자바의 FileDescriptor 클래스의 native 메소드 내부 찾아보기

 

FileDescriptor의 native 메소드가 어떻게 리눅스와 윈도우에 포팅되었는지 확인한다.

 

1. 자바 소스

java.io.FileDescriptor.java

package java.io; public final class FileDescriptor { private int fd; private long handle; ….. public native void sync() throws SyncFailedException; /* This routine initializes JNI field offsets for the class */ private static native void initIDs(); private static native long set(int d); }

 

2, native 소스

jdk 6u 22  소스 - FileDescriptor_md.c

/* * @(#)FileDescriptor_md.c 1.4 10/03/23 * * Copyright (c) 2006, Oracle and/or its affiliates. All rights reserved. * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms. */ #include "jni.h" #include "jni_util.h" #include "jvm.h" #include "io_util.h" #include "jlong.h" #include "io_util_md.h" #include "java_io_FileDescriptor.h" /*******************************************************************/ /* BEGIN JNI ********* BEGIN JNI *********** BEGIN JNI ************/ /*******************************************************************/ /* field id for jint 'fd' in java.io.FileDescriptor */ jfieldID IO_fd_fdID; /* field id for jlong 'handle' in java.io.FileDescriptor */ jfieldID IO_handle_fdID; /************************************************************** * static methods to store field IDs in initializers */ JNIEXPORT void JNICALL Java_java_io_FileDescriptor_initIDs(JNIEnv *env, jclass fdClass) {     IO_fd_fdID = (*env)->GetFieldID(env, fdClass, "fd", "I");     IO_handle_fdID = (*env)->GetFieldID(env, fdClass, "handle", "J"); } JNIEXPORT jlong JNICALL Java_java_io_FileDescriptor_set(JNIEnv *env, jclass fdClass, jint fd) {     SET_HANDLE(fd); } /************************************************************** * File Descriptor */ JNIEXPORT void JNICALL Java_java_io_FileDescriptor_sync(JNIEnv *env, jobject this) {     FD fd = THIS_FD(this);     if (IO_Sync(fd) == -1) {         JNU_ThrowByName(env, "java/io/SyncFailedException", "sync failed");     } }

 

3. 윈도우 구현

윈도우에서는 SET_HANDLE과 IO_Sync을 다음과 같이 정의하였다.

src/windows/native/java/io/io_util_md.h 파일

SET_HANDLE 매크로에서 input,output,error에 값에 대한 GetStdHandle 함수를 사용한다. (http://msdn.microsoft.com/en-us/library/windows/desktop/ms683231(v=vs.85).aspx

JNIEXPORT int handleSync(jlong fd); /* * Setting the handle field in Java_java_io_FileDescriptor_set for * standard handles stdIn, stdOut, stdErr */ #define SET_HANDLE(fd) \ if (fd == 0) { \ return (jlong)GetStdHandle(STD_INPUT_HANDLE); \ } else if (fd == 1) { \ return (jlong)GetStdHandle(STD_OUTPUT_HANDLE); \ } else if (fd == 2) { \ return (jlong)GetStdHandle(STD_ERROR_HANDLE); \ } else { \ return (jlong)-1; \ } \ #define IO_Sync handleSync

src/windows/native/java/io/io_util_md.c 파일

결국 자바의 sync는 윈도우의 FlushFileBuffers(핸들값) 함수를 이용한다.  (http://msdn.microsoft.com/en-us/library/windows/desktop/aa364439(v=vs.85).aspx)

JNIEXPORT int handleSync(jlong fd) { /* * From the documentation: * * On Windows NT, the function FlushFileBuffers fails if hFile * is a handle to console output. That is because console * output is not buffered. The function returns FALSE, and * GetLastError returns ERROR_INVALID_HANDLE. * * On the other hand, on Win95, it returns without error. I cannot * assume that 0, 1, and 2 are console, because if someone closes * System.out and then opens a file, they might get file descriptor * 1. An error on *that* version of 1 should be reported, whereas * an error on System.out (which was the original 1) should be * ignored. So I use isatty() to ensure that such an error was due * to this bogosity, and if it was, I ignore the error. */ HANDLE handle = (HANDLE)fd; if (!FlushFileBuffers(handle)) { if (GetLastError() != ERROR_ACCESS_DENIED) { /* from winerror.h */ return -1; } } return 0; }

 

4. 리눅스 구현

src/sloaris/native/java/io/FileDescriptor_md.c

/* field id for jint 'fd' in java.io.FileDescriptor */ jfieldID IO_fd_fdID; /************************************************************** * static methods to store field ID's in initializers */ JNIEXPORT void JNICALL Java_java_io_FileDescriptor_initIDs(JNIEnv *env, jclass fdClass) {     IO_fd_fdID = (*env)->GetFieldID(env, fdClass, "fd", "I"); } /************************************************************** * File Descriptor */ JNIEXPORT void JNICALL Java_java_io_FileDescriptor_sync(JNIEnv *env, jobject this) {     int fd = (*env)->GetIntField(env, this, IO_fd_fdID);     if (JVM_Sync(fd) == -1) {     JNU_ThrowByName(env, "java/io/SyncFailedException", "sync failed");     }    }

 

src/solaris/native/java/io/io_util_md.h 파일

set_handle은 깔끔히 무시해준다.

