我正在尝试在Linux机器上使用JNA发布到信号量。出于某种原因,即使对于这个简单的例子,我也总是收到 22 错误(无效参数(。在我的理解中,下面的代码不应该打开 POSIX 信号量,发布到它并再次关闭它吗?
public class Sample {
private static final int O_CREAT = 0x40;
public static void main(String[] args) throws Exception {
File notifier = new File("/tmp", "_test" + new Random().nextInt());
if (!notifier.isFile() && !notifier.createNewFile()) {
throw new IllegalStateException("Could not create notifier: " + notifier);
}
SempahoreLibrary library = Native.load("c", SempahoreLibrary.class);
Pointer semaphore = library.sem_open(notifier.getAbsolutePath(), O_CREAT, 666, 0);
try {
library.sem_post(semaphore);
} finally {
library.sem_close(semaphore);
}
}
interface SempahoreLibrary extends Library {
Pointer sem_open(String name, int flags, int mode, int value) throws LastErrorException;
int sem_post(Pointer pointer) throws LastErrorException;
int sem_close(Pointer pointer) throws LastErrorException;
}
}
我最初也无法让它与 JNR 一起使用(强烈建议使用 JNA(,并且感到好奇。用 C 编写它有所帮助。:)
C 端口上的 strace 清楚地表明您不必预先创建文件,并且然后将信号量"映射"到它。使用完整路径也是错误的,因为信号量在/dev/shm 中创建,"/"在路径螺钉中创建向上一切:
futex(0x7f731b1190d0, FUTEX_WAKE_PRIVATE, 2147483647) = 0
openat(AT_FDCWD, "/dev/shm/sem.sema", O_RDWR|O_NOFOLLOW) = 3
fstat(3, {st_mode=S_IFREG|0644, st_size=32, ...}) = 0
因此,您应该能够删除整个文件/路径创建,只需对 sem_open 中的信号量使用常规的非路径名。此外,文件模式应该是八进制的,并且您应该确保还加载 pthread 库 - 这是必需的。
下面是 C 语言中的一个工作示例:
// clang -Wall sema.c -lpthread
#include <fcntl.h>
#include <sys/stat.h>
#include <semaphore.h>
#include <stdio.h>
#include <stdlib.h>
#include <errno.h>
int main(int argc, char** argv)
{
sem_t* s = sem_open("notifier", O_CREAT, 0644, 0);
if (!s) {
perror("sem_open");
exit(errno);
}
printf("s: %pn", s);
sem_post(s);
int value = -1;
sem_getvalue(s, &value);
printf("value: %dn", value);
sem_wait(s);
sem_getvalue(s, &value);
printf("value: %dn", value);
sem_close(s);
exit(EXIT_SUCCESS);
}
下面是一个使用 JNR 的工作 Java 版本:
import jnr.ffi.LastError;
import jnr.ffi.LibraryLoader;
import jnr.ffi.Pointer;
import jnr.ffi.Runtime;
public class Semaphore
{
private static final int O_CREAT = 0x40;
public interface SempahoreLibrary
{
Pointer sem_open(String name, int flags, int mode, int value);
int sem_post(Pointer pointer);
int sem_close(Pointer pointer);
}
public static void main(String[] args) throws Exception
{
LibraryLoader<SempahoreLibrary> loader = LibraryLoader.create(SempahoreLibrary.class);
loader.library("c");
loader.library("pthread");
SempahoreLibrary library = loader.load();
jnr.ffi.Runtime runtime = Runtime.getRuntime(library);
Pointer semaphore = library.sem_open("notifier", O_CREAT, 0644, 0);
if (semaphore == null)
{
int errno = LastError.getLastError(runtime);
System.out.println("sem_open: " + errno);
System.exit(errno);
}
System.out.println("semaphore: " + Long.toHexString(semaphore.address()));
try
{
int error = library.sem_post(semaphore);
System.out.println("post: " + (error == 0 ? "OK" : LastError.getLastError(runtime)));
}
finally
{
int error = library.sem_close(semaphore);
System.out.println("close: " + (error == 0 ? "OK" : LastError.getLastError(runtime)));
}
}
}