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Leveling Up My GraphQL Skills: Real Time Subscriptions

GraphQL Yatiñanakaj Nivelar: Chiqpach Tiempo Suscripciones

Poboljšavam svoje GraphQL vještine: Pretplate u realnom vremenu

Mejorando mis habilidades en GraphQL: suscripciones en tiempo real

Améliorer mes compétences GraphQL : abonnements en temps réel

Aumentando de nivel as miñas habilidades de GraphQL: subscricións en tempo real

Իմ GraphQL հմտությունների մակարդակի բարձրացում. իրական ժամանակի բաժանորդագրություններ

GraphQL スキルをレベルアップ: リアルタイム サブスクリプション

Manatsara ny fahaizako amin'ny GraphQL: Famandrihana amin'ny fotoana tena izy

Миний GraphQL ур чадварыг дээшлүүлэх: Бодит цагийн захиалга

Go Lekantšha Mabokgoni a Ka a GraphQL: Dipeeletšo tša Nako ya Sebele

Nâng cao kỹ năng GraphQL của tôi: Đăng ký theo thời gian thực

提升我的 GraphQL 技能：实时订阅

This paper is available on arxiv under CC BY-NC-SA 4.0 DEED license. Authors: (1) Pascal Baumann, Max Planck Institute for Software Systems (MPI-SWS), Germany; (2) Rupak Majumdar, Max Planck Institute for Software Systems (MPI-SWS), Germany; (3) Ramanathan S. Thinniyam, Max Planck Institute for Software Systems (MPI-SWS), Germany; (4) Georg Zetzsche, Max Planck Institute for Software Systems (MPI-SWS), Germany. Table of Links Introduction Dynamic Networks of Concurret Pushdown Systems (DCPS) Warm-up: Non-Termination Fair Non-Termination From Progressive Runs for VASSB to Reachability Starvation Conclusion, Acknowledgment & References A. Strengthening Fairness to Progressive Runs B. Proofs from Section 4.1 C. Proofs for Section 5 D. Proofs for Section 5.3 E. Proofs for Section 6 We study context-bounded verification of liveness properties of multi-threaded, shared-memory programs, where each thread can spawn additional threads. Our main result shows that context-bounded fair termination is decidable for the model; context-bounded implies that each spawned thread can be context switched a fixed constant number of times. Our proof is technical, since fair termination requires reasoning about the composition of unboundedly many threads each with unboundedly large stacks. In fact, techniques for related problems, which depend crucially on replacing the pushdown threads with finite-state threads, are not applicable. Instead, we introduce an extension of vector addition systems with states (VASS), called VASS with balloons (VASSB), as an intermediate model; it is an infinite-state model of independent interest. A VASSB allows tokens that are themselves markings (balloons). We show that context bounded fair termination reduces to fair termination for VASSB. We show the latter problem is decidable by showing a series of reductions: from fair termination to configuration reachability for VASSB and thence to the reachability problem for VASS. For a lower bound, fair termination is known to be non-elementary already in the special case where threads run to completion (no context switches). We also show that the simpler problem of context-bounded termination is 2EXPSPACE-complete, matching the complexity bound—and indeed the techniques—for safety verification. Additionally, we show the related problem of fair starvation, which checks if some thread can be starved along a fair run, is also decidable in the context-bounded case. The decidability employs an intricate reduction from fair starvation to fair termination. Like fair termination, this problem is also non-elementary. 1 INTRODUCTION We study decision problems related to liveness verification of shared-memory multithreaded programs. In a shared-memory multithreaded program, a number of threads execute concurrently. Each thread executes possibly recursive sequential code, and can spawn new threads for concurrent execution. The threads communicate through shared global variables that they can read and write. The execution of the program is guided by a non-deterministic scheduler that picks one of the spawned threads to execute in each time step. If the scheduler replaces the currently executing thread with a different one, we say the current active thread is context switched. Shared-memory multithreaded programming is ubiquitous and static verification of safety or liveness properties of such programs is a cornerstone of formal verification research. Indeed, there is a vast research literature on the problem—from a foundational understanding of the computability and complexity of (subclasses of) models, to program logics, and to efficient tools for analysis of real systems. In this paper, we focus on decidability issues for liveness verification for multithreaded shared memory programs with the ability to spawn threads. Liveness properties, intuitively, specify that “something good” happens when a program executes. A simple example of a liveness property is termination: the property that a program eventually terminates. In fact, termination is a “canonical” liveness property: for a very general class of liveness properties, through monitor