Race condition Example

Duration: 4 min

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Inside: a video lesson and guided study material.

Module outline

  1. General Intelligence & Reasoning: Analogy, Non Verbal Reasoning (Spatial Aptitude) (Spatial Reasoning) (Visual Reasoning), Series (Number and Letter Series) (Numerical Relations and Reasoning), Coding Decoding, Blood Relations, Directions (Direction Test), Ranking, Order and Sequence, Logical Sequence Of Words, Syllogisms, Venn Diagram, Deductive and Inductive Reasoning (Logical Deduction and Induction) (Prepositional Reasoning), Selection Decision Table (Decision Making), Data Sufficiency, Puzzle Solving (Puzzles), Data Arrangement, Cubes & Dices, Calendar, Clock, Arithmetic, Number System, HCF LCM, Verbal Analogy (Word Based Analogy), Visual Recognition and Figure Completion, Paper Folding and Cutting, Transformation of Shapes, Clocks and Calendars, Direction Sense, Cubes and Dice, Patterns in Two-Dimensional Figures, Seating Arrangements, Analogy and Classification, Logical Deduction and Induction, Alphabet and Word Tests, Mathematical Operations, Series Completion, Simplification and Approximation, Coding and Decoding, Numerical Reasoning, Assembling and Grouping of Shapes, Three-Dimensional Patterns and Visualization, Vocabulary, Number System, Averages, Mixtures and Alligation, Simple and Compound Interest, Percentages, Algebra, Speed, Time and Distance, Seating and Arrangement Puzzles, Traverse Surveying, Order, Ranking and Sequence, Constraint Puzzles, Syllogisms and Venn Diagrams, Reading Comprehension, Critical Reasoning, Permutations and Combinations, Narrative Sequencing, Project Monitoring, Resources and Safety, Profit, Loss and Discount, Ratio and Proportion, Time and Work, Mensuration, Data Interpretation, Powers, Surds and Logarithms, Sequences and Series, Articles and Determiners, Sentence Completion, Data Sufficiency, Blood Relations, Simple Interest and Compound Interest, Mixture and Alligation, Sequence and Series (Series), Speed Time and Distance, Algebra, Profit and Loss, Powers and Exponents (Surds and Indices), Permutation and Combination
  2. General Awareness: Physics, Chemistry, Biology, History, Geography, Polity, Indian Economy, Environment, Static General Knowledge, GK- Current Affairs, Artificial Intelligence, MS Office Applications, Terms & Abbreviations, Keyboard Shortcuts, Evolution of Indian Banking (Banking & Financial Awareness), Emerging Tech Trends
  3. Engineering Mathematics: Set Theory, Relations, Functions, Graph Theory, Group Theory, Propositional and Predicate Logic, Linear Algebra, Calculus, Probability, Statistics, Signal Space and Optimum Detection, Probability, Statistics
  4. Digital Logic: Digital Systems & Boolean Basics, Logic Gates & Hardware, Boolean Expression, Boolean Minimization, Combinational Circuit, Sequential Circuits, Number System, Number Representation, Floating Point Rep, Number Systems and Codes, Registers and Counters, Boolean Algebra and Logic Gates, Microprocessors and Microcontrollers, Logic Families and CMOS Logic, Microprocessors, Logic Gates and Boolean Algebra, Minimization of Boolean Functions, Timing, Hazards and Testing, Logic Families, Combinational Logic Design, Arithmetic Circuits, Waveform Generators and Timer Circuits, Semiconductor Memories and Programmable Logic Devices, Combinational Logic Circuits, Latches and Flip-Flops, Finite State Machines, Sequential Circuits and State Machines, Minimization of Boolean Functions, Arithmetic Circuits, Latches and Flip-Flops, Number Systems and Codes, Registers and Counters
  5. Computer Organisation & Architecture: Basics of COA, Cache Memory Organization, Input Output Organisation, Pipelining, Instr Formats & Modes, Control Unit Design, Programming the Basic Computer, Register Transfer and Microoperations, Semiconductor Memories and Programmable Logic, Processor Organization and Instructions, Memory Hierarchy and Input/Output, Registers and Counters
  6. Programming & Data Structures: C Fundamentals, Control Flow, Functions, Arrays & Pointers, Storage Classes, Structures & Enums, DMA, Macros, Scoping & File Handling, Introduction to DS, Array, Stack, Queue, Linked List, Tree, Graphs, Hashing, HTML Basics, OOPS with C++, Java, Object Oriented Technology
  7. Databases: Basics of DBMS, ER Diagram, Relational Model & Functional Dependencies, Keys & Integrity Constraints, Normalization (1NF - BCNF), Decomposition Properties & 4NF, File Organization & Indexing, Relational Algebra, SQL, Relational Calculus, Transaction Management, Concurrency Control, Database Recovery, Database Security & Authorization
  8. Algorithms: Algorithm Analysis, Time Complexity Analysis, Sorting Algorithms, Greedy Algorithms, Dynamic Programming, Minimum Spanning Trees, Shortest Path Algos
  9. Theory of Computation: Introduction to TOC, Deterministic FA (DFA), Non-Deterministic FA, Regular Expressions, Grammar, Regular Language Properties, Moore & Mealy Machines, Pushdown Automata & CFG, Turing Machines, Complexity Theory
  10. Compiler Design: Intro to Compilers, Lexical Analysis, Grammar & CFG, Syntax Analysis: Top-Down, Syntax Analysis: Bottom-Up, Semantic Analysis & SDT, Intermediate Code Gen, Code Optimization, Run Time Environment
  11. Operating System: Introduction to OS, Process Management, CPU Scheduling, Process Synchronization, Threads & Process Creation, Deadlock, Memory Management, Virtual Memory, Disc Scheduling, File Management, Security, Windows OS, Distributed Systems, Unix OS, Linux OS
  12. Computer Networks: Introduction to CN, DLL: Access Control, DLL: Flow Control, DLL: Error Control, DLL: Framing, Data Link Layer - Ethernet, Net Layer: IPv4 & Proto, Net Layer: IP Addressing, Net Layer:Routing Protocol, Transport Layer Services, TL: Congestion & UDP, Application Layer, Hardware Basics, Data Communication, Website, Browser & Services, Web Design & Development, Network Security, Cyber Threats and Malware Attacks, Cyber Safety and Security
  13. Full Length Mock Tests:
  14. Sectional Tests:
  15. Paper 2 - Full-length Mock Tests:
AI summary & chapters

