux. Bit Toggling

  - by AK_47

  I have a ZyBo circuit board which has a ArmV7 processor. I wrote a C program to output a clock and a corresponding data sequence on a PMOD. The PMOD has a switching speed of up to 50MHz. However, my program's created clock only has a max frequency of 115 Hz. I need this program to output as fast as possible because the PMOD I'm using is capable of 50MHz. I compiled my program with the following code line: gcc -ofast (c_program) Here is some sample code: #include <stdio.h> #include <stdlib.h> #define ARRAYSIZE 511 //________________________________________ //macro for the SIGNAL PMOD //________________________________________ //DATA //ZYBO Use Pin JE1 #define INIT_SIGNAL system("echo 54 > /sys/class/gpio/export"); system("echo out > /sys/class/gpio/gpio54/direction"); #define SIGNAL_ON system("echo 1 > /sys/class/gpio/gpio54/value"); #define SIGNAL_OFF system("echo 0 > /sys/class/gpio/gpio54/value"); //________________________________________ //macro for the "CLOCK" PMOD //________________________________________ //CLOCK //ZYBO Use Pin JE4 #define INIT_MYCLOCK system("echo 57 > /sys/class/gpio/export"); system("echo out > /sys/class/gpio/gpio57/direction"); #define MYCLOCK_ON system("echo 1 > /sys/class/gpio/gpio57/value"); #define MYCLOCK_OFF system("echo 0 > /sys/class/gpio/gpio57/value"); int main(void){ int myarray[ARRAYSIZE] = {//hard coded array for signal data 1,0,0,1,0,1,0,0,1,0,1,0,0,1,0,1,0,0,1,0,1,0,0,1,0,0,1,0,1,0,0,1,1,0,0,1,1,0,1,0,0,0,0,0,1,0,0,1,1,1,0,0,1,1,1,0,1,1,1,1,0,0,1,0,0,0,1,0,1,0,0,1,1,1,0,0,1,0,1,0,1,0,0,1,0,1,1,0,1,0,1,1,0,0,1,1,1,1,0,0,1,0,1,0,0,1,1,1,1,1,1,0,0,1,0,0,1,1,0,1,0,0,0,0,1,0,0,0,1,1,0,0,1,0,1,1,1,0,0,0,1,0,0,0,1,0,1,0,0,0,1,0,0,1,0,1,1,1,1,0,1,1,0,1,0,0,1,0,0,0,1,0,1,0,0,1,0,0,0,1,0,0,0,1,0,1,0,1,0,1,0,1,1,0,0,0,0,0,0,0,0,1,0,1,1,0,1,1,1,1,1,0,0,1,1,1,0,0,1,1,0,1,1,0,1,1,1,0,0,1,1,1,1,1,0,0,1,0,1,0,1,0,1,1,0,1,0,0,0,1,1,1,0,1,0,1,0,1,0,1,0,1,0,1,0,0,1,0,0,0,0,1,1,1,0,1,1,1,1,0,1,1,0,1,0,1,0,1,0,0,1,0,1,1,1,0,1,1,1,0,0,1,1,1,0,1,0,0,1,0,1,1,1,1,1,0,1,1,1,1,1,1,1,0,1,1,0,0,1,0,1,1,0,1,0,1,1,1,0,0,0,0,0,1,0,0,0,1,0,1,1,1,1,1,1,1,0,0,0,0,0,1,1,0,1,1,1,1,1,1,1,1,0,1,1,0,1,0,0,0,1,1,1,1,1,1,1,1,1,1,0,1,1,1,1,0,1,1,1,0,1,0,1,1,1,0,0,0,1,0,1,0,1,0,0,1,1,0,0,1,1,0,1,0,0,1,0,0,1,0,1,1,1,1,1,1,0,1,1,0,1,0,1,1,1,1,1,1,0,0,1,1,0,1,1,0,0,1,1,0,1,1,0,1,0,1,0,1,0,1,0,0,1,1,1,0,1,1,0,0,0,0,1,1,0,1,1,0,1,1,1,1,1,1,1,0,1,0,1,1,0,0,0,0,0,0,0,0,0,0,0 }; INIT_SIGNAL INIT_MYCLOCK; //infinite loop int i; do{ i = 0; do{ /* 1020 is chosen because it is twice the size needed allowing for the changes in the clock. (511= 0-510, 510*2= 1020 ==> 0-1020 needed, so 1021 it is) */ if((i%2)==0) { MYCLOCK_ON; if(myarray[i/2] == 1){ SIGNAL_ON; }else{ SIGNAL_OFF; } } else if((i%2)==1) { MYCLOCK_OFF; //dont need to change the signal since it will just stay at whatever it was. } ++i; } while(i < 1021); } while(1); return 0; } I'm using the 'system' call to tell the system to output 1 volt or 0 volts onto a pin on the board (to represent the data signal and clock signal. One pin for the data and another for the clock). That was the only way I knew to tell the system to output a voltage. What can I do to make my executable program output to be at least in the magnitude of MegaHertz?

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• Exiting a reboot loop

  - by user12617035

  If you're in a situation where the system is panic'ing during boot, you can use # boot net -s to regain control of your system. In my case, I'd added some diagnostic code to a (PCI) driver (that is used to boot the root filesystem). There was a bug in the driver, and each time during boot, the bug occurred, and so caused the system to panic: ... 000000000180b950 genunix:vfs_mountroot+60 (800, 200, 0, 185d400, 1883000, 18aec00) %l0-3: 0000000000001770 0000000000000640 0000000001814000 00000000000008fc %l4-7: 0000000001833c00 00000000018b1000 0000000000000600 0000000000000200 000000000180ba10 genunix:main+98 (18141a0, 1013800, 18362c0, 18ab800, 180e000, 1814000) %l0-3: 0000000070002000 0000000000000001 000000000180c000 000000000180e000 %l4-7: 0000000000000001 0000000001074800 0000000000000060 0000000000000000 skipping system dump - no dump device configured rebooting... If you're logged in via the console, you can send a BREAK sequence in order to gain control of the firmware's (OBP's) prompt. Enter Ctrl-Shift-[ in order to get the TELNET prompt. Once telnet has control, enter this: telnet> send brk You'll be presented with OBP's prompt: ok You then enter the following in order to boot into single-user mode via the network: ok boot net -s Note that booting from the network under Solaris will implicitly cause the system to be INSTALLED with whatever software had last been configured to be installed. However, we are using boot net -s as a "handle" with which to get at the Solaris prompt. Once at that prompt, we can perform actions as root that will let us back out our buggy driver (ok... MY buggy driver :-)) ...and replace it with the original, non-buggy driver. Entering the boot command caused the following output, as well as left us at the Solaris prompt (in single-user-mode): Sun Blade 1500, No Keyboard Copyright 1998-2004 Sun Microsystems, Inc. All rights reserved. OpenBoot 4.16.4, 1024 MB memory installed, Serial #53463393. Ethernet address 0:3:ba:2f:c9:61, Host ID: 832fc961. Rebooting with command: boot net -s Boot device: /pci@1f,700000/network@2 File and args: -s 1000 Mbps FDX Link up Timeout waiting for ARP/RARP packet Timeout waiting for ARP/RARP packet 4000 1000 Mbps FDX Link up Requesting Internet address for 0:3:ba:2f:c9:61 SunOS Release 5.10 Version Generic_118833-17 64-bit Copyright 1983-2005 Sun Microsystems, Inc. All rights reserved. Use is subject to license terms. Booting to milestone "milestone/single-user:default". Configuring devices. Using RPC Bootparams for network configuration information. Attempting to configure interface bge0... Configured interface bge0 Requesting System Maintenance Mode SINGLE USER MODE # Our goal is to now move to the directory containing the buggy driver and replace it with the original driver (that we had saved away before ever loading our buggy driver! :-) However, since we booted from the network, the root filesystem ("/") is NOT mounted on one of our local disks. It is mounted on an NFS filesystem exported by our install server. To verify this, enter the following command: # mount | head -1 / on my-server:/export/install/media/s10u2/solarisdvd.s10s_u2dvd/latest/Solaris_10/Tools/Boot remote/read/write/setuid/devices/dev=4ac0001 on Wed Dec 31 16:00:00 1969 As a result, we have to create a temporary mount point and then mount the local disk onto that mount point: # mkdir /tmp/mnt # mount /dev/dsk/c0t0d0s0 /tmp/mnt Note that your system will not necessarily have had its root filesystem on "c0t0d0s0". This is something that you should also have recorded before you ever loaded your.. er... "my" buggy driver! :-) One can find the local disk mounted under the root filesystem by entering: # df -k / Filesystem kbytes used avail capacity Mounted on /dev/dsk/c0t0d0s0 76703839 4035535 71901266 6% / To continue with our example, we can now move to the directory of buggy-driver in order to replace it with the original driver. Note that /tmp/mnt is prefixed to the path of where we'd "normally" find the driver: # cd /tmp/mnt/platform/sun4u/kernel/drv/sparcv9 # ls -l pci\* -rw-r--r-- 1 root root 288504 Dec 6 15:38 pcisch -rw-r--r-- 1 root root 288504 Dec 6 15:38 pcisch.aar -rwxr-xr-x 1 root sys 211616 Jun 8 2006 pcisch.orig # cp -p pcisch.orig pcisch We can now synchronize any in-memory filesystem data structures with those on disk... and then reboot. The system will then boot correctly... as expected: # sync;sync # reboot syncing file systems... done Sun Blade 1500, No Keyboard Copyright 1998-2004 Sun Microsystems, Inc. All rights reserved. OpenBoot 4.16.4, 1024 MB memory installed, Serial #xxxxxxxx. Ethernet address 0:3:ba:2f:c9:61, Host ID: yyyyyyyy. Rebooting with command: boot Boot device: /pci@1e,600000/ide@d/disk@0,0:a File and args: SunOS Release 5.10 Version Generic_118833-17 64-bit Copyright 1983-2005 Sun Microsystems, Inc. All rights reserved. Use is subject to license terms. Hostname: my-host NIS domain name is my-campus.Central.Sun.COM my-host console login: ...so that's how it's done! Of course, the easier way is to never write a buggy-driver... but.. then.. we all "have an eraser on the end of each of our pencils"... don't we ? :-) "...thank you... and good night..."