constructions, verifying liveness properties reduces to verifying termination [Apt and Olderog 1991; Vardi 1991]. Unfortunately, under the usual notion of non-deterministic schedulers, some programs may fail to terminate for uninteresting reasons. Consider the following program: 1 global bit := 1; 2 main () { spawn foo ; spawn bar ; } 3 foo () { if bit = 1 then spawn foo ; } 4 bar () { bit := 0; } A main thread spawns two additional threads foo and bar. The thread foo checks if a global bit is set and, if so, re-spawns itself. The thread bar resets the global bit. There is a non-terminating execution of this program in which bar is never scheduled. However, a scheduler that never schedules a thread that is ready to run would be considered unfair. Instead, one formulates the problem of fair termination: termination under a fair non-deterministic scheduler. We abstract away from the exact mechanism of the scheduler, and only require that every spawned thread that is infinitely often ready to run is eventually scheduled. Then, every fair run of the above program is terminating: eventually bar is scheduled, after which foo does not spawn a new thread. Since the high undecidability relies on an unbounded exchange of information among threads, a recent and apposite approach to verifying concurrent recursive programs is to explore only a representative subset of program behaviors by limiting the number of inter-thread interactions [Musuvathi and Qadeer 2007; Qadeer and Rehof 2005]. This approach, called context bounding by Qadeer and Rehof [2005], considers the verification problem as a family of problems, one for each K. The K-context bounded instance, for any fixed K ≥ 0, considers only those executions where each thread is context switched at most K times by the scheduler. In the limit as K → ∞, the K-bounded approach explores all behaviors where each thread runs a finite number of times. In practice, bounded explorations with small values of K have proved to be effective to uncover many safety and liveness bugs in real systems. Our results generalize the special case of K = 0 studied by Ganty and Majumdar [2012] as asynchronous programs. When K = 0, each thread executes to completion without being interrupted in the middle. Ganty and Majumdar show the decidability of safety and liveness verification for this model. In particular, they prove safety and termination are both EXPSPACE-complete and fair termination and fair starvation are decidable but non-elementary.[2] Their proof depends on the observation that, since threads are not interrupted, one can replace the pushdown automata for each thread by finite automata that accept Parikh-equivalent languages. Unfortunately, their technique does not generalize when context switches are allowed. For K ≥ 1, Atig et al. [2009] showed that the safety verification problem is decidable in 2EXPSPACE. Ten years later, a matching lower bound was shown by Baumann et al. [2020]. The key observation in the decision procedure is that safety is preserved under downward closures: one can analyze a related program where some spawned threads are “forgotten.” Since the downward closure of a context free language is effectively regular, one can replace the pushdown automaton for each thread by a finite automaton accepting the downward closure. In fact, our proof of termination also follows easily from this observation, as termination is also preserved by downward closures. Unfortunately, fair termination and fair non-starvation are not preserved under downward closures. Thus, we cannot apply the preceding techniques to replace pushdown automata by finite automata in our construction. Thus, our proof is more intricate and requires several insights into the computational model. The key difficulty in our decision procedure is to maintain a finite representation for unboundedly many active threads, each with unboundedly large local stacks and potentially spawning unboundedly many new threads, and to compose their context-switched executions into a global execution. In order to maintain and compose such configurations, we introduce a new model, called VASS with balloons (VASSB), that extends the usual model of a vector addition systems with states (VASS) with “balloons”: a token in a VASSB can be a usual VASS token or a balloon token that is itself a vector. Intuitively, balloon tokens represent the possible new threads a thread can spawn along one of its execution segments. We show through a series of constructions that the fair termination problem reduces to the fair termination problem for VASSB, and thence to the configuration reachability problem for VASSB. Finally, we show that configuration reachability for VASSB is decidable by a reduction to the reachability problem for VASS. This puts VASSB in the rare class of infinite-state systems which generalize VASS and yet maintain a decidable reachability (not just coverability!) problem. Finally, we show a reduction from the fair starvation problem to fair termination. The