前提
參考資料：
Unsafe介紹
在Oracle的Jdk8無法獲取到sun.misc包的源碼，想看此包的源碼可以直接下載openjdk，包的路徑是：
- openjdk-8u40-src-b25-10_feb_2015\openjdk\jdk\src\share\classes\sun\misc。
當然，不同的openjdk版本的根目錄(這里是openjdk-8u40-src-b25-10_feb_2015)不一定相同。sun.misc包含了低級（native硬件級別的原子操作）、不安全的操作集合。
Java無法直接訪問到操作系統底層（如系統硬件等)，為此Java使用native方法來擴展Java程序的功能。Unsafe類提供了硬件級別的原子操作，提供了一些繞開JVM的更底層功能，由此提高效率。本文的Unsafe類來源於openjdk-8u40-src-b25-10_feb_2015。
Unsafe的使用建議
建議先看這個知乎帖子第一樓R大的回答：為什么JUC中大量使用了sun.misc.Unsafe 這個類，但官方卻不建議開發者使用。
使用Unsafe要注意以下幾個問題：
- 1、Unsafe有可能在未來的Jdk版本移除或者不允許Java應用代碼使用，這一點可能導致使用了Unsafe的應用無法運行在高版本的Jdk。
- 2、Unsafe的不少方法中必須提供原始地址(內存地址)和被替換對象的地址，偏移量要自己計算，一旦出現問題就是JVM崩潰級別的異常，會導致整個JVM實例崩潰，表現為應用程序直接crash掉。
- 3、Unsafe提供的直接內存訪問的方法中使用的內存不受JVM管理(無法被GC)，需要手動管理，一旦出現疏忽很有可能成為內存泄漏的源頭。
暫時總結出以上三點問題。Unsafe在JUC(java.util.concurrent)包中大量使用(主要是CAS)，在netty中方便使用直接內存，還有一些高並發的交易系統為了提高CAS的效率也有可能直接使用到Unsafe。總而言之，Unsafe類是一把雙刃劍。
Unsafe詳解
Unsafe中一共有82個public native修飾的方法，還有幾十個基於這82個public native方法的其他方法。
初始化代碼
private static native void registerNatives();
static {
registerNatives();
sun.reflect.Reflection.registerMethodsToFilter(Unsafe.class, "getUnsafe");
}
private Unsafe() {}
private static final Unsafe theUnsafe = new Unsafe();
@CallerSensitive
public static Unsafe getUnsafe() {
Class<?> caller = Reflection.getCallerClass();
if (!VM.isSystemDomainLoader(caller.getClassLoader()))
throw new SecurityException("Unsafe");
return theUnsafe;
}
初始化的代碼主要包括調用JVM本地方法registerNatives()和sun.reflect.Reflection#registerMethodsToFilter。然后新建一個Unsafe實例命名為theUnsafe，通過靜態方法getUnsafe()獲取，獲取的時候需要做權限判斷。由此可見，Unsafe使用了單例設計(可見構造私有化了)。Unsafe類做了限制，如果是普通的調用的話，它會拋出一個SecurityException異常；只有由主類加載器(BootStrap classLoader)加載的類才能調用這個類中的方法。最簡單的使用方式是基於反射獲取Unsafe實例。
Field f = Unsafe.class.getDeclaredField("theUnsafe");
f.setAccessible(true);
Unsafe unsafe = (Unsafe) f.get(null);
類、對象和變量相關方法
主要包括類的非常規實例化、基於偏移地址獲取或者設置變量的值、基於偏移地址獲取或者設置數組元素的值等。
getObject
public native Object getObject(Object o, long offset);
通過給定的Java變量獲取引用值。這里實際上是獲取一個Java對象o中，獲取偏移地址為offset的屬性的值，此方法可以突破修飾符的抑制，也就是無視private、protected和default修飾符。類似的方法有getInt、getDouble等等。
putObject
public native void putObject(Object o, long offset, Object x);
將引用值存儲到給定的Java變量中。這里實際上是設置一個Java對象o中偏移地址為offset的屬性的值為x，此方法可以突破修飾符的抑制，也就是無視private、protected和default修飾符。類似的方法有putInt、putDouble等等。
getObjectVolatile
public native Object getObjectVolatile(Object o, long offset);
此方法和上面的getObject功能類似，不過附加了'volatile'加載語義，也就是強制從主存中獲取屬性值。類似的方法有getIntVolatile、getDoubleVolatile等等。這個方法要求被使用的屬性被volatile修飾，否則功能和getObject方法相同。
putObjectVolatile
public native void putObjectVolatile(Object o, long offset, Object x);
此方法和上面的putObject功能類似，不過附加了'volatile'加載語義，也就是設置值的時候強制(JMM會保證獲得鎖到釋放鎖之間所有對象的狀態更新都會在鎖被釋放之后)更新到主存，從而保證這些變更對其他線程是可見的。類似的方法有putIntVolatile、putDoubleVolatile等等。這個方法要求被使用的屬性被volatile修飾，否則功能和putObject方法相同。
putOrderedObject
public native void putOrderedObject(Object o, long offset, Object x);
設置o對象中offset偏移地址offset對應的Object型field的值為指定值x。這是一個有序或者有延遲的putObjectVolatile方法，並且不保證值的改變被其他線程立即看到。只有在field被volatile修飾並且期望被修改的時候使用才會生效。類似的方法有putOrderedInt和putOrderedLong。
staticFieldOffset
public native long staticFieldOffset(Field f);
