Compare commits
1 Commits
master
...
revert-164
| Author | SHA1 | Date | |
|---|---|---|---|
|
8d36285549 |
@ -1,71 +0,0 @@
|
||||
---
|
||||
layout: pattern
|
||||
title: Monitor
|
||||
folder: monitor
|
||||
permalink: /patterns/monitor/
|
||||
categories: Concurrency
|
||||
language: en
|
||||
tags:
|
||||
- Performance
|
||||
---
|
||||
|
||||
## Intent
|
||||
Monitor pattern is used to create thread-safe objects and prevent conflicts between threads in concurrent applications.
|
||||
|
||||
## Explanation
|
||||
|
||||
In plain words
|
||||
|
||||
> Monitor pattern is used to enforce single-threaded access to data. Only one thread at a time is allowed to execute code within the monitor object.
|
||||
|
||||
Wikipedia says
|
||||
|
||||
> In concurrent programming (also known as parallel programming), a monitor is a synchronization construct that allows threads to have both mutual exclusion and the ability to wait (block) for a certain condition to become false. Monitors also have a mechanism for signaling other threads that their condition has been met.
|
||||
|
||||
**Programmatic Examples**
|
||||
|
||||
Consider there is a bank that transfers money from an account to another account with transfer method . it is `synchronized` mean just one thread can access to this method because if many threads access to it and transfer money from an account to another account in same time balance changed !
|
||||
|
||||
```
|
||||
class Bank {
|
||||
|
||||
private int[] accounts;
|
||||
Logger logger;
|
||||
|
||||
public Bank(int accountNum, int baseAmount, Logger logger) {
|
||||
this.logger = logger;
|
||||
accounts = new int[accountNum];
|
||||
Arrays.fill(accounts, baseAmount);
|
||||
}
|
||||
|
||||
public synchronized void transfer(int accountA, int accountB, int amount) {
|
||||
if (accounts[accountA] >= amount) {
|
||||
accounts[accountB] += amount;
|
||||
accounts[accountA] -= amount;
|
||||
logger.info("Transferred from account :" + accountA + " to account :" + accountB + " , amount :" + amount + " . balance :" + getBalance());
|
||||
}
|
||||
}
|
||||
```
|
||||
|
||||
getBalance always return total amount and the total amount should be same after each transfers
|
||||
|
||||
```
|
||||
private synchronized int getBalance() {
|
||||
int balance = 0;
|
||||
for (int account : accounts) {
|
||||
balance += account;
|
||||
}
|
||||
return balance;
|
||||
}
|
||||
}
|
||||
```
|
||||
|
||||
## Class diagram
|
||||
|
||||
|
||||
## Applicability
|
||||
Use the Monitor pattern when
|
||||
|
||||
* we have a shared resource and there is critical section .
|
||||
* you want to create thread-safe objects .
|
||||
* you want to achieve mutual exclusion in high level programming language .
|
||||
Binary file not shown.
|
Before Width: | Height: | Size: 10 KiB |
@ -1,12 +0,0 @@
|
||||
@startuml
|
||||
Main - Bank : use
|
||||
class Main{
|
||||
+ main(args : String[]) : void
|
||||
}
|
||||
class Bank{
|
||||
- accounts : int[]
|
||||
+ Bank (accountNum : int , baseAccount : int)
|
||||
+ transfer(accountA : int , accountB : int , amount : int) : void {synchronized}
|
||||
- getBalance() : void {synchronized}
|
||||
}
|
||||
@enduml
|
||||
@ -1,59 +0,0 @@
|
||||
<?xml version="1.0" encoding="UTF-8"?>
|
||||
<!--
|
||||
The MIT License
|
||||
Copyright © 2014-2021 Ilkka Seppälä
|
||||
Permission is hereby granted, free of charge, to any person obtaining a copy
|
||||
of this software and associated documentation files (the "Software"), to deal
|
||||
in the Software without restriction, including without limitation the rights
|
||||
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
|
||||
copies of the Software, and to permit persons to whom the Software is
|
||||
furnished to do so, subject to the following conditions:
|
||||
The above copyright notice and this permission notice shall be included in
|
||||
all copies or substantial portions of the Software.
