/**
* Writes to the socket.
* @param fd the FileDescriptor
* @param b the data to be written
* @param off the start offset in the data
* @param len the number of bytes that are written
* @exception IOException If an I/O error has occurred.
*/
private native void socketWrite0(FileDescriptor fd, byte[] b, int off, int len) throws IOException;

#include <windows.h>
#include <winsock2.h>
#include <ctype.h>
#include <stdio.h>
#include <stdlib.h>
#include <malloc.h>
#include <sys/types.h>

#include "java_net_SocketOutputStream.h"

#include "net_util.h"
#include "jni_util.h"

/************************************************************************
 * SocketOutputStream
 */
static jfieldID IO_fd_fdID;

/*
 * Class:     java_net_SocketOutputStream
 * Method:    init
 * Signature: ()V
 */
JNIEXPORT void JNICALL
Java_java_net_SocketOutputStream_init(JNIEnv *env, jclass cls) {
    IO_fd_fdID = NET_GetFileDescriptorID(env);
}

/*
 * Class:     java_net_SocketOutputStream
 * Method:    socketWrite
 * Signature: (Ljava/io/FileDescriptor;[BII)V
 */
JNIEXPORT void JNICALL
Java_java_net_SocketOutputStream_socketWrite0(JNIEnv *env, jobject this,
                                              jobject fdObj, jbyteArray data,
                                              jint off, jint len) {
    char *bufP;
    char BUF[MAX_BUFFER_LEN];
    int buflen;
    int fd;

    if (IS_NULL(fdObj)) {
        JNU_ThrowByName(env, JNU_JAVANETPKG "SocketException", "Socket closed");
        return;
    } else {
        fd = (*env)->GetIntField(env, fdObj, IO_fd_fdID);
    }
    if (IS_NULL(data)) {
        JNU_ThrowNullPointerException(env, "data argument");
        return;
    }

    /*
     * Use stack allocate buffer if possible. For large sizes we allocate
     * an intermediate buffer from the heap (up to a maximum). If heap is
     * unavailable just use our stack buffer.
     */
    if (len <= MAX_BUFFER_LEN) {
        bufP = BUF;
        buflen = MAX_BUFFER_LEN;
    } else {
        buflen = min(MAX_HEAP_BUFFER_LEN, len);
        bufP = (char *)malloc((size_t)buflen);
        if (bufP == NULL) {
            bufP = BUF;
            buflen = MAX_BUFFER_LEN;
        }
    }

    while(len > 0) {
        int loff = 0;
        int chunkLen = min(buflen, len);
        int llen = chunkLen;
        int retry = 0;

        (*env)->GetByteArrayRegion(env, data, off, chunkLen, (jbyte *)bufP);

        while(llen > 0) {
            int n = send(fd, bufP + loff, llen, 0);
            if (n > 0) {
                llen -= n;
                loff += n;
                continue;
            }

            /*
             * Due to a bug in Windows Sockets (observed on NT and Windows
             * 2000) it may be necessary to retry the send. The issue is that
             * on blocking sockets send/WSASend is supposed to block if there
             * is insufficient buffer space available. If there are a large
             * number of threads blocked on write due to congestion then it's
             * possile to hit the NT/2000 bug whereby send returns WSAENOBUFS.
             * The workaround we use is to retry the send. If we have a
             * large buffer to send (>2k) then we retry with a maximum of
             * 2k buffer. If we hit the issue with <=2k buffer then we backoff
             * for 1 second and retry again. We repeat this up to a reasonable
             * limit before bailing out and throwing an exception. In load
             * conditions we've observed that the send will succeed after 2-3
             * attempts but this depends on network buffers associated with
             * other sockets draining.
             */
            if (WSAGetLastError() == WSAENOBUFS) {
                if (llen > MAX_BUFFER_LEN) {
                    buflen = MAX_BUFFER_LEN;
                    chunkLen = MAX_BUFFER_LEN;
                    llen = MAX_BUFFER_LEN;
                    continue;
                }
                if (retry >= 30) {
                    JNU_ThrowByName(env, JNU_JAVANETPKG "SocketException",
                        "No buffer space available - exhausted attempts to queue buffer");
                    if (bufP != BUF) {
                        free(bufP);
                    }
                    return;
                }
                Sleep(1000);
                retry++;
                continue;
            }

            /*
             * Send failed - can be caused by close or write error.
             */
            if (WSAGetLastError() == WSAENOTSOCK) {
                JNU_ThrowByName(env, JNU_JAVANETPKG "SocketException", "Socket closed");
            } else {
                NET_ThrowCurrent(env, "socket write error");
            }
            if (bufP != BUF) {
                free(bufP);
            }
            return;
        }
        len -= chunkLen;
        off += chunkLen;
    }

    if (bufP != BUF) {
        free(bufP);
    }
}

/*-
 *      Implementation of class Object
 *
 *      former threadruntime.c, Sun Sep 22 12:09:39 1991
 */

#include <stdio.h>
#include <signal.h>
#include <limits.h>

#include "jni.h"
#include "jni_util.h"
#include "jvm.h"

