Search Results

Search found 10 results on 1 pages for 'taco'.

facebook twitter digg google delicious technorati stumbleupon myspace wordpress linkedin gmail igoogle windows live tumblr viadeo yahoo buzz yahoo mail yahoo bookmarks favorites email print

Page 1/1 | 1 

  • iCloud stuff stops working while connected to OpenVPN [closed]

    - by Taco Bob
    I have a fairly simple OpenVPN setup on an OpenVZ VPS with Ubuntu 11.10. Client is the Viscosity client on Mac OS X 10.8.2, and after some testing, we can rule out the client as being part of the problem. Everything has been working fine except for Apple's iCloud stuff. Web surfing, email, FTP, NNTP, and Skype are all working as expected. It's ONLY the iCloud services that cease to function. If I connect to the VPN, iCloud stuff stops working. I no longer get anything in Messages, Calendar items don't get updated, and Notifications stop working. If I disconnect, the iCloud stuff all starts working. Connect again, iCloud stops working. Here's the server.conf: status openvpn-status.log log /var/log/openvpn.log verb 4 port 1194 proto udp dev tun ca /etc/openvpn/ca.crt cert /etc/openvpn/server.crt key /etc/openvpn/server.key dh /etc/openvpn/dh1024.pem server 10.9.8.0 255.255.255.0 ifconfig-pool-persist ipp.txt push "redirect-gateway def1" push “dhcp-option DNS 10.9.8.1? keepalive 10 120 duplicate-cn cipher BF-CBC comp-lzo user nobody group nogroup persist-key persist-tun tun-mtu 1500 mssfix 1400 I'm using iptables in a script, and it's also fairly simplistic. iptables -F iptables -t nat -F iptables -t mangle -F iptables -A FORWARD -i tun0 -o venet0 -j ACCEPT iptables -A FORWARD -i venet0 -o tun0 -j ACCEPT iptables -A INPUT -p tcp --dport 22 -j ACCEPT iptables -A INPUT -p tcp --dport 1194 -j ACCEPT iptables -A INPUT -p udp --dport 1194 -j ACCEPT iptables -t nat -A POSTROUTING -s 10.9.8.0/24 -j SNAT --to-source <server's public ip> echo 1 > /proc/sys/net/ipv4/ip_forward I tried forwarding ports as well, with no success. iptables -A FORWARD -p tcp -d 10.9.8.0/24 --dport 5222:5230 -j ACCEPT iptables -t nat -A PREROUTING -p tcp --dport 5222:5230 -j DNAT --to-destination 10.9.8.6 I am also sometimes behind a double-NAT situation that I have no control over. Client -> work VPN -> my OpenVPN box -> Internet. Client -> Airport Express -> ISP (which is doing NAT) -> my OpenVPN box -> Internet. Those two situations are just the fact of life where I am, and I cannot change them. I do have full control over my client and the OpenVPN server. I am completely out of ideas. I have posted a similar query at the OpenVPN forums, but it hasn't posted yet and seems to be in their moderation queue still. Tried on freenode irc channels, but nobody is awake, so here I am. I have Googled extensively for this, and can find nothing that is related. Help me get iCloud stuff working again!