reduction relies on two combinatorial insights. The first is that if a program has an infinite fair run, then it has one in which there exists a bound on the number of threads spawned by each thread. The second is a novel pumping argument based on Ramsey’s theorem; it implies that it suffices to track a finite amount of data about each thread to determine whether some thread can be starved. In conclusion, we prove decidability of liveness verification for multithreaded shared memory programs with the ability to dynamically spawn threads, an extremely expressive model of multithreaded programming. This model sits at the boundary of decidability and subsumes many other models studied before. Safety verification for concurrent recursive programs is already undecidable with just two threads and finite global store [Ramalingam 2000]. Many results on context-bounded safety verification consider a model with a fixed number of threads, without spawns. The complexity of safety verification for this model is well understood at this point. The key idea underlying the best algorithms reduce the problem to analyzing a sequential pushdown system [Lal and Reps 2009] by guessing the bounded sequences of context switches for each thread and using the finite state to ensure the sequential runs can be stitched together Related Work. When the model allows spawning of new threads, as ours does, existing decision procedures are significantly more complex, both in their technicalities and in computational cost. There are relatively few results on decidability of liveness properties of infinite-state systems. Atig et al. [2012a] show a sufficient condition for fair termination for context-bounded executions of a fixed number of threads, where they look for ultimately periodic executions, in which each thread is context switched at most K times in the loop. They show that the search for such ultimately periodic executions can be reduced to safety verification. In our model, fair infinite runs may involve unboundedly many threads with unbounded stacks and need not be periodic—for example, there can always be more and more newly spawned threads. Multi-pushdown systems model multithreaded programs with a fixed number of threads. Many decision procedures are known when the executions of such systems are restricted through different bounds such as context, scope, or phase [Atig et al. 2012b, 2017; Torre et al. 2016], and also through limitations on communication patterns [Lal et al. 2008]. These problems are orthogonal to us, either in the modeling capabilities or in the properties verified. Decidability of linear temporal logic is known for weaker models of multithreaded recursive programs, such as symmetric parameterized programs [Kahlon 2008] or leader-follower programs with non-atomic reads and writes [Durand-Gasselin et al. 2017; Fortin et al. 2017; Muscholl et al. 2017]. These programs cannot perform compare-and-swap operations, and therefore, their computational power is quite limited (in fact, LTL model checking is PSPACE-complete). A number of heuristic approaches to fair termination of multithreaded programs provide sound but incomplete algorithms, but for a more general class of programs involving infinite-state data variables [Cook et al. 2007, 2011; Farzan et al. 2016; Kragl et al. 2020; Padon et al. 2018]. The goal there is to provide a sound proof rule for verification but not to prove a decidability result. In terms of fair termination problems for VASS, the theme of computational hardness continues. For example, the classical notion of fair runs, in which an infinitely activated transition has to be fired infinitely often, leads to undecidability [Carstensen 1987] and even Σ 1 1 - completeness [Howell et al. 1991]. However, weakly fair termination, where only those transitions that are almost always activated have to be fired infinitely often, is decidable [Jančar 1990]. A rich taxonomy of fairness notions with corresponding decidability results can be found in [Howell et al. 1991]. However, all of these notions appear to be incomparable with our fairness notion for VASSB. Our model of VASSB treads the boundary of models that generalize VASS for which reachability can be proved to be decidable. We note that there are several closely related models, VASS with a stack [Leroux et al. 2015] and branching VASS [Verma and Goubault-Larrecq 2005], for which decidability of reachability is a long-standing open problem, and others, nested Petri nets [Lomazova and Schnoebelen 1999], for which reachability is undecidable. [1] Recall that the class Π 1 1 in the analytic hierarchy is the class of all relations on N that can be defined by a universal second-order number-theoretic formula. [2] Their result shows a polynomial-time equivalence between fair termination and reachability in vector addition systems with states (VASS, a.k.a. Petri nets). The complexity bounds follow from our current knowledge of the complexity of VASS reachability [Czerwinski et al. 2019].