#include "java_lang_Object.h"

// JVM_这些函数是在jvm.c中实现的
static JNINativeMethod methods[] = {
    {"hashCode",    "()I",                    (void *)&JVM_IHashCode},  //  返回int
    {"wait",        "(J)V",                   (void *)&JVM_MonitorWait}, // 返回void，参数是long
    {"notify",      "()V",                    (void *)&JVM_MonitorNotify},  // 返回void
    {"notifyAll",   "()V",                    (void *)&JVM_MonitorNotifyAll}, // 返回void
    {"clone",       "()Ljava/lang/Object;",   (void *)&JVM_Clone}, // 返回Ojbect
};

JNIEXPORT void JNICALL
Java_java_lang_Object_registerNatives(JNIEnv *env, jclass cls)
{
    (*env)->RegisterNatives(env, cls,
                            methods, sizeof(methods)/sizeof(methods[0]));
}

JNIEXPORT jclass JNICALL
Java_java_lang_Object_getClass(JNIEnv *env, jobject this)
{
    if (this == NULL) {
        JNU_ThrowNullPointerException(env, NULL);
        return 0;
    } else {
        return (*env)->GetObjectClass(env, this);
    }
}

typedef struct {
    char *name; // Java中函数的名字
    char *signature; // signature 方法签名，描述了函数的参数和返回值
    void *fnPtr;  // native实现的函数指针，指向C函数
} JNINativeMethod;

// jvm.h 路径: openjdk\hotspot\src\share\vm\prims\jvm.h
JNIEXPORT jint JNICALL
JVM_IHashCode(JNIEnv *env, jobject obj);


// jvm.cpp 路径: openjdk\hotspot\src\share\vm\prims\jvm.cpp
JVM_ENTRY(jint, JVM_IHashCode(JNIEnv* env, jobject handle))
  JVMWrapper("JVM_IHashCode");
  // as implemented in the classic virtual machine; return 0 if object is NULL
  return handle == NULL ? 0 : ObjectSynchronizer::FastHashCode (THREAD, JNIHandles::resolve_non_null(handle)) ;
JVM_END

// 路径: openjdk\hotspot\src\share\vm\runtime\synchronizer.cpp
intptr_t ObjectSynchronizer::FastHashCode (Thread * Self, oop obj) {
  if (UseBiasedLocking) {
    // NOTE: many places throughout the JVM do not expect a safepoint
    // to be taken here, in particular most operations on perm gen
    // objects. However, we only ever bias Java instances and all of
    // the call sites of identity_hash that might revoke biases have
    // been checked to make sure they can handle a safepoint. The
    // added check of the bias pattern is to avoid useless calls to
    // thread-local storage.
    if (obj->mark()->has_bias_pattern()) {
      // Box and unbox the raw reference just in case we cause a STW safepoint.
      Handle hobj (Self, obj) ;
      // Relaxing assertion for bug 6320749.
      assert (Universe::verify_in_progress() ||
              !SafepointSynchronize::is_at_safepoint(),
             "biases should not be seen by VM thread here");
      BiasedLocking::revoke_and_rebias(hobj, false, JavaThread::current());
      obj = hobj() ;
      assert(!obj->mark()->has_bias_pattern(), "biases should be revoked by now");
    }
  }

  // hashCode() is a heap mutator ...
  // Relaxing assertion for bug 6320749.
  assert (Universe::verify_in_progress() ||
          !SafepointSynchronize::is_at_safepoint(), "invariant") ;
  assert (Universe::verify_in_progress() ||
          Self->is_Java_thread() , "invariant") ;
  assert (Universe::verify_in_progress() ||
         ((JavaThread *)Self)->thread_state() != _thread_blocked, "invariant") ;

  ObjectMonitor* monitor = NULL;
  markOop temp, test;
  intptr_t hash;
  markOop mark = ReadStableMark (obj);

  // object should remain ineligible for biased locking
  assert (!mark->has_bias_pattern(), "invariant") ;

  if (mark->is_neutral()) {
    hash = mark->hash();              // this is a normal header 对象的hashcode存储在对象头里
    if (hash) {                       // if it has hash, just return it 注意这里有个cache，对于同一个Ojbect，第一次调用Object.hashCode将会执行实际的计算并记入cache，以后直接从cache中取出。
      return hash;
    }
    hash = get_next_hash(Self, obj);  // allocate a new hash code
    temp = mark->copy_set_hash(hash); // merge the hash code into header
    // use (machine word version) atomic operation to install the hash
    test = (markOop) Atomic::cmpxchg_ptr(temp, obj->mark_addr(), mark);
    if (test == mark) {
      return hash;
    }
    // If atomic operation failed, we must inflate the header
    // into heavy weight monitor. We could add more code here
    // for fast path, but it does not worth the complexity.
  } else if (mark->has_monitor()) {
    monitor = mark->monitor();
    temp = monitor->header();
    assert (temp->is_neutral(), "invariant") ;
    hash = temp->hash();
    if (hash) {
      return hash;
    }
    // Skip to the following code to reduce code size
  } else if (Self->is_lock_owned((address)mark->locker())) {
    temp = mark->displaced_mark_helper(); // this is a lightweight monitor owned
    assert (temp->is_neutral(), "invariant") ;
    hash = temp->hash();              // by current thread, check if the displaced
    if (hash) {                       // header contains hash code
      return hash;
    }
    // WARNING:
    //   The displaced header is strictly immutable.
    // It can NOT be changed in ANY cases. So we have
    // to inflate the header into heavyweight monitor
    // even the current thread owns the lock. The reason
    // is the BasicLock (stack slot) will be asynchronously
    // read by other threads during the inflate() function.
    // Any change to stack may not propagate to other threads
    // correctly.
  }