|
||||
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
|
||||
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
|
||||
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
|
||||
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
|
||||
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
|
||||
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
|
||||
THE SOFTWARE.
|
||||
-->
|
||||
<project xmlns="http://maven.apache.org/POM/4.0.0"
|
||||
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
|
||||
xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
|
||||
<modelVersion>4.0.0</modelVersion>
|
||||
<parent>
|
||||
<artifactId>java-design-patterns</artifactId>
|
||||
<groupId>com.iluwatar</groupId>
|
||||
<version>1.24.0-SNAPSHOT</version>
|
||||
</parent>
|
||||
<artifactId>monitor</artifactId>
|
||||
<dependencies>
|
||||
<dependency>
|
||||
<groupId>org.junit.jupiter</groupId>
|
||||
<artifactId>junit-jupiter-engine</artifactId>
|
||||
<scope>test</scope>
|
||||
</dependency>
|
||||
</dependencies>
|
||||
<build>
|
||||
<plugins>
|
||||
<!-- Maven assembly plugin is invoked with default setting which we have
|
||||
in parent pom and specifying the class having main method -->
|
||||
<plugin>
|
||||
<groupId>org.apache.maven.plugins</groupId>
|
||||
<artifactId>maven-assembly-plugin</artifactId>
|
||||
<executions>
|
||||
<execution>
|
||||
<configuration>
|
||||
<archive>
|
||||
<manifest>
|
||||
<mainClass>com.iluwatar.abstractdocument.Main</mainClass>
|
||||
</manifest>
|
||||
</archive>
|
||||
</configuration>
|
||||
</execution>
|
||||
</executions>
|
||||
</plugin>
|
||||
</plugins>
|
||||
</build>
|
||||
</project>
|
||||
@ -1,37 +0,0 @@
|
||||
package com.iluwatar.monitor;
|
||||
|
||||
import java.util.Arrays;
|
||||
import java.util.logging.Logger;
|
||||
|
||||
// Bank class implements the Monitor pattern
|
||||
public class Bank {
|
||||
|
||||
private int[] accounts;
|
||||
Logger logger;
|
||||
|
||||
public Bank(int accountNum, int baseAmount, Logger logger) {
|
||||
this.logger = logger;
|
||||
accounts = new int[accountNum];
|
||||
Arrays.fill(accounts, baseAmount);
|
||||
}
|
||||
|
||||
public synchronized void transfer(int accountA, int accountB, int amount) {
|
||||
if (accounts[accountA] >= amount) {
|
||||
accounts[accountB] += amount;
|
||||
accounts[accountA] -= amount;
|
||||
logger.info("Transferred from account :" + accountA + " to account :" + accountB + " , amount :" + amount + " . balance :" + getBalance());
|
||||
}
|
||||
}
|
||||
|
||||
public synchronized int getBalance() {
|
||||
int balance = 0;
|
||||
for (int account : accounts) {
|
||||
balance += account;
|
||||
}
|
||||
return balance;
|
||||
}
|
||||
|
||||
public int[] getAccounts() {
|
||||
return accounts;
|
||||
}
|
||||
}
|
||||
@ -1,60 +0,0 @@
|
||||
/*
|
||||
* The MIT License
|
||||
* Copyright © 2014-2021 Ilkka Seppälä
|
||||
*
|
||||
* Permission is hereby granted, free of charge, to any person obtaining a copy
|
||||
* of this software and associated documentation files (the "Software"), to deal
|
||||
* in the Software without restriction, including without limitation the rights
|
||||
* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
|
||||
* copies of the Software, and to permit persons to whom the Software is
|
||||
* furnished to do so, subject to the following conditions:
|
||||
*
|
||||
* The above copyright notice and this permission notice shall be included in
|
||||
* all copies or substantial portions of the Software.
|
||||
*
|
||||
* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
|
||||
* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
|
||||
* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
|
||||
* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
|
||||
* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
|
||||
* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
|
||||
* THE SOFTWARE.