Context-Bounded Verification of Liveness Properties for
Multithreaded Shared-Memory Programs: Intro

On Combinations of Masters against the public

In the world of high fashion, few names resonate as strongly as Versace. While the brand itself has become synonymous with opulence and luxury, one name within its legacy stands out prominently – Donatella Versace. Beyond the shimmering fabrics and iconic designs, Donatella's life story unfolds as a testament to resilience, creativity, and the intersection of personal struggles with professional success. Donatella Versace: A Fashion Icon's Journey: Donatella Versace, born on May 2, 1955, in Reggio Calabria, Italy, was thrust into the limelight when her brother Gianni Versace founded the eponymous fashion house in 1978. Initially, she played a supporting role, contributing to the design process and managing the public relations aspect of the brand. However, tragedy struck in 1997 when Gianni was tragically murdered, leaving Donatella to step into the role of the creative force behind the fashion empire. Donatella's design aesthetic has been defined by boldness, sensuality, and a keen eye for innovation. Her creations often blur the lines between fashion and art, reflecting her fearless approach to design. From iconic red carpet gowns to cutting-edge ready-to-wear collections, Donatella's imprint on the fashion industry is indelible. Mental Health Struggles and Resilience: Behind the glamorous facade, Donatella Versace has openly discussed her struggles with mental health. The intense pressure of leading one of the world's most influential fashion houses, coupled with the grief from her brother's death, took a toll on her well-being. In interviews, Donatella has shared her journey of overcoming addiction, finding strength in vulnerability, and using her experiences to advocate for mental health awareness. Donatella's openness about her mental health challenges has shattered the stereotype that success in the fashion industry comes without personal costs. By sharing her story, she has become a beacon of hope for those grappling with similar issues, proving that vulnerability and strength are not mutually exclusive. Fashion as a Therapeutic Outlet: For Donatella Versace, fashion isn't just a career; it's a therapeutic outlet and a form of self-expression. Through her designs, she has channeled her emotions, creating pieces that resonate with power, resilience, and the beauty of overcoming adversity. The bold colors, intricate patterns, and daring silhouettes in her collections are not just fashion statements; they are declarations of strength and triumph over personal struggles. Mental Health Advocacy: Donatella Versace's journey through mental health challenges has also led her to become a vocal advocate for mental health awareness. She has used her platform to destigmatize mental health issues, encouraging open conversations and promoting understanding. In 2018, she collaborated with Lady Gaga on the "Versace on the Floor" campaign, . which aimed to raise funds for Gaga's Born This Way Foundation, which focused on mental health support Donatella Versace's life is a captivating narrative of resilience, creativity, and the intricate dance between personal struggles and professional triumphs. Through her contributions to the fashion world and her candid discussions about mental health, she has become a symbol of strength and authenticity. Donatella Versace's legacy is not only stitched into the fabric of high fashion but also etched into the ongoing conversation about mental health, reminding us that even in the glitzy world of couture, humanity remains at the core. Also published . here

Resilience in Couture: Donatella Versace's Journey Through Fashion and Mental Health

OF THE PLAN FOR REFORMING THE SOCIETY.

