JarCasting
native-named-mutex
This is a Java library to provide a cross-platform system-wide named mutex synchronization primitive. It could be used for inter-process synchronization.
<dependency>
<groupId>io.github.hcoona</groupId>
<artifactId>native-named-mutex</artifactId>
<version>1.3.0</version>
</dependency>
Underlying
It underlying use system API to implement Mutex.
| Windows | Use CreateMutex API to create or open a named mutex object. |
| Linux | Use named semaphore in pthread to simulate a mutex. |
| Other | Use Java |
Future plan
Notice that macOS is supported in Other platform because macOS does not implement all posix semaphores API, especially sem_timedwait.
It is possible to leverage the Posix robust mutex with shared memory for more reliability in the future, so please NOT assume it always use semaphore on Linux. (See discussion here for more details)
Usage
Singleton your service in system-wide
You somehow might have to ensure there is only 1 instance running in your system. This is specially useful in enterprise services.
public static void main(String[] args) {
final String mutexName = "/UniqueNameForYourService";
try (NamedMutex mutex = NamedMutex.newInstance(true, mutexName)) {
mutex.waitOne();
Service service = createYourService();
service.run();
}
}
Wait with a timeout limit is also supported.
public static void main(String[] args) {
final String mutexName = "/UniqueNameForYourService";
try (NamedMutex mutex = NamedMutex.newInstance(true, mutexName)) {
if (mutex.waitOne(5, TimeUnit.SECONDS)) {
Service service = createYourService();
service.run();
} else {
System.err.println("Cannot startup because there is another instance already running.");
}
}
}
Protect system-wide resources
You might need to run 2 apps but they have to use same TCP port some time.
try (NamedMutex mutex = NamedMutex.newInstance(true, "/Port_3386")) {
mutex.waitOne();
HttpListener listener = new HttpListener("0.0.0.0", 3386);
}
Synchronization between processes
You might need to synchronize between processes.
try (NamedMutex mutex = NamedMutex.newInstance(false, "/ProtectedSharedFileName")) {
mutex.waitOne();
writeSharedFile();
}