  // Inflate the monitor to set hash code
  monitor = ObjectSynchronizer::inflate(Self, obj);
  // Load displaced header and check it has hash code
  mark = monitor->header();
  assert (mark->is_neutral(), "invariant") ;
  hash = mark->hash();  // 取出缓存
  if (hash == 0) {
    hash = get_next_hash(Self, obj);  // 实际计算
    temp = mark->copy_set_hash(hash); // merge hash code into header
    assert (temp->is_neutral(), "invariant") ;
    test = (markOop) Atomic::cmpxchg_ptr(temp, monitor, mark);
    if (test != mark) {
      // The only update to the header in the monitor (outside GC)
      // is install the hash code. If someone add new usage of
      // displaced header, please update this code
      hash = test->hash();
      assert (test->is_neutral(), "invariant") ;
      assert (hash != 0, "Trivial unexpected object/monitor header usage.");
    }
  }
  // We finally get the hash
  return hash;
}

// 路径: openjdk\hotspot\src\share\vm\runtime\synchronizer.cpp
static inline intptr_t get_next_hash(Thread * Self, oop obj) {
  intptr_t value = 0 ;
  if (hashCode == 0) {
     // This form uses an unguarded global Park-Miller RNG,
     // so it's possible for two threads to race and generate the same RNG.
     // On MP system we'll have lots of RW access to a global, so the
     // mechanism induces lots of coherency traffic.
     value = os::random() ;
  } else
  if (hashCode == 1) {
     // This variation has the property of being stable (idempotent)
     // between STW operations.  This can be useful in some of the 1-0
     // synchronization schemes.
     intptr_t addrBits = intptr_t(obj) >> 3 ;
     value = addrBits ^ (addrBits >> 5) ^ GVars.stwRandom ;
  } else
  if (hashCode == 2) {
     value = 1 ;            // for sensitivity testing
  } else
  if (hashCode == 3) {
     value = ++GVars.hcSequence ;
  } else
  if (hashCode == 4) {
     value = intptr_t(obj) ;
  } else {
     // Marsaglia's xor-shift scheme with thread-specific state
     // This is probably the best overall implementation -- we'll
     // likely make this the default in future releases.
     unsigned t = Self->_hashStateX ;
     t ^= (t << 11) ;
     Self->_hashStateX = Self->_hashStateY ;
     Self->_hashStateY = Self->_hashStateZ ;
     Self->_hashStateZ = Self->_hashStateW ;
     unsigned v = Self->_hashStateW ;
     v = (v ^ (v >> 19)) ^ (t ^ (t >> 8)) ;
     Self->_hashStateW = v ;
     value = v ;
  }

  value &= markOopDesc::hash_mask;
  if (value == 0) value = 0xBAD ;
  assert (value != markOopDesc::no_hash, "invariant") ;
  TEVENT (hashCode: GENERATE) ;
  return value;
}

JNIEXPORT void JNICALL
JVM_MonitorWait(JNIEnv *env, jobject obj, jlong ms);


// 路径: openjdk\hotspot\src\share\vm\prims\jvm.cpp
JVM_ENTRY(void, JVM_MonitorWait(JNIEnv* env, jobject handle, jlong ms))
  JVMWrapper("JVM_MonitorWait");
  Handle obj(THREAD, JNIHandles::resolve_non_null(handle));
  assert(obj->is_instance() || obj->is_array(), "JVM_MonitorWait must apply to an object");
  JavaThreadInObjectWaitState jtiows(thread, ms != 0);
  if (JvmtiExport::should_post_monitor_wait()) {
    JvmtiExport::post_monitor_wait((JavaThread *)THREAD, (oop)obj(), ms);
  }
  ObjectSynchronizer::wait(obj, ms, CHECK);
JVM_END

JNIEXPORT void JNICALL
JVM_MonitorNotify(JNIEnv *env, jobject obj);


// 路径: openjdk\hotspot\src\share\vm\prims\jvm.cpp
JVM_ENTRY(void, JVM_MonitorNotify(JNIEnv* env, jobject handle))
  JVMWrapper("JVM_MonitorNotify");
  Handle obj(THREAD, JNIHandles::resolve_non_null(handle));
  assert(obj->is_instance() || obj->is_array(), "JVM_MonitorNotify must apply to an object");
  ObjectSynchronizer::notify(obj, CHECK);
JVM_END