A Treatise on Domestic Economy; For the Use of Young Ladies at Home and at School by Catharine Esther Beecher, is part of the HackerNoon Books Series. You can jump to any chapter in this book . ON THE CARE OF CHAMBERS AND BEDROOMS. here CHAPTER XXXI. ON THE CARE OF CHAMBERS AND BEDROOMS. Every mistress of a family should see, not only that all sleeping-rooms in her house well ventilated at night, but that they actually are so. Where there is no open fireplace to admit the pure air from the exterior, a door should be left open into an entry, or room where fresh air is admitted; or else a small opening should be made in a window, taking care not to allow a draught of air to cross the bed. The debility of childhood, the lassitude of domestics, and the ill-health of families, are often caused by neglecting to provide a supply of pure air. Straw matting is best for a chamber carpet, and strips of woollen carpeting may be laid by the side of the bed. Where chambers have no closets, a is indispensable. This is a moveable closet, with doors, divided, by a perpendicular partition, into two apartments. In one division, rows of hooks are placed, on which to hang dresses. The other division is fitted up with shelves, for other uses. Some are made with drawers at the bottom for shoes, and such like articles. A low square box, set on casters, with a cushion on the top, and a drawer on one side to put shoes in, is a great convenience in dressing the feet. An old champaigne basket, fitted up with a cushion on the lid, and a valance fastened to it to cover the sides, can be used for the same purpose. can be wardrobe A comfortable couch, for chambers and sitting-rooms, can be made by a common carpenter, at a small expense. Have a frame made (like the annexed engraving, Fig. ,) of common stuff, six feet long, twenty-eight inches wide, and twelve inches high. It must be made thus low, because the casters and cushions will raise it several inches. Have the sloping side-piece, , and head-piece, , sawed out of a board; nail brown linen on them, and stuff them with soft hay or hair. Let these be screwed to the frame, and covered with furniture patch. Then let slats be nailed across the bottom, as at , , four inches apart. This will cost two or three dollars. Then make a thick cushion, of hay or straw, with side strips, like a mattress, and lay this for the under-cushion. To put over this, make a thinner cushion, of hair, cover it with furniture-calico, and fasten to it a valance reaching to the floor. Then make two square pillows, and cover them with calico, like the rest. Both the cushions should be stitched through like mattresses. 38 a b c c The writer has seen a couch of this kind, in a common parlor, which cost less than eight dollars, was much admired, and was a constant comfort to the feeble mother, as well as many other members of the family. Another convenience, for a room where sewing is done in Summer, is a fancy-jar, set in one corner, to receive clippings, and any other rubbish. It can be covered with prints, or paintings, and varnished; and then looks very prettily. The trunks in a chamber can be improved in looks and comfort, by making cushions of the same size and shape, stuffed with hay and covered with chintz, with a frill reaching nearly to the floor. Every bedchamber should have a washstand, bowl, pitcher, and tumbler, with a washbucket under the stand, to receive slops. A light screen, made like a clothes-frame, and covered with paper or chintz, should be furnished for bedrooms occupied by two persons, so that ablutions can be performed in privacy. It can be ornamented, so as to look well anywhere. A little frame, or towel-horse, by the washstand, on which to dry towels, is a convenience. A washstand should be furnished with a sponge or washcloth, and a small towel, for wiping the basin after using it. This should be hung on the washstand or towel-horse, for constant use. A soap-dish, and a dish for toothbrushes, are neat and convenient, and each person should be furnished with two towels; one for the feet, and one for other purposes. It is in good taste to have the curtains, bedquilt, valance, and window-curtains, of similar materials. In making featherbeds, side-pieces should be put in, like those of mattresses, and the bed should be well filled, so that a person will not be buried in a hollow, which is not healthful, save in extremely cold weather. Featherbeds should never be used, except in cold weather. At other times, a thin mattress of hair, cotton and moss, or straw, should be put over them. A simple strip of broad straw matting, spread over a featherbed, answers the same purpose. Nothing is more debilitating, than, in warm weather, to sleep with a featherbed pressing round the greater part of the body. Pillows stuffed with papers an inch square, are good for Summer, especially for young children, whose heads should be kept cool. The cheapest and best covering of a bed, for Winter, is a , made to contain three or four pounds of cotton, laid in batts or sheets, between covers tacked together at regular intervals. They should be three yards square, and less cotton should be put at the sides that are tucked in. It is better to have two thin comforters, to each bed, than one thick one; as then the covering can be regulated according to the weather. cotton comforter Few domestics will make a bed properly, without much attention from the mistress of the family. The following directions should be given to those who do this work. Open the windows, and lay off the bed-covering, on two chairs, at the foot of the bed. After the bed is well aired, shake the feathers, from each corner to the middle; then take up the middle, and