    Read the article

  • iCloud stuff stops working while connected to OpenVPN

    - by Taco Bob
    I have a fairly simple OpenVPN setup on an OpenVZ VPS with Ubuntu 11.10. Client is the Viscosity client on Mac OS X 10.8.2, and after some testing, we can rule out the client as being part of the problem. Everything has been working fine except for Apple's iCloud stuff. Web surfing, email, FTP, NNTP, and Skype are all working as expected. It's ONLY the iCloud services that cease to function. If I connect to the VPN, iCloud stuff stops working. I no longer get anything in Messages, Calendar items don't get updated, and Notifications stop working. If I disconnect, the iCloud stuff all starts working. Connect again, iCloud stops working. Here's the server.conf: status openvpn-status.log log /var/log/openvpn.log verb 4 port 1194 proto udp dev tun ca /etc/openvpn/ca.crt cert /etc/openvpn/server.crt key /etc/openvpn/server.key dh /etc/openvpn/dh1024.pem server 10.9.8.0 255.255.255.0 ifconfig-pool-persist ipp.txt push "redirect-gateway def1" push “dhcp-option DNS 10.9.8.1? keepalive 10 120 duplicate-cn cipher BF-CBC comp-lzo user nobody group nogroup persist-key persist-tun tun-mtu 1500 mssfix 1400 I'm using iptables in a script, and it's also fairly simplistic. iptables -F iptables -t nat -F iptables -t mangle -F iptables -A FORWARD -i tun0 -o venet0 -j ACCEPT iptables -A FORWARD -i venet0 -o tun0 -j ACCEPT iptables -A INPUT -p tcp --dport 22 -j ACCEPT iptables -A INPUT -p tcp --dport 1194 -j ACCEPT iptables -A INPUT -p udp --dport 1194 -j ACCEPT iptables -t nat -A POSTROUTING -s 10.9.8.0/24 -j SNAT --to-source <server's public ip> echo 1 > /proc/sys/net/ipv4/ip_forward I tried forwarding ports as well, with no success. iptables -A FORWARD -p tcp -d 10.9.8.0/24 --dport 5222:5230 -j ACCEPT iptables -t nat -A PREROUTING -p tcp --dport 5222:5230 -j DNAT --to-destination 10.9.8.6 I am also sometimes behind a double-NAT situation that I have no control over. Client -> work VPN -> my OpenVPN box -> Internet. Client -> Airport Express -> ISP (which is doing NAT) -> my OpenVPN box -> Internet. Those two situations are just the fact of life where I am, and I cannot change them. I do have full control over my client and the OpenVPN server. I am completely out of ideas. I have posted a similar query at the OpenVPN forums, but it hasn't posted yet and seems to be in their moderation queue still. Tried on freenode irc channels, but nobody is awake, so here I am. I have Googled extensively for this, and can find nothing that is related. Help me get iCloud stuff working again! (I tried serverfault, it was closed as off-topic. I'm trying here and the Unix site as well. Here because it's a more general audience that might know more about OpenVPN based on the number of questions I see asked about it) EDIT: -I have also tried upgrading to Version: 2.3-beta1-debian0 - issue persists. -Removed all iptables rules except for the ones that flush -left this rule:iptables -t nat -A POSTROUTING -s 10.9.8.0/24 -j SNAT --to-source (server ip) -added iptables -A FORWARD -m state --state RELATED,ESTABLISHED -j ACCEPT still, nothing works. I can see traffic in tcpdump on the server if i watch the tunnel: 20:03:48.702835 IP nk11p01st-courier105-bz.push.apple.com.5223 10.9.8.6.60772: Flags [F.], seq 2635, ack 1218, win 76, options [nop,nop,TS val 914984811 ecr 745921298], length 0 20:03:48.911244 IP 10.9.8.6.60772 nk11p01st-courier105-bz.push.apple.com.5223: Flags [R], seq 3621143451, win 0, length 0 But still, no push messages/notifications are ever delivered. :/ EDIT: * Further testing indicates that it might actually be the client after all.

    Read the article

  • What *collaborative* wireframing / UI mockup tools are out there?