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• Plagued by multithreaded bugs

  - by koncurrency

  On my new team that I manage, the majority of our code is platform, TCP socket, and http networking code. All C++. Most of it originated from other developers that have left the team. The current developers on the team are very smart, but mostly junior in terms of experience. Our biggest problem: multi-threaded concurrency bugs. Most of our class libraries are written to be asynchronous by use of some thread pool classes. Methods on the class libraries often enqueue long running taks onto the thread pool from one thread and then the callback methods of that class get invoked on a different thread. As a result, we have a lot of edge case bugs involving incorrect threading assumptions. This results in subtle bugs that go beyond just having critical sections and locks to guard against concurrency issues. What makes these problems even harder is that the attempts to fix are often incorrect. Some mistakes I've observed the team attempting (or within the legacy code itself) includes something like the following: Common mistake #1 - Fixing concurrency issue by just put a lock around the shared data, but forgetting about what happens when methods don't get called in an expected order. Here's a very simple example: void Foo::OnHttpRequestComplete(statuscode status) { m_pBar->DoSomethingImportant(status); } void Foo::Shutdown() { m_pBar->Cleanup(); delete m_pBar; m_pBar=nullptr; } So now we have a bug in which Shutdown could get called while OnHttpNetworkRequestComplete is occuring on. A tester finds the bug, captures the crash dump, and assigns the bug to a developer. He in turn fixes the bug like this. void Foo::OnHttpRequestComplete(statuscode status) { AutoLock lock(m_cs); m_pBar->DoSomethingImportant(status); } void Foo::Shutdown() { AutoLock lock(m_cs); m_pBar->Cleanup(); delete m_pBar; m_pBar=nullptr; } The above fix looks good until you realize there's an even more subtle edge case. What happens if Shutdown gets called before OnHttpRequestComplete gets called back? The real world examples my team has are even more complex, and the edge cases are even harder to spot during the code review process. Common Mistake #2 - fixing deadlock issues by blindly exiting the lock, wait for the other thread to finish, then re-enter the lock - but without handling the case that the object just got updated by the other thread! Common Mistake #3 - Even though the objects are reference counted, the shutdown sequence "releases" it's pointer. But forgets to wait for the thread that is still running to release it's instance. As such, components are shutdown cleanly, then spurious or late callbacks are invoked on an object in an state not expecting any more calls. There are other edge cases, but the bottom line is this: Multithreaded programming is just plain hard, even for smart people. As I catch these mistakes, I spend time discussing the errors with each developer on developing a more appropriate fix. But I suspect they are often confused on how to solve each issue because of the enormous amount of legacy code that the "right" fix will involve touching. We're going to be shipping soon, and I'm sure the patches we're applying will hold for the upcoming release. Afterwards, we're going to have some time to improve the code base and refactor where needed. We won't have time to just re-write everything. And the majority of the code isn't all that bad. But I'm looking to refactor code such that threading issues can be avoided altogether. One approach I am considering is this. For each significant platform feature, have a dedicated single thread where all events and network callbacks get marshalled onto. Similar to COM apartment threading in Windows with use of a message loop. Long blocking operations could still get dispatched to a work pool thread, but the completion callback is invoked on on the component's thread. Components could possibly even share the same thread. Then all the class libraries running inside the thread can be written under the assumption of a single threaded world. Before I go down that path, I am also very interested if there are other standard techniques or design patterns for dealing with multithreaded issues. And I have to emphasize - something beyond a book that describes the basics of mutexes and semaphores. What do you think? I am also interested in any other approaches to take towards a refactoring process. Including any of the following: Literature or papers on design patterns around threads. Something beyond an introduction to mutexes and semaphores. We don't need massive parallelism either, just ways to design an object model so as to handle asynchronous events from other threads correctly. Ways to diagram the threading of various components, so that it will be easy to study and evolve solutions for. (That is, a UML equivalent for discussing threads across objects and classes) Educating your development team on the issues with multithreaded code. What would you do?

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• Tips / techniques for high-performance C# server sockets

  - by McKenzieG1

  I have a .NET 2.0 server that seems to be running into scaling problems, probably due to poor design of the socket-handling code, and I am looking for guidance on how I might redesign it to improve performance. Usage scenario: 50 - 150 clients, high rate (up to 100s / second) of small messages (10s of bytes each) to / from each client. Client connections are long-lived - typically hours. (The server is part of a trading system. The client messages are aggregated into groups to send to an exchange over a smaller number of 'outbound' socket connections, and acknowledgment messages are sent back to the clients as each group is processed by the exchange.) OS is Windows Server 2003, hardware is 2 x 4-core X5355. Current client socket design: A TcpListener spawns a thread to read each client socket as clients connect. The threads block on Socket.Receive, parsing incoming messages and inserting them into a set of queues for processing by the core server logic. Acknowledgment messages are sent back out over the client sockets using async Socket.BeginSend calls from the threads that talk to the exchange side. Observed problems: As the client count has grown (now 60-70), we have started to see intermittent delays of up to 100s of milliseconds while sending and receiving data to/from the clients. (We log timestamps for each acknowledgment message, and we can see occasional long gaps in the timestamp sequence for bunches of acks from the same group that normally go out in a few ms total.) Overall system CPU usage is low (< 10%), there is plenty of free RAM, and the core logic and the outbound (exchange-facing) side are performing fine, so the problem seems to be isolated to the client-facing socket code. There is ample network bandwidth between the server and clients (gigabit LAN), and we have ruled out network or hardware-layer problems. Any suggestions or pointers to useful resources would be greatly appreciated. If anyone has any diagnostic or debugging tips for figuring out exactly what is going wrong, those would be great as well. Note: I have the MSDN Magazine article Winsock: Get Closer to the Wire with High-Performance Sockets in .NET, and I have glanced at the Kodart "XF.Server" component - it looks sketchy at best.

