As a case study of using Spring Global Lock from a Spring Cloud project speaker cited a project on developing a Web-based book store with an online payment gateway. This presentation by Mykhailo Brodskyi (Consultant, Engineering at GlobalLogic Kharkiv), was delivered at GlobalLogic Kharkiv Java Conference 2018 on June 10, 2018.

1. Real Case of Spring
Global Lock Usage
Maksym Voroniy
PhD, Software Architect, Consultant

2. Simple case
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3. Buying book. Analyst vision
- Select book
From big list pick 2-3 books
- Make Order
Provide payment attributes and send request to server
- Validate
Server have to check availability of all books in Store
- Complete transaction
Withdraw money and reduce number of available in Store
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4. 1: SelectBook
2: CreateOrder
2: Buy 4: Validate
5: Pay
5: RemovePosition
Server Store Bank
User
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5. Possible
implementation
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6. BookOrder:
payment
isbn
Naive implementation
Store:
amount
isbn
Payment:
amount
transaction
@Transactional // (!)
public void buyBooks(List<Book> books, Payment userPayment){
// Validate:
final String checkSql =
"SELECT 1 FROM Store WHERE isbn = ? AND amount > 1";
// Modify business entities
final String insertPaymentSql =
"INSERT INTO Payment (amount, transaction) VALUES ...";
final String insertOrderSql =
"INSERT INTO BookOrder (payment, isbn) VALUES ...";
final String updateStoreSql =
"UPDATE Store SET amount = amount -1 WHERE isbn = ?";
}
Read uncommitted | Read committed | SerializableIsolation layers:
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7. Better implementation
@Transactional
public void buyBooks(List<Book> books, Payment userPayment){
// Validate:
final String checkSql =
"SELECT 1 FROM Store WHERE isbn = ? AND amount > 1 FOR UPDATE";
// Modify business entities
final String insertPaymentSql =
"INSERT INTO Payment (amount, transaction) VALUES ...";
final String insertOrderSql =
"INSERT INTO BookOrder (payment, isbn) VALUES ...";
final String updateStoreSql =
"UPDATE Store SET amount = amount -1 WHERE isbn = ?";
}
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8. Analyze it…
- What if bank
confirmation take more
than 40 sec?
- What if Store, Order
management are
micro-services?
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9. Spring Cloud
goes to stage
9

10. Spring Global Lock
Sexy small code
@Autowired
private LockRegistry lockRegistry;
@Transactional
public void buyBooks2(List<Book> books, Payment userPayment){
Lock lock = lockRegistry.obtain(userPayment.getUserId());
lock.lock(); // lock.tryLock();
try{
doInsertAndUpdate();
} catch (InterruptedException e1){
//give up
Thread.currentThread().interrupt();
} finally{
lock.unlock();
}
}
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-integration</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.integration</groupId>
<artifactId>spring-integration-core</artifactId>
</dependency>
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11. BookOrder:
payment
isbn
Under the hood
Store:
amount
isbn
Payment:
amount
transaction
Lock:
when
key
version
- GemfireLockRegistry
- JdbcLockRegistry
- RedisLockRegistry
- PassThruLockRegistry
- ZookeeperLockRegistry
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12. Go to distributed environment
Broken code
Lock:
when
key
version
(c) by http://martin.kleppmann.com/2016/02/08/how-to-do-distributed-locking.html
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13. Go to distributed environment
Final code
Lock:
when
key
version
(c) by http://martin.kleppmann.com/2016/02/08/how-to-do-distributed-locking.html
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14. Spring Global Lock
Manage Expiration
@Autowired
private LockRegistry lockRegistry;
@Autowired
private ExpirableLockRegistry lockRegistry;
@Scheduled(fixedDelay=50000)
public void cleanObsolete(){
lockRegistry.expireUnusedOlderThan(50000);//that are not currently locked
}
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15. Global Lock Important use-case
Leader Election
LockRegistryLeaderInitiator:
- Uses global lock with
expiry,
- There will never be more
than one leader
- May occasionally be no
leader for short periods
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16. Summary
- Use in distributed
environment (microservices
for example);
- SQL DB is good and faster
alternative;
- NoSQL DB may not
+
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17. Summary
- Use in distributed
environment (microservices
for example);
- SQL DB is good and faster
alternative;
- NoSQL DB may not
- Timeouts matters
- Your code should
handle fail
- May slow down system
+ -
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18. Thank you!
maksym.voroniy@globallogic.com