    - by taco
    I'm looking for something that applies the collaboration focus (one location/URL, always up-to-date, multi-person online read/write access anywhere) of google docs / google spreadsheets to wireframing. Bonus points if, like Google Docs, it needs only a browser yet also works offline. More bonus points if it supports automatic revisions. Even more bonus points if you can hand out login-less 'invitation' URLs like Flickr does, instead of forcing people into signing up for accounts or using their home accounts. To start off, there's one called iPlotz, but it didn't enchant me -- ironically, mostly because of its akward UI, which can't hold a candle to omnigraffle (don't let that prevent you from giving it a try though). And no, paper prototyping, wonderful as it is, does not qualify: it does not combine being instantly globally shareable & editable very well :-)

    Read the article

  • Finding matches between multiple JavaScript Arrays

    - by Chris Barr
    I have multiple arrays with string values and I want to compare them and only keep the matching results that are identical between ALL of them. Given this example code: var arr1 = ['apple', 'orange', 'banana', 'pear', 'fish', 'pancake', 'taco', 'pizza']; var arr2 = ['taco', 'fish', 'apple', 'pizza']; var arr3 = ['banana', 'pizza', 'fish', 'apple']; I would like to to produce the following array that contains matches from all given arrays: ['apple', 'fish', 'pizza'] I know I can combine all the arrays with var newArr = arr1.concat(arr2, arr3); but that just give me an array with everything, plus the duplicates. Can this be done easily without needing the overhead of libraries such as underscore.js? (Great, and now i'm hungry too!) EDIT I suppose I should mention that there could be an unknown amount of arrays, I was just using 3 as an example.

    Read the article

  • Reduce weight in healthy way - Day 3

    - by krnites
    So I am on Day 3 and what I did today was totally opposite of what I should have done. It seems I will take ever to loose what I had aim for. Today I had ate more than 5000 Calorie, had soda drinks and very oily indian food. On my Day 2 post some one commented that with the number that I have I will loose 1 lbs in a week, but my friends it seems I will gain 5 lbs in a week. I have to straighten my act and really focus on what I want to achieve. I am going to hit the gym and going to burn atleast 500 calorie today.Piece of advice - don't eat fried, oily  and junk food.  Try to have as much as vegetables in your food. I understand its not possible as being a normal person and not a diet freak I know its impossible to be away from Taco or burger and not drink Coke, but to achieve something you have to loose something.

    Read the article

  • Facebook Stories for Retailers

    - by David Dorf
    Getting people to "like" a brand is important because it opens the door to a possible B2C relationship. Once a person likes that brand, the brand can post to their newsfeed with promotions, announcements, and surveys. At least for me, I "hide" the noisy brands and just monitor the ones that keep posts under 4 times a week. I see lots of people, especially with fashion brands, comment on postings at which point the posting is seen by their network. A metric I've heard (but not verified) is that for every person that comments, ten of their friends see the original posting. That's a pretty cheap way to communicate to potential customers in a viral way. Over at mainstreet.com they compiled the a list of the top liked retailers on Facebook as of Feb 1, 2011. They are listed below: 19,414,892 Starbucks 11,302,939 Victoria's Secret 7,925,184 Zara 7,032,398 McDonald's 6,117,222 H&M 5,400,586 Taco Bell 4,665,760 Subway 4,494,849 Lacoste 4,185,570 Hollister 3,973,181 Forever 21 So I guess the public likes their fast-food and fashion. To take this to the next level, Facebook is now displaying Sponsored Stories, which I saw for the first time on my page this weekend. I found this picture at the Wall Blog that depicits Sponsored Stories very well. Over on the right-hand column of a person's page, where they see advertisements and such, Facebook will post stories involving their network of friends and their interaction with sponsored brands. Now their "likes" can suddenly become your ads. "Jessica and Philip like Starbucks. What are you waiting for?" This is another great way to take messages viral by accessing social graphs. As usual there will be a certain level of outcry from privacy advocates, but given the other more iniquitous issues, I believe this will fall by the wayside. Retailers should consider using Sponsored Stories to increase their Likes, and thus increase their voice in the social world.