/* * Route the routines through HPI */ #define IO_Sync JVM_Sync /* * On Solaris, the handle field is unused */ #define SET_HANDLE(fd) return (jlong)-1

 

hotspot/src/share/vm/prims/jvm.cpp 파일

JVM_LEAF(jint, JVM_Sync(jint fd))     JVMWrapper2("JVM_Sync (0x%x)", fd);     //%note jvm_r6     return hpi::fsync(fd); JVM_END

 

JVMWrapper2 매크로는 jvm.cpp에 정의되어 있다. 특별한 일은 하지 않는다.

#define JVMWrapper2(arg1, arg2) JVMCountWrapper(arg1); JVMTraceWrapper(arg1, arg2) #define JVMCountWrapper(arg) \ static JVMHistogramElement* e = new JVMHistogramElement(arg); \ if (e != NULL) e->increment_count(); // Due to bug in VC++, we need a NULL check here eventhough it should never happen! class JVMTraceWrapper : public StackObj { public: JVMTraceWrapper(const char* format, ...) {    if (TraceJVMCalls) {         va_list ap;         va_start(ap, format);         tty->print("JVM ");         tty->vprint_cr(format, ap);         va_end(ap);     } } };

hpi::fsync() 함수의 원형은 hotspot/src/share/vm/runtime/hpi.hpp, hotspot/src/share/vm/runtime/hpi.h 에 있다.

hotspot/src/share/vm/runtime/hpi.h

typedef struct {   char *         (*NativePath)(char *path);   int            (*FileType)(const char *path);   int            (*Open)(const char *name, int openMode, int filePerm);   int            (*Close)(int fd);   jlong          (*Seek)(int fd, jlong offset, int whence);   int            (*SetLength)(int fd, jlong length);   int            (*Sync)(int fd);   int            (*Available)(int fd, jlong *bytes);   size_t         (*Read)(int fd, void *buf, unsigned int nBytes);   size_t         (*Write)(int fd, const void *buf, unsigned int nBytes);   int            (*FileSizeFD)(int fd, jlong *size); } HPI_FileInterface;

 

hotspot/src/share/vm/runtime/hpi.cpp

// // C++ wrapper to HPI. // class hpi : AllStatic { static HPI_FileInterface* _file; static inline int fsync(int fd); HPIDECL(fsync, "fsync", _file, Sync, int, "%d", (int fd), ("fd = %d", fd), (fd)); } #define HPIDECL(name, names, intf, func, ret_type, ret_fmt, arg_type, arg_print, arg) \ inline ret_type hpi::name arg_type { \ if (TraceHPI) { \ tty->print("hpi::" names "("); \ tty->print arg_print ; \ tty->print(") = "); \ } \ ret_type result = (*intf->func) arg ; \ if (TraceHPI) { \ tty->print_cr(ret_fmt, result); \ } \ return result; \ }

 

hpi.c

static HPI_FileInterface hpi_file_interface = { sysNativePath, sysFileType, sysOpen, sysClose, sysSeek, sysSetLength, sysSync, sysAvailable, sysRead, sysWrite, sysFileSizeFD };

 

hpi_impl.h

int sysSync(int fd);

 

sys_api_td.c

int sysSync(int fd) { /* * XXX: Is fsync() interruptible by the interrupt method? * Is so, add the TSD, sigsetjmp()/longjmp() code here. * * This probably shouldn't be throwing an error and should * be a macro. */ int ret; if ((ret = fsync(fd)) == -1) { } return ret; }

 

리눅스의 sync 호출은 간단히 리눅스의 fsync 함수를 호출하는 효과와 동일하다.

 

마치며.

재미있는 것은 파일(file), 소켓(socket), 모니터(lock) 모두 jvm.cpp를 거쳐 hpi.hpp 로 내려오게 된다. 파일의 경우는 IO lock/unlock의 개념도 있고. 공부할 내용이 풍부하다..

이제 시간되는 대로 jvm 내용을 찾아 들어가면 될 것 같다.