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• UML assignment question

  - by waitinforatrain

  Hi guys, Sorry, I know this is a very lame question to ask and not of any use to anyone else. I have an assignment in UML due tomorrow and I don't even know the basics (all-nighter ahead!). I'm not looking for a walkthrough, I simply want your opinion on something. The assignment is as follows (you only need to skim over it!): ============= Gourmet Surprise (GS) is a small catering firm with five employees. During a typical weekend, GS caters fifteen events with twenty to fifty people each. The business has grown rapidly over the past year and the owner wants to install a new computer system for managing the ordering and buying process. GS has a set of ten standard menus. When potential customers call, the receptionist describes the menus to them. If the customer decides to book an event (dinner, lunch, picnic, finger food etc.), the receptionist records the customer information (e.g., name, address, phone number, etc.) and the information about the event (e.g., place, date, time, which one of the standard menus, total price) on a contract. The customer is then faxed a copy of the contract and must sign and return it along with a deposit (often a credit card or by check) before the event is officially booked. The remaining money is collected when the catering is delivered. Sometimes, the customer wants something special (e.g., birthday cake). In this case, the receptionist takes the information and gives it to the owner who determines the cost; the receptionist then calls the customer back with the price information. Sometimes the customer accepts the price, other times, the customer requests some changes that have to go back to the owner for a new cost estimate. Each week, the owner looks through the events scheduled for that weekend and orders the supplies (e.g., plates) and food (e.g., bread, chicken) needed to make them. The owner would like to use the system for marketing as well. It should be able to track how customers learned about GS, and identify repeat customers, so that GS can mail special offers to them. The owner also wants to track the events on which GS sent a contract, but the customer never signed the contract and actually booked a GS. Exercise: Create an activity diagram and a use case model (complete with a set of detail use case descriptions) for the above system. Produce an initial domain model (class diagram) based on these descriptions. Elaborate the use cases into sequence diagrams, and include any state diagrams necessary. Finally use the information from these dynamic models to expand the domain model into a full application model. ============= In your opinion, do you think this question is asking me to come up with a package for an online ordering system to replace the system described above, or to create UML diagrams that facilitate the existing telephone-based system?

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• How do you get Matlab to write the BOM (byte order markers) for UTF-16 text files?

  - by Richard Povinelli

  I am creating UTF16 text files with Matlab, which I am later reading in using Java. In Matlab, I open a file called fileName and write to it as follows: fid = fopen(fileName, 'w','n','UTF16-LE'); fprintf(fid,"Some stuff."); In Java, I can read the text file using the following code: FileInputStream fileInputStream = new FileInputStream(fileName); Scanner scanner = new Scanner(fileInputStream, "UTF-16LE"); String s = scanner.nextLine(); Here is the hex output: Offset(h) 00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F 10 11 12 13 00000000 73 00 6F 00 6D 00 65 00 20 00 73 00 74 00 75 00 66 00 66 00 s.o.m.e. .s.t.u.f.f. The above approach works fine. But, I want to be able to write out the file using UTF16 with a BOM to give me more flexibility so that I don't have to worry about big or little endian. In Matlab, I've coded: fid = fopen(fileName, 'w','n','UTF16'); fprintf(fid,"Some stuff."); In Java, I change the code to: FileInputStream fileInputStream = new FileInputStream(fileName); Scanner scanner = new Scanner(fileInputStream, "UTF-16"); String s = scanner.nextLine(); In this case, the string s is garbled, because Matlab is not writing the BOM. I can get the Java code to work just fine if I add the BOM manually. With the added BOM, the following file works fine. Offset(h) 00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F 10 11 12 13 14 15 00000000 FF FE 73 00 6F 00 6D 00 65 00 20 00 73 00 74 00 75 00 66 00 66 00 ÿþs.o.m.e. .s.t.u.f.f. How can I get Matlab to write out the BOM? I know I could write the BOM out separately, but I'd rather have Matlab do it automatically. Addendum I selected the answer below from Amro because it exactly solves the question I posed. One key discovery for me was the difference between the Unicode Standard and a UTF (Unicode transformation format) (see http://unicode.org/faq/utf_bom.html). The Unicode Standard provides unique identifiers (code points) for characters. UTFs provide mappings of every code point "to a unique byte sequence." Since all but a handful of the characters I am using are in the first 128 code points, I'm going to switch to using UTF-8 as Romeo suggests. UTF-8 is supported by Matlab (The warning shown below won't need to be suppressed.) and Java, and for my application will generate smaller text files. I suppress the Matlab warning Warning: The encoding 'UTF-16LE' is not supported. with warning off MATLAB:iofun:UnsupportedEncoding;

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• Sharepoint 2007 - cant find my modifications to web.config in SpWebApplication.WebConfigModification

  - by user303672

  Hi, I cant seem to find the modifications I made to web.config in my FeatureRecievers Activated event. I try to get the modifications from the SpWebApplication.WebConfigModifications collection in the deactivate event, but this is always empty.... And the strangest thing is that my changes are still reverted after deactivating the feature... My question is, should I not be able to view all changes made to the web.config files when accessing the SpWebApplication.WebConfigModifications collection in the Deactivating event? How should I go about to remove my changes explicitly? public class FeatureReciever : SPFeatureReceiver { private const string FEATURE_NAME = "HelloWorld"; private class Modification { public string Name; public string XPath; public string Value; public SPWebConfigModification.SPWebConfigModificationType ModificationType; public bool createOnly; public Modification(string name, string xPath, string value, SPWebConfigModification.SPWebConfigModificationType modificationType, bool createOnly) { Name = name; XPath = xPath; Value = value; ModificationType = modificationType; this.createOnly = createOnly; } } private Modification[] modifications = { new Modification("connectionStrings", "configuration", "<connectionStrings/>", SPWebConfigModification.SPWebConfigModificationType.EnsureChildNode, true), new Modification("add[@name='ConnectionString'][@connectionString='Data Source=serverName;Initial Catalog=DBName;User Id=UserId;Password=Pass']", "configuration/connectionStrings", "<add name='ConnectionString' connectionString='Data Source=serverName;Initial Catalog=DBName;User Id=UserId;Password=Pass'/>", SPWebConfigModification.SPWebConfigModificationType.EnsureChildNode, false) }; public override void FeatureActivated(SPFeatureReceiverProperties properties) { SPSite siteCollection = (properties.Feature.Parent as SPWeb).Site as SPSite; SPWebApplication webApplication = siteCollection.WebApplication; siteCollection.RootWeb.Title = "Set from activating code at " + DateTime.Now.ToString(); foreach (Modification entry in modifications) { SPWebConfigModification webConfigModification = CreateModification(entry); webApplication.WebConfigModifications.Add(webConfigModification); } webApplication.Farm.Services.GetValue<SPWebService>().ApplyWebConfigModifications(); webApplication.WebService.Update(); } public override void FeatureDeactivating(SPFeatureReceiverProperties properties) { SPSite siteCollection = (properties.Feature.Parent as SPWeb).Site as SPSite; SPWebApplication webApplication = siteCollection.WebApplication; siteCollection.RootWeb.Title = "Set from deactivating code at " + DateTime.Now.ToString(); IList<SPWebConfigModification> modifications = webApplication.WebConfigModifications; foreach (SPWebConfigModification modification in modifications) { if (modification.Owner == FEATURE_NAME) { webApplication.WebConfigModifications.Remove(modification); } } webApplication.Farm.Services.GetValue<SPWebService>().ApplyWebConfigModifications(); webApplication.WebService.Update(); } public override void FeatureInstalled(SPFeatureReceiverProperties properties) { } public override void FeatureUninstalling(SPFeatureReceiverProperties properties) { } private SPWebConfigModification CreateModification(Modification entry) { SPWebConfigModification spWebConfigModification = new SPWebConfigModification() { Name = entry.Name, Path = entry.XPath, Owner = FEATURE_NAME, Sequence = 0, Type = entry.ModificationType, Value = entry.Value }; return spWebConfigModification; } } Thanks for your time. /Hans