    Read the article

  • A programmer who doesn't get to program - where to turn? [closed]

    - by Just an Anon
    I'm in my mid 20's, and have been working as a full time programmer / developer for the last ~6 years, with several years of part-time freelancing before this, and three straight years of freelancing in the middle of this short career. I work mostly with PHP and the Drupal framework. By and large, I focus on programming custom pieces of functionality; these, of course, vary greatly from project to project. I've got years of solid experience with OOP (have done some Java & C# years ago, too) including intensive experience with front-end development, and even some design work. I've lead small teams (2-4 people) of developers. And of course, given the large amount of freelancing, I've got decent project- & client-management skills. My problem is staying motivated at any place of employment. In the time mentioned I've worked (full-time) at six local companies. The longest I've stayed at any company was just over a year. I find that I'll get hired and be very excited and motivated for the first few months, but the work quickly gets "stale." By that I mean that the interesting components (ie. the programming) get done, and the rest of the work turns into boring cleanup (move a button, add text, change colours, add a field). I don't get challenged, and I don't feel like I'm learning anything new. This happens repeatedly time and time again, and I always end up leaving for either a new opportunity, or to freelance. I'm wondering if perhaps I've painted myself into a corner with the rather niche work market (although with very high demand and good compensation) and need to explore other career choices. Another possibility is that I may be choosing the wrong places of employment, mostly small agencies, and need to look into working for a larger, more established firm. I find programming, writing code, and architecting solutions very rewarding. When I'm working on an interesting problem I lose all sense of time and 14-16 hours can fly by like minutes. I get the same exciting feeling when I'm doing high-level planning of a complex system, breaking up the work and figuring out how everything will tie-in together. I absolutely hate doing small, "stupid" changes that pose no challenge, yet seem to make up more and more of my work. I want to find a workplace where I will get to work on such tasks, be challenged, and improve in all areas of product development. This maybe a programming job, management, architecture of desktop apps, or may be managing a taco stand on a beach in Mexico - I don't know, and I need some advice and real-world feedback. What are some job areas worth exploring? The requirements are fairly simple: working with computers interacting with others challenging decent pay (I'm making just short of 90k / year with a month of vacation & some benefits, and would like to stay in this range, but am willing to take a temporary cut in pay for a more interesting position) Any advice would be much appreciated!

    Read the article

  • Pseudo random numbers in php

    - by pg
    I have a function that outputs items in a different order depending on a random number. for example 1/2 of the time Popeye's and its will be #1 on the list and Taco Bell and its logo will be #2 and half the time the it will be the other way around. The problem is that when a user reloads or comes back to the page, the order is re-randomized. $Range here is the number of items in the db, so it's using a random number between 1 and the $range. $random = mt_rand(1,$range); for ($i = 0 ; $i < count($variants); $i++) { $random -= $variants[$i]['weight']; if ($random <= 0) { $chosenoffers[$tag] = $variants[$i]; break; } } I went to the beginning of the session and set this: if (!isset($_SESSION['rannum'])){ $_SESSION['rannum']=rand(1,100); } With the idea that I could replace the mt_rand in the function with some sort of pseudo random generator that used the same 1-100 random number as a seed throughout the session. That way i won't have to rewrite all the code that was already written. Am I barking up the wrong tree or is this a good idea?

