...
This noncompliant code example synchronizes on a Boolean lock object.
| Code Block | ||
|---|---|---|
| ||
private final Boolean initialized = Boolean.FALSE;
public void doSomething() {
synchronized (initialized) {
// ...
}
}
|
...
This noncompliant code example locks on a boxed Integer object.
| Code Block | ||
|---|---|---|
| ||
int lock = 0;
private final Integer Lock = lock; // Boxed primitive Lock is shared
public void doSomething() {
synchronized (Lock) {
// ...
}
}
|
...
This compliant solution locks on a nonboxed Integer, using a variant of the private lock object idiom. The doSomething() method synchronizes using the intrinsic lock of the Integer instance, Lock.
| Code Block | ||
|---|---|---|
| ||
int lock = 0;
private final Integer Lock = new Integer(lock);
public void doSomething() {
synchronized (Lock) {
// ...
}
}
|
...
This noncompliant code example locks on an interned String object.
| Code Block | ||
|---|---|---|
| ||
private final String lock = new String("LOCK").intern();
public void doSomething() {
synchronized (lock) {
// ...
}
}
|
...
This noncompliant code example locks on a final String literal.
| Code Block | ||
|---|---|---|
| ||
// This bug was found in jetty-6.1.3 BoundedThreadPool
private final String lock = "LOCK";
public void doSomething() {
synchronized (lock) {
// ...
}
}
|
...
This compliant solution locks on a noninterned String instance.
| Code Block | ||
|---|---|---|
| ||
private final String lock = new String("LOCK");
public void doSomething() {
synchronized (lock) {
// ...
}
}
|
...
This compliant solution synchronizes on a private final lock object. This is one of the few cases in which a java.lang.Object instance is useful.
| Code Block | ||
|---|---|---|
| ||
private final Object lock = new Object();
public void doSomething() {
synchronized (lock) {
// ...
}
}
|
...
Some static analysis tools can detect violations of this rule.
| Tool | Version | Checker | Description | ||||||
|---|---|---|---|---|---|---|---|---|---|
| ThreadSafe |
| CCE_CC_REUSEDOBJ_SYNC | Implemented |
Bibliography
[API 2006] | Class String, Collections |
| |
Locking | |
Synchronization | |