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• gwt-RPC problem! what is the best practice on using gwt-RPC?

  - by guaz

  Dear all, I want draw a chart based on the date retrieve from the database by using RPC. But everytime I fail to get the result. My rpc function is working. I think is the sequence of the process. below is my class: public class TrafficPattern_1 extends GChart { TrafficPattern_1() { final DBServiceAsync dbService = GWT .create(DBService.class); dbService.SendData(null, null, new AsyncCallback<Container_TrafficPattern>() { @Override public void onFailure(Throwable caught) { } @Override public void onSuccess(Container_TrafficPattern result) { // TODO Auto-generated method stub pContainer.SetaDate(result.aDate.get(1)); } }); pContainer.aDate.get(0); setChartSize(350, 200); setChartTitle("<h2>Temperature vs Time<h2>"); setPadding("8px"); //setPixelSize(380, 200); getXAxis().setAxisLabel("<small><b><i>Time</i></b></small>"); getXAxis().setHasGridlines(true); getXAxis().setTickCount(6); // Except for "=(Date)", a standard GWT DateTimeFormat string getXAxis().setTickLabelFormat("=(Date)h:mm a"); getYAxis().setAxisLabel("<small><b><i>&deg;C</i></b></small>"); getYAxis().setHasGridlines(true); getYAxis().setTickCount(11); getYAxis().setAxisMin(11); getYAxis().setAxisMax(16); addCurve(); getCurve().setLegendLabel("<i> </i>"); getCurve().getSymbol().setBorderColor("blue"); getCurve().getSymbol().setBackgroundColor("blue"); // getCurve().getSymbol().setFillSpacing(10); // getCurve().getSymbol().setFillThickness(3); getCurve().getSymbol().setSymbolType(SymbolType.LINE); getCurve().getSymbol().setFillThickness(2); getCurve().getSymbol().setFillSpacing(1); for (int i = 0; i < dateSequence.length; i++) // Note that getTime() returns milliseconds since // 1/1/70--required whenever "date cast" tick label // formats (those beginning with "=(Date)") are used. getCurve().addPoint(dateSequence[i].date.getTime(), dateSequence[i].value); }

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• Attempting to extract a pattern within a string

  - by Brian

  I'm attempting to extract a given pattern within a text file, however, the results are not 100% what I want. Here's my code: import java.util.regex.Matcher; import java.util.regex.Pattern; public class ParseText1 { public static void main(String[] args) { String content = "<p>Yada yada yada <code> foo ddd</code>yada yada ...\n" + "more here <2004-08-24> bar<Bob Joe> etc etc\n" + "more here again <2004-09-24> bar<Bob Joe> <Fred Kej> etc etc\n" + "more here again <2004-08-24> bar<Bob Joe><Fred Kej> etc etc\n" + "and still more <2004-08-21><2004-08-21> baz <John Doe> and now <code>the end</code> </p>\n"; Pattern p = Pattern .compile("<[1234567890]{4}-[1234567890]{2}-[1234567890]{2}>.*?<[^%0-9/]*>", Pattern.MULTILINE); Matcher m = p.matcher(content); // print all the matches that we find while (m.find()) { System.out.println(m.group()); } } } The output I'm getting is: <2004-08-24> bar<Bob Joe> <2004-09-24> bar<Bob Joe> <Fred Kej> <2004-08-24> bar<Bob Joe><Fred Kej> <2004-08-21><2004-08-21> baz <John Doe> and now <code> The output I want is: <2004-08-24> bar<Bob Joe> <2004-08-24> bar<Bob Joe> <2004-08-24> bar<Bob Joe> <2004-08-21> baz <John Doe> In short, the sequence of "date", "text (or blank)", and "name" must be extracted. Everything else should be avoided. For example the tag "Fred Kej" did not have any "date" tag before it, therefore, it should be flagged as invalid. Also, as a side question, is there a way to store or track the text snippets that were skipped/rejected as were the valid texts. Thanks, Brian

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• Problem: adding feature in MOSS 2007

  - by Anoop

  Hi All, I have added a menu item in 'Actions' menu of a document library as follows(Using features: explained in MSDN How to: Add Actions to the User Interface: http://msdn.microsoft.com/en-us/library/ms473643.aspx): feature.xml as follows: <?xml version="1.0" encoding="utf-8" ?> <Feature Id="51DEF381-F853-4991-B8DC-EBFB485BACDA" Title="Import From REP" Description="This example shows how you can customize various areas inside Windows SharePoint Services." Version="1.0.0.0" Scope="Site" xmlns="http://schemas.microsoft.com/sharepoint/"> <ElementManifests> <ElementManifest Location="ImportFromREP.xml" /> </ElementManifests> </Feature> ImportFromREP.xml is as follows: <?xml version="1.0" encoding="utf-8"?> <Elements xmlns="http://schemas.microsoft.com/sharepoint/"> <!-- Document Library Toolbar Actions Menu Dropdown --> <CustomAction Id="ImportFromREP" RegistrationType="List" RegistrationId = "101" GroupId="ActionsMenu" Rights="AddListItems" Location="Microsoft.SharePoint.StandardMenu" Sequence="1000" Title="Import From REP"> <UrlAction Url="/_layouts/ImportFromREP.aspx?ActionsMenu"/> </CustomAction> </Elements> I have successfully installed and activated the feature. Normal case: Now if i login with the user having atleast 'Contribute' permission on the document library, i am able to see the menu item 'Import From REP' (in 'Actions' menu)in root folder as well as in all subfolders. Problem case: If user is having view rights on the document library but add/delete rights on a perticular subfolder(say 'subfolder') inside the document library: Menu item 'Import From REP' is not visible on root folder level as well as 'Upload' menu is also not visible. which is o.k. because user does not have AddListItems right on root folder but it is also not visible in 'subfolder' while 'Upload' menu is visible as user has add/delete rights on the 'subfolder'. did i mention a wrong value of attribute Rights(Rights="AddListItems") in the xml file?? If so, what should be the correct value? What should i do to simulate the behaviour of 'Upload' menu??(i.e. when 'Upload' menu is visible, 'Import From REP' menu is visible and when 'Upload' menu is not visible 'Import From REP' menu is also not visible. ) Thanks in advance Anoop

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• ASP.NET Web Service Throws 401 (unauthorized) Error