    Read the article

  • PTLQueue : a scalable bounded-capacity MPMC queue

    - by Dave
    Title: Fast concurrent MPMC queue -- I've used the following concurrent queue algorithm enough that it warrants a blog entry. I'll sketch out the design of a fast and scalable multiple-producer multiple-consumer (MPSC) concurrent queue called PTLQueue. The queue has bounded capacity and is implemented via a circular array. Bounded capacity can be a useful property if there's a mismatch between producer rates and consumer rates where an unbounded queue might otherwise result in excessive memory consumption by virtue of the container nodes that -- in some queue implementations -- are used to hold values. A bounded-capacity queue can provide flow control between components. Beware, however, that bounded collections can also result in resource deadlock if abused. The put() and take() operators are partial and wait for the collection to become non-full or non-empty, respectively. Put() and take() do not allocate memory, and are not vulnerable to the ABA pathologies. The PTLQueue algorithm can be implemented equally well in C/C++ and Java. Partial operators are often more convenient than total methods. In many use cases if the preconditions aren't met, there's nothing else useful the thread can do, so it may as well wait via a partial method. An exception is in the case of work-stealing queues where a thief might scan a set of queues from which it could potentially steal. Total methods return ASAP with a success-failure indication. (It's tempting to describe a queue or API as blocking or non-blocking instead of partial or total, but non-blocking is already an overloaded concurrency term. Perhaps waiting/non-waiting or patient/impatient might be better terms). It's also trivial to construct partial operators by busy-waiting via total operators, but such constructs may be less efficient than an operator explicitly and intentionally designed to wait. A PTLQueue instance contains an array of slots, where each slot has volatile Turn and MailBox fields. The array has power-of-two length allowing mod/div operations to be replaced by masking. We assume sensible padding and alignment to reduce the impact of false sharing. (On x86 I recommend 128-byte alignment and padding because of the adjacent-sector prefetch facility). Each queue also has PutCursor and TakeCursor cursor variables, each of which should be sequestered as the sole occupant of a cache line or sector. You can opt to use 64-bit integers if concerned about wrap-around aliasing in the cursor variables. Put(null) is considered illegal, but the caller or implementation can easily check for and convert null to a distinguished non-null proxy value if null happens to be a value you'd like to pass. Take() will accordingly convert the proxy value back to null. An advantage of PTLQueue is that you can use atomic fetch-and-increment for the partial methods. We initialize each slot at index I with (Turn=I, MailBox=null). Both cursors are initially 0. All shared variables are considered "volatile" and atomics such as CAS and AtomicFetchAndIncrement are presumed to have bidirectional fence semantics. Finally T is the templated type. I've sketched out a total tryTake() method below that allows the caller to poll the queue. tryPut() has an analogous construction. Zebra stripping : alternating row colors for nice-looking code listings. See also google code "prettify" : https://code.google.com/p/google-code-prettify/ Prettify is a javascript module that yields the HTML/CSS/JS equivalent of pretty-print. -- pre:nth-child(odd) { background-color:#ff0000; } pre:nth-child(even) { background-color:#0000ff; } border-left: 11px solid #ccc; margin: 1.7em 0 1.7em 0.3em; background-color:#BFB; font-size:12px; line-height:65%; " // PTLQueue : Put(v) : // producer : partial method - waits as necessary assert v != null assert Mask = 1 && (Mask & (Mask+1)) == 0 // Document invariants // doorway step // Obtain a sequence number -- ticket // As a practical concern the ticket value is temporally unique // The ticket also identifies and selects a slot auto tkt = AtomicFetchIncrement (&PutCursor, 1) slot * s = &Slots[tkt & Mask] // waiting phase : // wait for slot's generation to match the tkt value assigned to this put() invocation. // The "generation" is implicitly encoded as the upper bits in the cursor // above those used to specify the index : tkt div (Mask+1) // The generation serves as an epoch number to identify a cohort of threads // accessing disjoint slots while s-Turn != tkt : Pause assert s-MailBox == null s-MailBox = v // deposit and pass message Take() : // consumer : partial method - waits as necessary auto tkt = AtomicFetchIncrement (&TakeCursor,1) slot * s = &Slots[tkt & Mask] // 2-stage waiting : // First wait for turn for our generation // Acquire exclusive "take" access to slot's MailBox field // Then wait for the slot to become occupied while s-Turn != tkt : Pause // Concurrency in this section of code is now reduced to just 1 producer thread // vs 1 consumer thread. // For a given queue and slot, there will be most one Take() operation running // in this section. // Consumer waits for producer to arrive and make slot non-empty // Extract message; clear mailbox; advance Turn indicator // We have an obvious happens-before relation : // Put(m) happens-before corresponding Take() that returns that same "m" for T v = s-MailBox if v != null : s-MailBox = null ST-ST barrier s-Turn = tkt + Mask + 1 // unlock slot to admit next producer and consumer return v Pause tryTake() : // total method - returns ASAP with failure indication for auto tkt = TakeCursor slot * s = &Slots[tkt & Mask] if s-Turn != tkt : return null T v = s-MailBox // presumptive return value if v == null : return null // ratify tkt and v values and commit by advancing cursor if CAS (&TakeCursor, tkt, tkt+1) != tkt : continue s-MailBox = null ST-ST barrier s-Turn = tkt + Mask + 1 return v The basic idea derives from the Partitioned Ticket Lock "PTL" (US20120240126-A1) and the MultiLane Concurrent Bag (US8689237). The latter is essentially a circular ring-buffer where the elements themselves are queues or concurrent collections. You can think of the PTLQueue as a partitioned ticket lock "PTL" augmented to pass values from lock to unlock via the slots. Alternatively, you could conceptualize of PTLQueue as a degenerate MultiLane bag where each slot or "lane" consists of a simple single-word MailBox instead of a general queue. Each lane in PTLQueue also has a private Turn field which acts like the Turn (Grant) variables found in PTL. Turn enforces strict FIFO ordering and restricts concurrency on the slot mailbox field to at most one simultaneous put() and take() operation. PTL uses a single "ticket" variable and per-slot Turn (grant) fields while MultiLane has distinct PutCursor and TakeCursor cursors and abstract per-slot sub-queues. Both PTL and MultiLane advance their cursor and ticket variables with atomic fetch-and-increment. PTLQueue borrows from both PTL and MultiLane and has distinct put and take cursors and per-slot Turn fields. Instead of a per-slot queues, PTLQueue uses a simple single-word MailBox field. PutCursor and TakeCursor act like a pair of ticket locks, conferring "put" and "take" access to a given slot. PutCursor, for instance, assigns an incoming put() request to a slot and serves as a PTL "Ticket" to acquire "put" permission to that slot's MailBox field. To better explain the operation of PTLQueue we deconstruct the operation of put() and take() as follows. Put() first increments PutCursor obtaining a new unique ticket. That ticket value also identifies a slot. Put() next waits for that slot's Turn field to match that ticket value. This is tantamount to using a PTL to acquire "put" permission on the slot's MailBox field. Finally, having obtained exclusive "put" permission on the slot, put() stores the message value into the slot's MailBox. Take() similarly advances TakeCursor, identifying a slot, and then acquires and secures "take" permission on a slot by waiting for Turn. Take() then waits for the slot's MailBox to become non-empty, extracts the message, and clears MailBox. Finally, take() advances the slot's Turn field, which releases both "put" and "take" access to the slot's MailBox. Note the asymmetry : put() acquires "put" access to the slot, but take() releases that lock. At any given time, for a given slot in a PTLQueue, at most one thread has "put" access and at most one thread has "take" access. This restricts concurrency from general MPMC to 1-vs-1. We have 2 ticket locks -- one for put() and one for take() -- each with its own "ticket" variable in the form of the corresponding cursor, but they share a single "Grant" egress variable in the form of the slot's Turn variable. Advancing the PutCursor, for instance, serves two purposes. First, we obtain a unique ticket which identifies a slot. Second, incrementing the cursor is the doorway protocol step to acquire the per-slot mutual exclusion "put" lock. The cursors and operations to increment those cursors serve double-duty : slot-selection and ticket assignment for locking the slot's MailBox field. At any given time a slot MailBox field can be in one of the following states: empty with