src/java.base/unix/native/libnio/ch/UnixDispatcher.c

/*
 * Copyright (c) 2022, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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#include "nio.h"
#include "nio_util.h"

#include "sun_nio_ch_UnixDispatcher.h"

static int preCloseFD = -1;     /* File descriptor to which we dup other fd's
                                   before closing them for real */

static void closeFileDescriptor(JNIEnv *env, int fd) {
    if (fd != -1) {
        int result = close(fd);
        if (result < 0)
            JNU_ThrowIOExceptionWithLastError(env, "Close failed");
    }
}

JNIEXPORT void JNICALL
Java_sun_nio_ch_UnixDispatcher_init(JNIEnv *env, jclass clazz)
{
    int sp[2];
    if (socketpair(PF_UNIX, SOCK_STREAM, 0, sp) < 0) {
        JNU_ThrowIOExceptionWithLastError(env, "socketpair failed");
        return;
    }
    preCloseFD = sp[0];
    close(sp[1]);
}

JNIEXPORT void JNICALL
Java_sun_nio_ch_UnixDispatcher_close0(JNIEnv *env, jclass clazz, jobject fdo)
{
    jint fd = fdval(env, fdo);
    closeFileDescriptor(env, fd);
}

JNIEXPORT void JNICALL
Java_sun_nio_ch_UnixDispatcher_preClose0(JNIEnv *env, jclass clazz, jobject fdo)
{
    jint fd = fdval(env, fdo);
    if (preCloseFD >= 0) {
        if (dup2(preCloseFD, fd) < 0)
            JNU_ThrowIOExceptionWithLastError(env, "dup2 failed");
    }
}