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docs: update double-checked locking

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Ilkka Seppälä
2024-05-25 15:36:05 +03:00
parent bf06bfc22a
commit 4e0382ca9f
1 changed files with 9 additions and 11 deletions
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double-checked-locking/README.md
+9 -11
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@@ -3,8 +3,10 @@ title: Double-Checked Locking
category: Concurrency category: Concurrency
language: en language: en
tag: tag:
- Lazy initialization
- Optimization - Optimization
- Performance - Performance
- Thread management
--- ---
## Intent ## Intent
@@ -27,9 +29,9 @@ Wikipedia says
**Programmatic Example** **Programmatic Example**
The Double-Checked Locking pattern is used in the HolderThreadSafe class to ensure that the Heavy object is only created once, even when accessed from multiple threads. Here's how it works: The Double-Checked Locking pattern is used in the `HolderThreadSafe` class to ensure that the `Heavy` object is only created once, even when accessed from multiple threads. Here's how it works:
Check if the object is initialized (first check): If it is, return it immediately. 1. Check if the object is initialized (first check): If it is, return it immediately.
```java ```java
if (heavy == null) { if (heavy == null) {
@@ -37,7 +39,7 @@ if (heavy == null) {
} }
``` ```
Synchronize the block of code where the object is created: This ensures that only one thread can create the object. 2. Synchronize the block of code where the object is created: This ensures that only one thread can create the object.
```java ```java
synchronized (this) { synchronized (this) {
@@ -45,7 +47,7 @@ synchronized (this) {
} }
``` ```
Check again if the object is initialized (second check): If another thread has already created the object by the time the current thread enters the synchronized block, return the created object. 3. Check again if the object is initialized. If another thread has already created the object by the time the current thread enters the synchronized block, return the created object.
```java ```java
if (heavy == null) { if (heavy == null) {
@@ -53,13 +55,13 @@ if (heavy == null) {
} }
``` ```
Return the created object. 4. Return the created object.
```java ```java
return heavy; return heavy;
``` ```
Here's the complete code for the HolderThreadSafe class: Here's the complete code for the `HolderThreadSafe` class:
```java ```java
public class HolderThreadSafe { public class HolderThreadSafe {
@@ -83,11 +85,7 @@ public class HolderThreadSafe {
} }
``` ```
In this code, the Heavy object is only created when the getHeavy() method is called for the first time. This is known as lazy initialization. The double-checked locking pattern is used to ensure that the Heavy object is only created once, even when the getHeavy() method is called from multiple threads simultaneously. In this code, the `Heavy` object is only created when the `getHeavy` method is called for the first time. This is known as lazy initialization. The double-checked locking pattern is used to ensure that the `Heavy` object is only created once, even when the `getHeavy` method is called from multiple threads simultaneously.
## Class diagram
![Double-Check Locking](./etc/double_checked_locking_1.png "Double-Checked Locking")
## Applicability ## Applicability