no pending operations -- neutral state; empty with one or more waiting take() operations pending -- deficit; occupied with no pending operations; occupied with one or more waiting put() operations -- surplus; empty with a pending put() or pending put() and take() operations -- transitional; or occupied with a pending take() or pending put() and take() operations -- transitional. The partial put() and take() operators can be implemented with an atomic fetch-and-increment operation, which may confer a performance advantage over a CAS-based loop. In addition we have independent PutCursor and TakeCursor cursors. Critically, a put() operation modifies PutCursor but does not access the TakeCursor and a take() operation modifies the TakeCursor cursor but does not access the PutCursor. This acts to reduce coherence traffic relative to some other queue designs. It's worth noting that slow threads or obstruction in one slot (or "lane") does not impede or obstruct operations in other slots -- this gives us some degree of obstruction isolation. PTLQueue is not lock-free, however. The implementation above is expressed with polite busy-waiting (Pause) but it's trivial to implement per-slot parking and unparking to deschedule waiting threads. It's also easy to convert the queue to a more general deque by replacing the PutCursor and TakeCursor cursors with Left/Front and Right/Back cursors that can move either direction. Specifically, to push and pop from the "left" side of the deque we would decrement and increment the Left cursor, respectively, and to push and pop from the "right" side of the deque we would increment and decrement the Right cursor, respectively. We used a variation of PTLQueue for message passing in our recent OPODIS 2013 paper. ul { list-style:none; padding-left:0; padding:0; margin:0; margin-left:0; } ul#myTagID { padding: 0px; margin: 0px; list-style:none; margin-left:0;} -- -- There's quite a bit of related literature in this area. I'll call out a few relevant references: Wilson's NYU Courant Institute UltraComputer dissertation from 1988 is classic and the canonical starting point : Operating System Data Structures for Shared-Memory MIMD Machines with Fetch-and-Add. Regarding provenance and priority, I think PTLQueue or queues effectively equivalent to PTLQueue have been independently rediscovered a number of times. See CB-Queue and BNPBV, below, for instance. But Wilson's dissertation anticipates the basic idea and seems to predate all the others. Gottlieb et al : Basic Techniques for the Efficient Coordination of Very Large Numbers of Cooperating Sequential Processors Orozco et al : CB-Queue in Toward high-throughput algorithms on many-core architectures which appeared in TACO 2012. Meneghin et al : BNPVB family in Performance evaluation of inter-thread communication mechanisms on multicore/multithreaded architecture Dmitry Vyukov : bounded MPMC queue (highly recommended) Alex Otenko : US8607249 (highly related). John Mellor-Crummey : Concurrent queues: Practical fetch-and-phi algorithms. Technical Report 229, Department of Computer Science, University of Rochester Thomasson : FIFO Distributed Bakery Algorithm (very similar to PTLQueue). Scott and Scherer : Dual Data Structures I'll propose an optimization left as an exercise for the reader. Say we wanted to reduce memory usage by eliminating inter-slot padding. Such padding is usually "dark" memory and otherwise unused and wasted. But eliminating the padding leaves us at risk of increased false sharing. Furthermore lets say it was usually the case that the PutCursor and TakeCursor were numerically close to each other. (That's true in some use cases). We might still reduce false sharing by incrementing the cursors by some value other than 1 that is not trivially small and is coprime with the number of slots. Alternatively, we might increment the cursor by one and mask as usual, resulting in a logical index. We then use that logical index value to index into a permutation table, yielding an effective index for use in the slot array. The permutation table would be constructed so that nearby logical indices would map to more distant effective indices. (Open question: what should that permutation look like? Possibly some perversion of a Gray code or De Bruijn sequence might be suitable). As an aside, say we need to busy-wait for some condition as follows : "while C == 0 : Pause". Lets say that C is usually non-zero, so we typically don't wait. But when C happens to be 0 we'll have to spin for some period, possibly brief. We can arrange for the code to be more machine-friendly with respect to the branch predictors by