  - by user268611

  Hi Experts, I have this .NET application to be run in an intranet environment. It is configured so that it requires Windows Authentication before you can access the website (Anonymous access is disabled). This website calls a web service (enable anonymous access) and the web service calls the DB. We do have a token-based authentication between the web application and the web service to secure the communication between them. The issue I'm facing is that when I deploy this to production, I'm having an intermittent issue whereby the communication between the web application and the web service failed. The 401 issue was thrown. This is actually working fine in our QA environment. Is this an issue with Active Directory? Or could it be an isssue with FQDN as mentioned here: http://support.microsoft.com/default.aspx?scid=kb;en-us;896861? The weirdest thing is that this is happening intermittently when tested in both on the server itself and a remote workstation in my client's environment. But, this is working perfectly in my environment. OS: Windows Server SP1 IIS 6 .NET 3.5 Framework Any idea about the 401 (Unauthorized) issue?? Thx for the help... This is from the log... Event code: 3005 Event message: An unhandled exception has occurred. Event time: 4/5/2010 10:44:57 AM Event time (UTC): 4/5/2010 2:44:57 AM Event ID: 6c8ea2607b8d4e29a7f0b1c392b1cb21 Event sequence: 155112 Event occurrence: 2 Event detail code: 0 Application information: Application domain: xxx Trust level: Full Application Virtual Path: xxx Application Path: xxx Machine name: xxx Process information: Process ID: 4424 Process name: w3wp.exe Account name: NT AUTHORITY\NETWORK SERVICE Exception information: Exception type: WebException Exception message: The request failed with HTTP status 401: Unauthorized. Request information: Request URL: http://[ip]/[app_path] Request path: xxx User host address: [ip] User: xxx Is authenticated: True Authentication Type: Negotiate Thread account name: xxx Thread information: Thread ID: 6 Thread account name: xxx Is impersonating: False Stack trace: at System.Web.Services.Protocols.SoapHttpClientProtocol.ReadResponse(SoapClientMessage message, WebResponse response, Stream responseStream, Boolean asyncCall) at System.Web.Services.Protocols.SoapHttpClientProtocol.Invoke(String methodName, Object[] parameters) at wsVulnerabilityAdvisory.Service.test() at test.Page_Load(Object sender, EventArgs e) at System.Web.Util.CalliHelper.EventArgFunctionCaller(IntPtr fp, Object o, Object t, EventArgs e) at System.Web.Util.CalliEventHandlerDelegateProxy.Callback(Object sender, EventArgs e) at System.Web.UI.Control.OnLoad(EventArgs e) at System.Web.UI.Control.LoadRecursive() at System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint)

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• Problem with waveOutWrite and waveOutGetPosition deadlock

  - by MusiGenesis

  I'm working on an app that plays audio continuously using the waveOut... API from winmm.dll. The app uses "leapfrog" buffers, which are basically a bunch of arrays of samples that you dump into the audio queue. Windows plays them seamlessly in sequence, and as each buffer completes Windows calls a callback function. Inside this function, I load the next set of samples into the buffer, process them however, and then dump the buffer back into the audio queue. In this way, the audio plays indefinitely. For animation purposes, I'm trying to incorporate waveOutGetPosition into the application (since the "buffer done" callbacks are irregular enough to cause jerky animation). waveOutGetPosition returns the current position of playback, so it's hyper-precise. The problem is that in my application, making calls to waveOutGetPosition eventually causes the application to lock up - the sound stops and the call never returns. I've boiled things down to a simple app that demonstrates the problem. You can run the app here: http://www.musigenesis.com/SO/waveOut%20demo.exe If you just hear a tiny bit of piano over and over, it's working. It's just meant to demonstrate the problem. The source code for this project is here: http://www.musigenesis.com/SO/WaveOutDemo.zip The first button runs the app in leapfrog mode without making the calls to waveOutGetPosition. If you click this, the app will play forever without breaking (the X button will close it and shut it off). The second button starts the leapfrogger and also starts a forms timer that calls the waveOutGetPosition and displays the current position. Click this and the app will run for a short while and then lock up. On my laptop, it usually locks up in 15-30 seconds; at most it's taken a minute. I have no idea how to fix this, so any help or suggestions would be most welcome. I've found very few posts on this issue, but it seems that there is a potential deadlock, either from multiple calls to waveOutGetPosition or from calls to that and waveOutWrite that occur at the same time. It's possible that I'm calling this too frequently for the system to handle.

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• Best practice to handle Parent Form Child Form relation using Presentation Model

  - by Rajarshi

  According to Presentation Model notes by Martin Fowler and also on MSDN documentation about Presentation Model, it is explained that the Presentation Model Class should be unaware of the UI class and similarly Business Model Class should be unaware of the Presentation Model class. The UI should databind extensively to the Presentation Model, the Presentation Model in turn will co-ordinate with one or more Domain/Business Model objects to get the job done. The Presentation Model basically presents the Domain Model data in a way to facilitate maximum data binding in UI, allowing the UI take as less decisions as possible and thus increase testability of Presentation behaviours. This also makes the presentation model class generic, i.e. agnostic of any particular UI technology. Now, consider there is a List form (say CustomerList) and there is another Root form (say Customer) and there is a Use Case of allowing to Edit a Customer from the CustomerList form on a button click. For simplicity of discussion, consider that some actions took place when Customer List is opened from menu (i.e. Customer menu clicked) and the Customer List has been shown from the Menu click event. Now as per the above Use Case, I need to open the Customer Root UI (single Customer) from the Customer List. How do I do that? Build necessary objects (BusinessModel, PresentationModel, UI) in click event of Edit button and call CustomerEdit UI from there? Build the CustomerEdit UI from Presentation Model Class and show UI from presentation model? this can be done in any of the two ways below - a. Create objects in the following sequence DomainModel-PresentationModel-UIForm b. Use Unity.Resolve(); Either ways, Presentation Model is violated as the P model now has to the refer the concrete UI assembly, where CustomerEdit is located. Also the P Model has to refer and use a WinForm directly making it less UI technology agnostic. Even though the violations are in theory and can be ignored, I would still seek the community's opinion about whether I am going wrong direction. Please suggest if there's a better way to call the Child Form from the List (Parent) Form. Rajarshi

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• The Skyline Problem.

  - by zeroDivisible

  I just came across this little problem on UVA's Online Judge and thought, that it may be a good candidate for a little code-golf. The problem: You are to design a program to assist an architect in drawing the skyline of a city given the locations of the buildings in the city. To make the problem tractable, all buildings are rectangular in shape and they share a common bottom (the city they are built in is very flat). The city is also viewed as two-dimensional. A building is specified by an ordered triple (Li, Hi, Ri) where Li and Ri are left and right coordinates, respectively, of building i and Hi is the height of the building. In the diagram below buildings are shown on the left with triples (1,11,5), (2,6,7), (3,13,9), (12,7,16), (14,3,25), (19,18,22), (23,13,29), (24,4,28) and the skyline, shown on the right, is represented by the sequence: 1, 11, 3, 13, 9, 0, 12, 7, 16, 3, 19, 18, 22, 3, 23, 13, 29, 0 The output should consist of the vector that describes the skyline as shown in the example above. In the skyline vector (v1, v2, v3, ... vn) , the vi such that i is an even number represent a horizontal line (height). The vi such that i is an odd number represent a vertical line (x-coordinate). The skyline vector should represent the "path" taken, for example, by a bug starting at the minimum x-coordinate and traveling horizontally and vertically over all the lines that define the skyline. Thus the last entry in the skyline vector will be a 0. The coordinates must be separated by a blank space. If I will not count declaration of provided (test) buildings and including all spaces and tab characters, my solution, in Python, is 223 characters long. Here is the condensed version: B=[[1,11,5],[2,6,7],[3,13,9],[12,7,16],[14,3,25],[19,18,22],[23,13,29],[24,4,28]] # Solution. R=range v=[0 for e in R(max([y[2] for y in B])+1)] for b in B: for x in R(b[0], b[2]): if b[1]>v[x]: v[x]=b[1] p=1 k=0 for x in R(len(v)): V=v[x] if p and V==0: continue elif V!=k: p=0 print "%s %s" % (str(x), str(V)), k=V I think that I didn't made any mistake but if so - feel free to criticize me. EDIT I don't have much reputation, so I will pay only 100 for a bounty - I am curious, if anyone could try to solve this in less than .. lets say, 80 characters. Solution posted by cobbal is 101 characters long and currently it is the best one. ANOTHER EDIT I thought, that 80 characters is a sick limit for this kind of problem. cobbal, with his 46 character solution totaly amazed me - though I must admit, that I spent some time reading his explanation before I partially understood what he had written.