shake it well, and turn the bed over. Then push the feathers in place, making the head higher than the foot, and the sides even, and as high as the middle part. Then put on the bolster and the under sheet, so that the wrong side of the sheet shall go next the bed, and the come at the head, tucking in all around. Then put on the pillows, even, so that the open ends shall come to the sides of the bed, and then spread on the upper sheet, so that the wrong side shall be next the blankets, and the marked end at the head. This arrangement of sheets is to prevent the part where the feet lie from being reversed, so as to come to the face, and also to prevent the parts soiled by the body from coming to the bedtick and blankets. Then put on the other covering, except the outer one, tucking in all around, and then turn over the upper sheet, at the head, so as to show a part of the pillows. When the pillow-cases are clean and smooth, they look best outside of the cover, but not otherwise. Then draw the hand along the side of the pillows, to make an even indentation, and then smooth and shape the whole outside. A nice housekeeper always notices the manner in which a bed is made; and in some parts of the Country, it is rare to see this work properly performed. marking The writer would here urge every mistress of a family, who keeps more than one domestic, to provide them with single beds, that they may not be obliged to sleep with all the changing domestics, who come and go so often. Where the room is too small for two beds, a narrow trucklebed under another, will answer. Domestics should be furnished with washing conveniences in their chambers, and be encouraged to keep their persons and rooms neat and in order. On Packing and Storing Articles. Fold a gentleman's coat, thus:—Lay it on a table or bed, the inside downward, and unroll the collar. Double each sleeve once, making the crease at the elbow, and laying them so as to make the fewest wrinkles, and parallel with the skirts. Turn the fronts over the back and sleeves, and then turn up the skirts, making all as smooth as possible. Fold a shirt, thus:—One that has a bosom-piece inserted, lay on a bed, bosom downward. Fold each sleeve twice, and lay it parallel with the sides of the shirt. Turn the two sides, with the sleeves, over the middle part, and then turn up the bottom, with two folds. This makes the collar and bosom lie, unpressed, on the outside. Fold a frock thus:—Lay its front downward, so as to make the first creases in folding come in the side breadths. To do this, find the middle of the side breadths by first putting the middle of the front and back breadths together. Next, fold over the side creases so as just to meet the slit behind. Then fold the skirt again, so as to make the backs lie together within and the fronts without. Then arrange the waist and sleeves, and fold the skirt around them. In packing trunks, for travelling, put all heavy articles at the bottom, covered with paper, which should not be printed, as the ink rubs off. Put coats and pantaloons into linen cases, made for the purpose, and furnished with strings. Fill all crevices with small articles; as, if a trunk is not full, nor tightly packed, its contents will be shaken about, and get injured. A thin box, the exact size of the trunk, with a lid, and covered with brown linen, is a great convenience, to set inside, on the top of the trunk, to contain light articles which would be injured by tight packing. Have straps, with buckles, fastened to the inside, near the bottom, long enough to come up and buckle over this box. By this means, when a trunk is not quite full, this box can be strapped over so tight, as to keep the articles from rubbing. Under-clothing packs closer, by being rolled tightly, instead of being folded. Bonnet-boxes, made of light wood, with a lock and key, are better than the paper bandboxes so annoying to travellers. Carpet bags are very useful, to carry the articles to be used on a journey. The best ones have sides inserted, iron rims, and a lock and key. A large silk travelling-bag, with a double linen lining, in which are stitched receptacles for toothbrush, combs, and other small articles, is a very convenient article for use when travelling. A bonnet-cover, made of some thin material, like a large hood with a cape, is useful to draw over the bonnet and neck, to keep off dust, sun, and sparks from a steam engine. Green veils are very apt to stain bonnets, when damp. In packing household furniture, for moving, have each box numbered, and then have a book, in which, as each box is packed, note down the number of the box, and the order in which its contents are packed, as this will save much labor and perplexity when unpacking. In packing china and glass, wrap each article, separately, in paper, and put soft hay or straw at bottom and all around each. Put the heaviest articles at the bottom; and on the top of the box, write, "This side up.” About HackerNoon Book Series: We bring you the most important technical, scientific, and insightful public domain books. This book is part of the public domain. Catharine Esther Beecher (2007). A Treatise on Domestic Economy; For the Use of Young Ladies at Home and at School. Urbana, Illinois: Project Gutenberg. Retrieved https://www.gutenberg.org/cache/epub/21829/pg21829-images.html This eBook is for the use of anyone anywhere at no cost and with almost no restrictions whatsoever. You may copy it, give it away or re-use it under the terms of the Project Gutenberg License included with this eBook or online at , located at . www.gutenberg.org https://www.gutenberg.org/policy/license.html

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