AI Summary

An AI-generated summary of this video lecture.

This video solves a GATE-2015 operating-systems concurrency question. Two functions, P1 and P2, share a variable B with initial value 2. P1 executes C = B - 1; then B = 2 * C;, while P2 executes D = 2 * B; then B = D - 1;. The question asks for the number of distinct values that B can possibly take after execution. The instructor labels the four instructions I11, I12 for P1 and I21, I22 for P2. Because each function's two instructions must preserve their internal order, the possible interleavings are the six permutations of choosing which P1 instruction and which P2 instruction occur at each step. A table with Case 1 through Case 6 lists the six interleavings of I11, I12, I21, and I22. The instructor evaluates each case by tracking the shared variable B (and local variables C and D) through the sequence. For example, one interleaving gives I11: C = 2 - 1 = 1; then I21: D = 2 * 2 = 4; then I12: B = 2 * 1 = 2; then I22: B = 4 - 1 = 3. Other interleavings yield final values such as 2 and 3 (and in some orderings, other intermediate results). By circling the final B values across all six cases and removing duplicates, the instructor concludes that B can take 3 distinct final values. The answer '3' is circled at the bottom of the question slide.

Chapters

  1. 0:00 – 2:00 00:00-02:00

    The slide presents the GATE-2015 question in an orange-and-white two-column table labeled P1() and P2(). The top line states that the two functions share a variable B with an initial value of 2 and execute concurrently. P1 contains 'C = B - 1;' then 'B = 2 * C;'; P2 contains 'D = 2 * B;' then 'B = D - 1;'. The red bottom line asks for the number of distinct values B can possibly take after execution. Handwritten blue annotations progressively label the P1 steps as I1, J1 and the P2 steps as I2, J2 (later refined to I11, I12 and I21, I22), establishing the instruction labels used for interleaving analysis.

  2. 2:00 – 3:58 02:00-03:58

    The slide now shows two code blocks headed P1() and P2() with labeled instructions (I11) C = B - 1;, (I12) B = 2 * C; and (I21) D = 2 * B;, (I22) B = D - 1;. Below, a green-headed table lists six columns Case1 through Case6, each containing a vertical sequence of the four instruction labels in different orders. Blue vertical line marks highlight selected rows in Case1-Case4 as the instructor computes each interleaving. On-screen values such as C=1, D=4, B=2 appear during the step-by-step evaluation. The instructor circles key intermediate values (e.g., B=3) and crosses out redundant steps, then returns to the original question slide where the final answer '3' is circled at the bottom, indicating three distinct possible values for B.

The core teaching point is systematic enumeration of legal interleavings in a concurrent execution where each process's internal instruction order must be preserved. With two instructions per process, there are C(4,2) = 6 valid interleavings, which the instructor tabulates as Case1-Case6. The method is: (1) label each instruction, (2) list all order-preserving interleavings, (3) simulate the shared variable B through each sequence while tracking local variables C and D, (4) collect the final B values and count distinct ones. The worked example shows how one interleaving produces C=1, D=4, and a final B=3, while others produce different finals. The conclusion is that the number of distinct values B can take is 3, which is circled as the answer. This case-by-case table method is the key exam technique for GATE concurrency questions of this type.

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