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• spoj: runlength

  - by user285825

  For RLM problem of SPOJ: This is the problem: "Run-length encoding of a number replaces a run of digits (that is, a sequence of consecutive equivalent digits) with the number of digits followed by the digit itself. For example, 44455 would become 3425 (three fours, two fives). Note that run-length encoding does not necessarily shorten the length of the data: 11 becomes 21, and 42 becomes 1412. If a number has more than nine consecutive digits of the same type, the encoding is done greedily: each run grabs as many digits as it can, so 111111111111111 is encoded as 9161. Implement an integer arithmetic calculator that takes operands and gives results in run-length format. You should support addition, subtraction, multiplication, and division. You won't have to divide by zero or deal with negative numbers. Input/Output The input will consist of several test cases, one per line. For each test case, compute the run-length mathematics expression and output the original expression and the result, as shown in the examples. The (decimal) representation of all operands and results will fit in signed 64-bit integers." These are my testcases: input: 11 + 11 988726 - 978625 12 * 41 1124 / 1112 13 * 33 15 / 16 19222317121013161815142715181017 + 10 10 + 19222317121013161815142715181017 19222317121013161815142715181017 / 19222317121013161815142715181017 19222317121013161815142715181017 / 11 11 / 19222317121013161815142715181017 19222317121013161815142715181017 / 12 12 / 19222317121013161815142715181017 19222317121013161815142715181017 / 141621161816101118141217131817191014 141621161816101118141217131817191014 / 19222317121013161815142715181017 19222317121013161815142715181017 / 141621161816101118141217131817191013 141621161816101118141217131817191013 / 19222317121013161815142715181017 19222317121013161815142715181017 * 11 11 * 19222317121013161815142715181017 19222317121013161815142715181017 * 10 10 * 19222317121013161815142715181017 19222317121013161815142715181017 - 10 19222317121013161815142715181017 - 19222317121013161815142715181017 19222317121013161815142715181017 - 141621161816101118141217131817191014 19222317121013161815142715181017 - 141621161816101118141217131817191013 141621161816101118141217131817191013 + 141621161816101118141217131817191013 141621161816101118141217131817191013 + 141621161816101118141217131817191014 141621161816101118141217131817191014 + 141621161816101118141217131817191013 141621161816101118141217131817191014 + 10 10 + 141621161816101118141217131817191013 141621161816101118141217131817191013 + 11 11 + 141621161816101118141217131817191013 141621161816101118141217131817191013 * 12 12 * 141621161816101118141217131817191013 141621161816101118141217131817191014 - 141621161816101118141217131817191014 141621161816101118141217131817191013 - 141621161816101118141217131817191013 141621161816101118141217131817191013 - 10 141621161816101118141217131817191014 - 11 141621161816101118141217131817191014 - 141621161816101118141217131817191013 141621161816101118141217131817191014 / 141621161816101118141217131817191014 141621161816101118141217131817191014 / 141621161816101118141217131817191013 141621161816101118141217131817191013 / 141621161816101118141217131817191014 141621161816101118141217131817191013 / 141621161816101118141217131817191013 141621161816101118141217131817191014 * 11 11 * 141621161816101118141217131817191014 141621161816101118141217131817191014 / 11 11 / 141621161816101118141217131817191014 10 + 10 10 + 11 10 + 15 15 + 10 11 + 10 11 + 10 10 - 10 15 - 10 10 * 10 10 * 15 15 * 10 10 / 111213 output: 11 + 11 = 12 988726 - 978625 = 919111 12 * 41 = 42 1124 / 1112 = 1112 13 * 33 = 39 15 / 16 = 10 19222317121013161815142715181017 + 10 = 19222317121013161815142715181017 10 + 19222317121013161815142715181017 = 19222317121013161815142715181017 19222317121013161815142715181017 / 19222317121013161815142715181017 = 11 19222317121013161815142715181017 / 11 = 19222317121013161815142715181017 11 / 19222317121013161815142715181017 = 10 19222317121013161815142715181017 / 12 = 141621161816101118141217131817191013 12 / 19222317121013161815142715181017 = 10 19222317121013161815142715181017 / 141621161816101118141217131817191014 = 11 141621161816101118141217131817191014 / 19222317121013161815142715181017 = 10 19222317121013161815142715181017 / 141621161816101118141217131817191013 = 12 141621161816101118141217131817191013 / 19222317121013161815142715181017 = 10 19222317121013161815142715181017 * 11 = 19222317121013161815142715181017 11 * 19222317121013161815142715181017 = 19222317121013161815142715181017 19222317121013161815142715181017 * 10 = 10 10 * 19222317121013161815142715181017 = 10 19222317121013161815142715181017 - 10 = 19222317121013161815142715181017 19222317121013161815142715181017 - 19222317121013161815142715181017 = 10 19222317121013161815142715181017 - 141621161816101118141217131817191014 = 141621161816101118141217131817191013 19222317121013161815142715181017 - 141621161816101118141217131817191013 = 141621161816101118141217131817191014 141621161816101118141217131817191013 + 141621161816101118141217131817191013 = 19222317121013161815142715181016 141621161816101118141217131817191013 + 141621161816101118141217131817191014 = 19222317121013161815142715181017 141621161816101118141217131817191014 + 141621161816101118141217131817191013 = 19222317121013161815142715181017 141621161816101118141217131817191014 + 10 = 141621161816101118141217131817191014 10 + 141621161816101118141217131817191013 = 141621161816101118141217131817191013 141621161816101118141217131817191013 + 11 = 141621161816101118141217131817191014 11 + 141621161816101118141217131817191013 = 141621161816101118141217131817191014 141621161816101118141217131817191013 * 12 = 19222317121013161815142715181016 12 * 141621161816101118141217131817191013 = 19222317121013161815142715181016 141621161816101118141217131817191014 - 141621161816101118141217131817191014 = 10 141621161816101118141217131817191013 - 141621161816101118141217131817191013 = 10 141621161816101118141217131817191013 - 10 = 141621161816101118141217131817191013 141621161816101118141217131817191014 - 11 = 141621161816101118141217131817191013 141621161816101118141217131817191014 - 141621161816101118141217131817191013 = 11 141621161816101118141217131817191014 / 141621161816101118141217131817191014 = 11 141621161816101118141217131817191014 / 141621161816101118141217131817191013 = 11 141621161816101118141217131817191013 / 141621161816101118141217131817191014 = 10 141621161816101118141217131817191013 / 141621161816101118141217131817191013 = 11 141621161816101118141217131817191014 * 11 = 141621161816101118141217131817191014 11 * 141621161816101118141217131817191014 = 141621161816101118141217131817191014 141621161816101118141217131817191014 / 11 = 141621161816101118141217131817191014 11 / 141621161816101118141217131817191014 = 10 10 + 10 = 10 10 + 11 = 11 10 + 15 = 15 15 + 10 = 15 11 + 10 = 11 11 + 10 = 11 10 - 10 = 10 15 - 10 = 15 10 * 10 = 10 10 * 15 = 10 15 * 10 = 10 10 / 111213 = 10 I am getting consistently wrong answer. I generated the above testcases trying to make them as representative as possible (boundary conditions, etc). I am not sure how to test it further. Some guidline would be really appreciated.

