Chapter 5: Synchronization

Critical Section Conditions

• Mutual Exclusion: Only one process may be in the critical section at a time.
• Progress: If the critical section is empty, some waiting process can enter.
• Bounded Waiting: No starvation; each process waits a bounded number of turns.

Atomic Instructions

• Test-and-Set: old = *b; *b = TRUE; return old
• Swap: temp = *a; *a = *b; *b = temp

Spinlocks

• TAS:

  bool m = false;
  lock() { while (TestAndSet(&m)); }
  unlock() { m = false; }
  

• Swap:

  bool m = false;
  lock() { bool key = true; while (key) Swap(&m, &key); }
  unlock() { m = false; }
  

Semaphores

• wait(S): S.val--; if S.val < 0 block
• signal(S): S.val++; if S.val <= 0 wake one
• Binary semaphore as mutex: init = 1; lock = wait; unlock = signal

Peterson's

Chemistry Fundamentals and Reactions

Chemical Bonding Types

• Ionic Bonding: Metal + Non-metal → Electrons are transferred.
• Covalent Bonding: Non-metal + Non-metal → Electrons are shared.

Chemical Naming Conventions

• Ionic Naming: Metal + Non-metal (ending in “-ide”). Use Roman numerals for multivalent metals. Includes polyatomic ions.
• Molecular Compounds: Use prefixes (mono-, di-, tri-, etc.).
• Diatomic Elements: H₂, O₂, F₂, Br₂, I₂, N₂, Cl₂.

Properties of Compounds

• Ionic Compounds: Solid state, high melting/boiling points, conducts electricity when dissolved (aqueous).
• Molecular Compounds: Low melting/boiling points, poor electrical conductors.

Balancing Chemical Equations

The process follows the Law of Conservation of Mass:

1. Word Equation
2. Skeleton

Fundamental Accounting Equations

• Assets = Liabilities + Equity
• Net Income = Revenues - Expenses
• Gross Profit = Sales - Cost of Goods Sold (COGS)
• Operating Income = Gross Profit - Operating Expenses
• Income Before Tax = Operating Income ± Non-operating Items
• Net Income = Income Before Tax - Tax Expense
• Ending Retained Earnings = Beginning Retained Earnings + Net Income - Dividends

Cash Flow and Adjusting Entries

• Free Cash Flow = Operating Cash Flow - Capital Expenditures
• Change in Cash = Cash Flow from Operating + Investing + Financing
• Accrued Revenue → Revenue ↑, Receivable ↑
• Accrued Expense → Expense ↑, Payable ↑
• Deferred Revenue → Unearned Revenue ↓, Revenue ↑
• Prepaid Expense → Prepaid Asset ↓, Expense ↑
• Depreciation → Depreciation

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FOR AND AGAINST

For and Against: Introduction

It is widely known… Are you one of those people who thinks that…? There are many people who believe the following.

For

On the one hand, those who believe… A further advantage of... is …

Against

On the other hand, those who are against… One major disadvantage of… An additional drawback of ...

Conclusión

To sum up, there are strong arguments both for and against… Although… I believe

FORMAL EMAIL

Formal Email: Complaint Example

I am writing to you to formally complain about… I strongly believe… My name is…

Structure:

• Firstly, ….
• Moreover, …
• In addition, …

Polite closing: I would appreciate it if you could resolve this matter promptly. I look forward to your response. Please do not hesitate... Continue reading "For and Against Arguments, Email Samples & Opinion Essay Examples" »

The History of Al-Andalus (711–1492)

Al-Andalus was the Muslim state established in the Iberian Peninsula in the 8th century. Its borders and government changed significantly over the centuries, primarily due to internal disputes between different groups.

The Conquest of the Iberian Peninsula (711–718)

In 711, a small Muslim group led by Tariq crossed the Strait of Gibraltar and defeated the Visigoths at the Battle of Guadalete. The Visigothic Kingdom was suffering an economic crisis, which facilitated the advance of subsequent Muslim armies. By 722, they controlled almost all the peninsula except a narrow strip in the north where the Hispano-Visigoths took refuge.

After conquering Hispania, the Umayyad Caliph of Damascus established the Emirate... Continue reading "Al-Andalus: Islamic Rule and Medieval Iberian Kingdoms" »

Time Series Analysis

Identifying Trends

• Upward trend: Data increases over time.
• Downward trend: Data decreases over time.
• Stationary trend: No clear increase or decrease.

Smoothing Data (Reducing Fluctuations)

• 3-point moving mean: Average of 3 consecutive values.
• 5-point moving mean: Average of 5 consecutive values.

Seasonal Indices (SI)

Formula:

Seasonal Index = Actual Value ÷ Trend Value

• SI > 1 → Above-average season.
• SI < 1 → Below-average season.

Deseasonalising Data

Formula:

Deseasonalised Value = Actual Value ÷ Seasonal Index

Regression Line (Trend Line)

Equation of the line:

y = mx + c

• m = gradient (rate of change).
• c = y-intercept (starting value).

Bivariate Data Analysis

Types of Correlation

• Positive → Both variables increase together.
• Negative

English Grammar Practice: Sentence Construction & Verb Usage

Choose the Correct Option: Quantifiers & General Usage

• I had many interesting experiences during that year.
• My dad has a lot of work.
• There isn’t enough space in this.
• I’ve been to this train station many times.
• There is a lot of competition between big supermarkets.

Complete the Sentences: Quantifiers & Context

• There is a flea market every Sunday.
• All my friends enjoy it.
• Many people drive, but few cycle.
• I’d rather travel on the train; there’s little choice and it's efficient.
• This is a pedestrian zone; no motor vehicles are allowed.
• I’ve been to Paris several times.
• There wasn’t much traffic.
• There is plenty to see.

Modal Verbs: Choose the Correct Option

• The lecturer must

Character & Conflict Analysis

Robinchon's Defeat by Marquis de Theremin

Question: How was Robinchon defeated by Marquis de Theremin? (4 marks)

Answer: Robinchon was defeated by the Marquis through a clever trick. The Marquis used his intelligence and experience to outwit Robinchon, exposing his lack of real knowledge and making him appear foolish in front of others. This resulted in Robinchon losing both credibility and respect.

Robinchon's Lecture at Apperville sous Bois

Question: What was the effect of Robinchon’s lecture at Apperville sous Bois? (2 marks)

Answer: Robinchon’s lecture left the audience unimpressed, leading to his humiliation.

Themes of Love & Sacrifice

Jim and Della: A Comparison to the Magi

Question: Why were Jim and Della... Continue reading "Literary & Historical Insights: Key Questions & Interpretations" »