transforming the loop into : "if C == 0 : for { Pause; if C != 0 : break; }". Critically, we want to restructure the loop so there's one branch that controls entry and another that controls loop exit. A concern is that your compiler or JIT might be clever enough to transform this back to "while C == 0 : Pause". You can sometimes avoid this by inserting a call to a some type of very cheap "opaque" method that the compiler can't elide or reorder. On Solaris, for instance, you could use :"if C == 0 : { gethrtime(); for { Pause; if C != 0 : break; }}". It's worth noting the obvious duality between locks and queues. If you have strict FIFO lock implementation with local spinning and succession by direct handoff such as MCS or CLH,then you can usually transform that lock into a queue. Hidden commentary and annotations - invisible : * And of course there's a well-known duality between queues and locks, but I'll leave that topic for another blog post. * Compare and contrast : PTLQ vs PTL and MultiLane * Equivalent : Turn; seq; sequence; pos; position; ticket * Put = Lock; Deposit Take = identify and reserve slot; wait; extract & clear; unlock * conceptualize : Distinct PutLock and TakeLock implemented as ticket lock or PTL Distinct arrival cursors but share per-slot "Turn" variable provides exclusive role-based access to slot's mailbox field put() acquires exclusive access to a slot for purposes of "deposit" assigns slot round-robin and then acquires deposit access rights/perms to that slot take() acquires exclusive access to slot for purposes of "withdrawal" assigns slot round-robin and then acquires withdrawal access rights/perms to that slot At any given time, only one thread can have withdrawal access to a slot at any given time, only one thread can have deposit access to a slot Permissible for T1 to have deposit access and T2 to simultaneously have withdrawal access * round-robin for the purposes of; role-based; access mode; access role mailslot; mailbox; allocate/assign/identify slot rights; permission; license; access permission; * PTL/Ticket hybrid Asymmetric usage ; owner oblivious lock-unlock pairing K-exclusion add Grant cursor pass message m from lock to unlock via Slots[] array Cursor performs 2 functions : + PTL ticket + Assigns request to slot in round-robin fashion Deconstruct protocol : explication put() : allocate slot in round-robin fashion acquire PTL for "put" access store message into slot associated with PTL index take() : Acquire PTL for "take" access // doorway step seq = fetchAdd (&Grant, 1) s = &Slots[seq & Mask] // waiting phase while s-Turn != seq : pause Extract : wait for s-mailbox to be full v = s-mailbox s-mailbox = null Release PTL for both "put" and "take" access s-Turn = seq + Mask + 1 * Slot round-robin assignment and lock "doorway" protocol leverage the same cursor and FetchAdd operation on that cursor FetchAdd (&Cursor,1) + round-robin slot assignment and dispersal + PTL/ticket lock "doorway" step waiting phase is via "Turn" field in slot * PTLQueue uses 2 cursors -- put and take. Acquire "put" access to slot via PTL-like lock Acquire "take" access to slot via PTL-like lock 2 locks : put and take -- at most one thread can access slot's mailbox Both locks use same "turn" field Like multilane : 2 cursors : put and take slot is simple 1-capacity mailbox instead of queue Borrow per-slot turn/grant from PTL Provides strict FIFO Lock slot : put-vs-put take-vs-take at most one put accesses slot at any one time at most one put accesses take at any one time reduction to 1-vs-1 instead of N-vs-M concurrency Per slot locks for put/take Release put/take by advancing turn * is instrumental in ... * P-V Semaphore vs lock vs K-exclusion * See also : FastQueues-excerpt.java dice-etc/queue-mpmc-bounded-blocking-circular-xadd/ * PTLQueue is the same as PTLQB - identical * Expedient return; ASAP; prompt; immediately * Lamport's Bakery algorithm : doorway step then waiting phase Threads arriving at doorway obtain a unique ticket number Threads enter in ticket order * In the terminology of Reed and Kanodia a ticket lock corresponds to the busy-wait implementation of a semaphore using an eventcount and a sequencer It can also be thought of as an optimization of Lamport's bakery lock was designed for fault-tolerance rather than performance Instead of spinning on the release counter, processors using a bakery lock repeatedly examine the tickets of their peers --

    Read the article

facebook twitter digg google delicious technorati stumbleupon myspace wordpress linkedin gmail igoogle windows live tumblr viadeo yahoo buzz yahoo mail yahoo bookmarks favorites email print

1