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• Jquery Cycle Plugin Question - turning off relative links to photos so it goes to a URL

  - by alpdog14

  I am using Jquery Cycle Plugin and it has a side panel that highlights as the photos change and currently when I click on the text the associated photo pulls up then I have to click on the photo to go to the URL but I would like the text itself to link to the URL. I have looked at the fn.cycle.defaults but not sure what to change and I tried a few things but nothing works. If anyone can help me figure this out it would be most helpful. Here are the fn.cycle.defaults: fx: 'fade', // one of: fade, shuffle, zoom, scrollLeft, etc timeout: 4000, // milliseconds between slide transitions (0 to disable auto advance) continuous: 0, // true to start next transition immediately after current one completes speed: 1000, // speed of the transition (any valid fx speed value) speedIn: null, // speed of the 'in' transition speedOut: null, // speed of the 'out' transition next: null, // id of element to use as click trigger for next slide prev: null, // id of element to use as click trigger for previous slide prevNextClick: null, // callback fn for prev/next clicks: function(isNext, zeroBasedSlideIndex, slideElement) pager: null, // id of element to use as pager container pagerClick: null, // callback fn for pager clicks: function(zeroBasedSlideIndex, slideElement) pagerEvent: null, // event which drives the pager navigation pagerAnchorBuilder: null, // callback fn for building anchor links before: null, // transition callback (scope set to element to be shown) after: null, // transition callback (scope set to element that was shown) end: null, // callback invoked when the slideshow terminates (use with autostop or nowrap options) easing: null, // easing method for both in and out transitions easeIn: null, // easing for "in" transition easeOut: null, // easing for "out" transition shuffle: null, // coords for shuffle animation, ex: { top:15, left: 200 } animIn: null, // properties that define how the slide animates in animOut: null, // properties that define how the slide animates out cssBefore: null, // properties that define the initial state of the slide before transitioning in cssAfter: null, // properties that defined the state of the slide after transitioning out fxFn: null, // function used to control the transition height: 'auto', // container height startingSlide: 0, // zero-based index of the first slide to be displayed sync: 1, // true if in/out transitions should occur simultaneously random: 0, // true for random, false for sequence (not applicable to shuffle fx) fit: 0, // force slides to fit container pause: true, // true to enable "pause on hover" autostop: 0, // true to end slideshow after X transitions (where X == slide count) autostopCount: 0, // number of transitions (optionally used with autostop to define X) delay: 0, // additional delay (in ms) for first transition (hint: can be negative) slideExpr: null, // expression for selecting slides (if something other than all children is required) cleartype: 0, // true if clearType corrections should be applied (for IE) nowrap: 0 // true to prevent slideshow from wrapping }; I have tried changing the pageClick and pagerEvent but nothing seems to be working. Please help!!!

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• Need help receiving ByteArray data

  - by k80sg

  Hi folks, I am trying to receive byte array data from a machine. It sends out 3 different types of data structure each with different number of fields which consist of mostly int and a few floats, and byte sizes, the first being 320 bytes, 420 for the second type and 560 for the third. When the sending program is launched, it fires all 3 types of data simultaneouly with an interval of 1 sec. Example: Sending order: Pack1 - 320 bytes 1 sec later Pack2 - 420 bytes 1 sec later Pack3 - 560 bytes 1 sec later Pack1 - 320 bytes ... .. . How do I check the incoming byte size before passing it to: byte[] handsize = new byte[bytesize]; as the data I receive are all out of order, for instance using the following the read all int: System.out.println("Reading data in int format:" + " " + datainput.readInt()); I get many different sets of values whenever I run my prog although with some valid field data but they are all over the place. I am not too sure how exactly should I do it but I tried the following and apparently my data fields are not receiving in correct sequence: BufferedInputStream bais = new BufferedInputStream(requestSocket.getInputStream()); DataInputStream datainput = new DataInputStream(bais); byte[] handsize = new byte[560]; datainput.readFully(handsize); int n = 0; int intByte[] = new int[140]; for (int i = 0; i < 140 ; i++) { System.out.println("Reading data in int format:" + " " + datainput.readInt()); intByte[n] = datainput.readInt(); n = n + 1; System.out.println("The value in array is:" + intByte[0]); System.out.println("The value in array is:" + intByte[1]); System.out.println("The value in array is:" + intByte[2]); System.out.println("The value in array is:" + intByte[3]); Also from the above code, the order of the values printed out with System.out.println("Reading data in int format:" + " " + datainput.readInt()); and System.out.println("The value in array is:" + intByte[0]); System.out.println("The value in array is:" + intByte[1]); are different. Any help will be appreciated. Thanks

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• Most efficient algorithm for merging sorted IEnumerable<T>

  - by franck

  Hello, I have several huge sorted enumerable sequences that I want to merge. Theses lists are manipulated as IEnumerable but are already sorted. Since input lists are sorted, it should be possible to merge them in one trip, without re-sorting anything. I would like to keep the defered execution behavior. I tried to write a naive algorithm which do that (see below). However, it looks pretty ugly and I'm sure it can be optimized. It may exist a more academical algorithm... IEnumerable<T> MergeOrderedLists<T, TOrder>(IEnumerable<IEnumerable<T>> orderedlists, Func<T, TOrder> orderBy) { var enumerators = orderedlists.ToDictionary(l => l.GetEnumerator(), l => default(T)); IEnumerator<T> tag = null; var firstRun = true; while (true) { var toRemove = new List<IEnumerator<T>>(); var toAdd = new List<KeyValuePair<IEnumerator<T>, T>>(); foreach (var pair in enumerators.Where(pair => firstRun || tag == pair.Key)) { if (pair.Key.MoveNext()) toAdd.Add(pair); else toRemove.Add(pair.Key); } foreach (var enumerator in toRemove) enumerators.Remove(enumerator); foreach (var pair in toAdd) enumerators[pair.Key] = pair.Key.Current; if (enumerators.Count == 0) yield break; var min = enumerators.OrderBy(t => orderBy(t.Value)).FirstOrDefault(); tag = min.Key; yield return min.Value; firstRun = false; } } The method can be used like that: // Person lists are already sorted by age MergeOrderedLists(orderedList, p => p.Age); assuming the following Person class exists somewhere: public class Person { public int Age { get; set; } } Duplicates should be conserved, we don't care about their order in the new sequence. Do you see any obvious optimization I could use?

