接着上一篇文章: OSX系统下的gettid
由于jstack可以获取到线程的id，故我们可以查看jstack的源代码，看JDK是如何实现的。
os_bsd.cpp
// Information of current thread in variety of formats
pid_t os::Bsd::gettid() {
int retval = -1;
#ifdef __APPLE__ //XNU kernel
// despite the fact mach port is actually not a thread id use it
// instead of syscall(SYS_thread_selfid) as it certainly fits to u4
retval = ::pthread_mach_thread_np(::pthread_self());
guarantee(retval != 0, "just checking");
return retval;
#elif __FreeBSD__
retval = syscall(SYS_thr_self);
#elif __OpenBSD__
retval = syscall(SYS_getthrid);
#elif __NetBSD__
retval = (pid_t) syscall(SYS__lwp_self);
#endif
if (retval == -1) {
return getpid();
}
}
这里说的很清楚，OSX并不是调用的syscall(SYSthreadselfid)，上一篇文章中也试着调用了，但是结果和jstack不一样。
有了上面的代码，我们在OSX系统下获取线程id就变得非常简单了。
NativeThreadId.h
#ifndef NativeThreadId_H
#define NativeThreadId_H
extern "C" int getThreadId();
#endif
NativeThreadId.cpp
#include "NativeThreadId.h"
#include <pthread.h>
/**
* gcc -c NativeThreadId.cpp
* gcc -dynamiclib -o libNativeTest.dylib NativeTest.o
*/
int getThreadId() {
return pthread_mach_thread_np(pthread_self());
}
至于Java调用，我们可以用JNA，非常方便。
import com.sun.jna.Library;
import com.sun.jna.Native;
import com.sun.jna.Platform;
public class Threads {
static {
if (Platform.isMac()) {
System.load("libNativeThreadId.dylib");
}
}
private interface CLibrary extends Library {
int syscall(int api);
}
private interface MLibrary extends Library {
int getThreadId();
}
private static final int __NR_gettid = Platform.is64Bit() ? 186 : 224;
private static final Library INSTANCE = (Library) Native.loadLibrary(Platform.isMac() ? "NativeThreadId"
: (Platform.isWindows() ? "msvcrt" : "c"), Platform.isMac() ? MLibrary.class : CLibrary.class);
public static int getThreadId() {
System.out.println(INSTANCE);
if (Platform.isMac()) {
return ((MLibrary)INSTANCE).getThreadId();
} else {
return ((CLibrary)INSTANCE).syscall(__NR_gettid);
}
}
}
执行并与jstack比较，正确。