|
||||
*/
|
||||
|
||||
package com.iluwatar.monitor;
|
||||
|
||||
import java.util.*;
|
||||
import java.util.concurrent.ExecutorService;
|
||||
import java.util.concurrent.Executors;
|
||||
import java.util.logging.Logger;
|
||||
|
||||
/**
|
||||
* <p>The Monitor pattern is used in concurrent algorithms to achieve mutual exclusion.</p>
|
||||
*
|
||||
* <p>Bank is a simple class that transfers money from an account to another account using
|
||||
* {@link Bank#transfer}. It can also return the balance of the bank account stored in the bank.</p>
|
||||
*
|
||||
* <p>Main class uses ThreadPool to run threads that do transactions on the bank accounts.</p>
|
||||
*/
|
||||
|
||||
public class Main {
|
||||
|
||||
public static void main(String[] args) {
|
||||
Logger logger = Logger.getLogger("monitor");
|
||||
var bank = new Bank(4, 1000, logger);
|
||||
Runnable runnable = () -> {
|
||||
try {
|
||||
Thread.sleep((long) (Math.random() * 1000));
|
||||
Random random = new Random();
|
||||
for (int i = 0; i < 1000000; i++)
|
||||
bank.transfer(random.nextInt(4), random.nextInt(4), (int) (Math.random() * 1000));
|
||||
} catch (InterruptedException e) {
|
||||
logger.info(e.getMessage());
|
||||
}
|
||||
};
|
||||
ExecutorService executorService = Executors.newFixedThreadPool(5);
|
||||
for (int i = 0; i < 5; i++) {
|
||||
executorService.execute(runnable);
|
||||
}
|
||||
}
|
||||
}
|
||||
@ -1,55 +0,0 @@
|
||||
package com.iluwater.java;
|
||||
|
||||
import com.iluwatar.monitor.Bank;
|
||||
import org.junit.jupiter.api.AfterAll;
|
||||
import org.junit.jupiter.api.BeforeAll;
|
||||
import org.junit.jupiter.api.Test;
|
||||
|
||||
import static org.junit.jupiter.api.Assertions.*;
|
||||
import static org.junit.jupiter.api.Assumptions.*;
|
||||
|
||||
import java.util.logging.Logger;
|
||||
|
||||
public class BankTest {
|
||||
|
||||
private static Bank bank;
|
||||
private static final int ACCOUNT_NUM = 4;
|
||||
private static final int BASE_AMOUNT = 1000;
|
||||
private static final Logger LOGGER = Logger.getLogger("monitor");
|
||||
|
||||
@BeforeAll
|
||||
public static void Setup() {
|
||||
bank = new Bank(ACCOUNT_NUM, BASE_AMOUNT, LOGGER);
|
||||
}
|
||||
|
||||
@Test
|
||||
public void GetAccountHaveNotBeNull() {
|
||||
assertNotNull(bank.getAccounts());
|
||||
}
|
||||
|
||||
@Test
|
||||
public void LengthOfAccountsHaveToEqualsToAccountNumConstant() {
|
||||
assumeTrue(bank.getAccounts() != null);
|
||||
assertEquals(ACCOUNT_NUM, bank.getAccounts().length);
|
||||
}
|
||||
|
||||
@Test
|
||||
public void TransferMethodHaveToTransferAmountFromAnAccountToOtherAccount() {
|
||||
bank.transfer(0, 1, 1000);
|
||||
int accounts[] = bank.getAccounts();
|
||||
assertEquals(0, accounts[0]);
|
||||
assertEquals(2000, 2000);
|
||||
}
|
||||
|
||||
@Test
|
||||
public void BalanceHaveToBeOK() {
|
||||
assertEquals(4000, bank.getBalance());
|
||||
}
|
||||
|
||||
|
||||
@AfterAll
|
||||
public static void TearDown() {
|
||||
bank = null;
|
||||
}
|
||||
|
||||
}
|
||||
Loading…
x
Reference in New Issue
Block a user