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• How to make the selected testcript is run in selenium grid

  - by Yui

  Hi, I can launch some remote control by using: ant launch-remote-control but I dont know how my script connect to hub? I set up ant, selenium-grid on the same computer. I have an grid.dll which is written by C# and run through NUnit. The test data is read from xml file (ValidData.xml) The example code is below : using System.Collections.Generic; using System.Linq; using System.Text; using System; using System.Xml; using System.Text.RegularExpressions; using System.Threading; using NUnit.Framework; using Selenium; namespace Grid { public class Class1 { //User defined private string strURL = "http://gmail.com/"; private string[] strBrowser = new string[3] { "*iehta", "*firefox", "*safari" }; string hubAddress = "192.168.20.131"; // IP of my computer // System defined private ISelenium selenium; private StringBuilder verificationErrors; [SetUp] public void SetupTest() { selenium = new DefaultSelenium(hubAddress, 4444, this.strBrowser[1], this.strURL);// do i need to identify browser when I defined it when launching a remote control selenium.Start(); verificationErrors = new StringBuilder(); } [TearDown] public void TeardownTest() { try { selenium.Stop(); } catch (Exception) { // Ignore errors if unable to close the browser } Assert.AreEqual("", verificationErrors.ToString()); } private string[] name; [Test] public void LoginPassedTest() { try { XmlDocument doc = new XmlDocument(); XmlNode docNode; doc.Load("ValidData.xml"); docNode = doc["TestCase"]; foreach (XmlNode node in docNode) { selenium.Open("/"); selenium.WaitForPageToLoad("50000"); selenium.Type("Email", node["username"].InnerText); selenium.Type("Passwd", node["password"].InnerText); selenium.Click("signIn"); selenium.WaitForPageToLoad("100000"); name = (selenium.GetText("//div[@id='guser']/nobr/b").Split('@')); try { Assert.AreEqual(node["username"].InnerText, name[0]); Assert.AreEqual("Sign out", selenium.GetText(":r6")); } catch (AssertionException e) { verificationErrors.Append(e.Message); } selenium.Click(":r6"); } } catch (AssertionException e) { verificationErrors.Append(e.Message); } } } } Step I run this script: 1.I build that script into DLL 2.I start hub by using command "ant lauch-hub" 3.I start 2 remote controls by using command : ant -Dport=5566 -Denvironment="*chrome" launch-remote-control ant -Dport=5577 -Denvironment="*iexplore" launch-remote-control 4.Then I open Nunit and load DLL (code above) and run 5.The NUNit doesnot respond anything. I think there are some missing things but I dont know. How can the test script (DLL) know which is sequence of remote control is selected to run the test???? Please help me!! Thank you so much Yui.

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• WIX Installing an EXE after Msi install finishes.

  - by Chris

  Hi, I have created an MSI package which when finishes runs an exe. <Package InstallerVersion="200" Compressed="yes" /> <Media Id="1" Cabinet="media1.cab" EmbedCab="yes" /> <Directory Id="TARGETDIR" Name="SourceDir"> <Directory Id="ProgramFilesFolder"> <Directory Id="INSTALLLOCATION" Name="Installer Example"> <Component Id="VSTOR30.EXE" Guid="4fb0aee7-ec5b-4179-8938-a2be4df8ca0e"> <File Id="VSTOR30.EXE" Source="C:\Projects\InstallationTarget\ExampleInstaller\VSTOR30.EXE" KeyPath="yes" Checksum="yes" /> </Component> </Directory> </Directory> </Directory> <Feature Id="ProductFeature" Title="Installation Target" Level="1"> <ComponentRef Id="VSTOR30.EXE" /> </Feature> <InstallExecuteSequence> <Custom Action="RunEXE" After="InstallFinalize">NOT Installed</Custom> </InstallExecuteSequence> <CustomAction Id="RunEXE" FileKey="VSTOR30.EXE" ExeCommand="[#VSTOR30.EXE]" Execute="immediate" Return="asyncNoWait"> </CustomAction> <UI /> The MSI installs but the EXE is not run. I am calling it after Install Finalize and checking the install sequence in ORCA shows that it is being called at the correct time. I need deploy this through group policy software installation which uses a silent install without inputs. If i use a custom UI and run the EXE in the exit dialog <UI> <UIRef Id="WixUI_Minimal" /> <Publish Dialog="ExitDialog" Control="Finish" Event="DoAction" Value="LaunchApplication">WIXUI_EXITDIALOGOPTIONALCHECKBOX = 1 and NOT Installed</Publish> </UI> <Property Id="WIXUI_EXITDIALOGOPTIONALCHECKBOXTEXT" Value="RunEXE" /> <!-- Step 3: Include the custom action --> <Property Id="WixShellExecTarget" Value="[#VSTOR30.exe]" /> <CustomAction Id="RunEXE" BinaryKey="WixCA" DllEntry="WixShellExec" Impersonate="yes" /> Then i can install the software after the msi has finished running, however when putting this group policy the EXE doesn't install. Is there anything i am missing? Chris

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• What was your the most impressive technical programming achievement performed to impress a romantic

  - by DVK

  OK, so the archetypal human story is for a guy to go out and impress the girl with some wonderful achievement like slaying a dragon or building a monument or conquering neighboring tribe. This being enlightened 21st century on SO, let's morph this into a: StackOverflower performing a feat of programming to impress a romantic interest. There are two ways to do this: Technical achievement: Impressing a person with suitable background/understanding of programming with actual coding powerss you displayed. A dumb movie example would be that kid in "Hackers" move showing off his hacking skills in front of Angeline Jolie. Artistic achievement: Impressing a person with a result of running said code, whether they understand just how incredible the code itself is. An example is the animated ANSI rose (for a guy who actually wrote the ANSI code) This question is only about the first kind (technical achievements) - e.g. the person of interest was presented with impressive code/design that (s)he was able to properly appreciate. Rules (what doesn't qualify): The target audience must have been a person of romantic interest (prospective or present significant other or random hook-up). E.g. showing your program to your sister who's also a software developer doesn't count. The achievement must have been done specifically with the goal to impress such a person. However, it is OK if the achievement was done to impress a generic qualifying person, not someone specific. Although... if you write code to impress girls in general, I'd say "get a better idea of the opposite sex" The achievement must have been done with the goal of impressing the person. In other words, if you would have done it without romantic interest's knowledge anyway, it doesn't count. As examples, the following does not count: programming for your job. Programming for a coding contest. Open Source program that you'd have done anyway. The precise nature of the awesomeness of the achievement is somewhat irrelevant - from learning entire J2EE in 2 days to writing fancy game engine to implementing Python compiler in LOGO. As long as it's programming/software development related. The achievement should preferably be something other people would rank highly as well. If your date was impressed with your skill at calculating Fibonacci sequence without recursive function calls, it doesn't mean most developers will be. But it does mean you need to start finding better things to do on dates ;)

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• Tomcat JNDI Connection Pool docs - Random Connection Closed Exceptions

  - by Andy Faibishenko

  I found this in the Tomcat documentation here What I don't understand is why they close all the JDBC objects twice - once in the try{} block and once in the finally{} block. Why not just close them once in the finally{} clause? This is the relevant docs: Random Connection Closed Exceptions These can occur when one request gets a db connection from the connection pool and closes it twice. When using a connection pool, closing the connection just returns it to the pool for reuse by another request, it doesn't close the connection. And Tomcat uses multiple threads to handle concurrent requests. Here is an example of the sequence of events which could cause this error in Tomcat: Request 1 running in Thread 1 gets a db connection. Request 1 closes the db connection. The JVM switches the running thread to Thread 2 Request 2 running in Thread 2 gets a db connection (the same db connection just closed by Request 1). The JVM switches the running thread back to Thread 1 Request 1 closes the db connection a second time in a finally block. The JVM switches the running thread back to Thread 2 Request 2 Thread 2 tries to use the db connection but fails because Request 1 closed it. Here is an example of properly written code to use a db connection obtained from a connection pool: Connection conn = null; Statement stmt = null; // Or PreparedStatement if needed ResultSet rs = null; try { conn = ... get connection from connection pool ... stmt = conn.createStatement("select ..."); rs = stmt.executeQuery(); ... iterate through the result set ... rs.close(); rs = null; stmt.close(); stmt = null; conn.close(); // Return to connection pool conn = null; // Make sure we don't close it twice } catch (SQLException e) { ... deal with errors ... } finally { // Always make sure result sets and statements are closed, // and the connection is returned to the pool if (rs != null) { try { rs.close(); } catch (SQLException e) { ; } rs = null; } if (stmt != null) { try { stmt.close(); } catch (SQLException e) { ; } stmt = null; } if (conn != null) { try { conn.close(); } catch (SQLException e) { ; } conn = null; } }

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