返回給定的靜態屬性在它的類的存儲分配中的位置(偏移地址)。不要在這個偏移量上執行任何類型的算術運算，它只是一個被傳遞給不安全的堆內存訪問器的cookie。注意：這個方法僅僅針對靜態屬性，使用在非靜態屬性上會拋異常。下面源碼中的方法注釋估計有誤，staticFieldOffset和objectFieldOffset的注釋估計是對調了，為什么會出現這個問題無法考究。
objectFieldOffset
public native long objectFieldOffset(Field f);
返回給定的非靜態屬性在它的類的存儲分配中的位置(偏移地址)。不要在這個偏移量上執行任何類型的算術運算，它只是一個被傳遞給不安全的堆內存訪問器的cookie。注意：這個方法僅僅針對非靜態屬性，使用在靜態屬性上會拋異常。
staticFieldBase
public native Object staticFieldBase(Field f);
返回給定的靜態屬性的位置，配合staticFieldOffset方法使用。實際上，這個方法返回值就是靜態屬性所在的Class對象的一個內存快照。注釋中說到，此方法返回的Object有可能為null，它只是一個'cookie'而不是真實的對象，不要直接使用的它的實例中的獲取屬性和設置屬性的方法，它的作用只是方便調用上面提到的像getInt(Object,long)等等的任意方法。
shouldBeInitialized
public native boolean shouldBeInitialized(Class<?> c);
檢測給定的類是否需要初始化。通常需要使用在獲取一個類的靜態屬性的時候(因為一個類如果沒初始化，它的靜態屬性也不會初始化)。 此方法當且僅當ensureClassInitialized方法不生效的時候才返回false。
ensureClassInitialized
public native void ensureClassInitialized(Class<?> c);
檢測給定的類是否已經初始化。通常需要使用在獲取一個類的靜態屬性的時候(因為一個類如果沒初始化，它的靜態屬性也不會初始化)。
arrayBaseOffset
public native int arrayBaseOffset(Class<?> arrayClass);
返回數組類型的第一個元素的偏移地址(基礎偏移地址)。如果arrayIndexScale方法返回的比例因子不為0，你可以通過結合基礎偏移地址和比例因子訪問數組的所有元素。Unsafe中已經初始化了很多類似的常量如ARRAY_BOOLEAN_BASE_OFFSET等。
arrayIndexScale
public native int arrayIndexScale(Class<?> arrayClass);
返回數組類型的比例因子(其實就是數據中元素偏移地址的增量，因為數組中的元素的地址是連續的)。此方法不適用於數組類型為"narrow"類型的數組，"narrow"類型的數組類型使用此方法會返回0(這里narrow應該是狹義的意思，但是具體指哪些類型暫時不明確，筆者查了很多資料也沒找到結果)。Unsafe中已經初始化了很多類似的常量如ARRAY_BOOLEAN_INDEX_SCALE等。
defineClass
public native Class<?> defineClass(String name, byte[] b, int off, int len,ClassLoader loader,ProtectionDomain protectionDomain);
告訴JVM定義一個類，返回類實例，此方法會跳過JVM的所有安全檢查。默認情況下，ClassLoader(類加載器)和ProtectionDomain(保護域)實例應該來源於調用者。
defineAnonymousClass
public native Class<?> defineAnonymousClass(Class<?> hostClass, byte[] data, Object[] cpPatches);
這個方法的使用可以看R大的知乎回答：JVM crashes at libjvm.so，下面截取一點內容解釋此方法。
- 1、VM Anonymous Class可以看作一種模板機制，如果程序要動態生成很多結構相同、只是若干變量不同的類的話，可以先創建出一個包含占位符常量的正常類作為模板，然后利用
sun.misc.Unsafe#defineAnonymousClass()方法，傳入該類(host class，宿主類或者模板類)以及一個作為"constant pool path"的數組來替換指定的常量為任意值，結果得到的就是一個替換了常量的VM Anonymous Class。 - 2、VM Anonymous Class從VM的角度看是真正的"沒有名字"的，在構造出來之后只能通過
Unsafe#defineAnonymousClass()返回出來一個Class實例來進行反射操作。
還有其他幾點看以自行閱讀。這個方法雖然翻譯為"定義匿名類"，但是它所定義的類和實際的匿名類有點不相同，因此一般情況下我們不會用到此方法。在Jdk中lambda表達式相關的東西用到它，可以看InnerClassLambdaMetafactory這個類。
allocateInstance
public native Object allocateInstance(Class<?> cls) throws InstantiationException;
通過Class對象創建一個類的實例，不需要調用其構造函數、初始化代碼、JVM安全檢查等等。同時，它抑制修飾符檢測，也就是即使構造器是private修飾的也能通過此方法實例化。
內存管理
addressSize
public native int addressSize();
獲取本地指針的大小(單位是byte)，通常值為4或者8。常量ADDRESS_SIZE就是調用此方法。
pageSize
public native int pageSize();
獲取本地內存的頁數，此值為2的冪次方。
allocateMemory
public native long allocateMemory(long bytes);
分配一塊新的本地內存，通過bytes指定內存塊的大小(單位是byte)，返回新開辟的內存的地址。如果內存塊的內容不被初始化，那么它們一般會變成內存垃圾。生成的本機指針永遠不會為零，並將對所有值類型進行對齊。可以通過freeMemory方法釋放內存塊，或者通過reallocateMemory方法調整內存塊大小。bytes值為負數或者過大會拋出IllegalArgumentException異常，如果系統拒絕分配內存會拋出OutOfMemoryError異常。
reallocateMemory
public native long reallocateMemory(long address, long bytes);
通過指定的內存地址address重新調整本地內存塊的大小，調整后的內存塊大小通過bytes指定(單位為byte)。可以通過freeMemory方法釋放內存塊，或者通過reallocateMemory方法調整內存塊大小。bytes值為負數或者過大會拋出IllegalArgumentException異常，如果系統拒絕分配內存會拋出OutOfMemoryError異常。
setMemory
public native void setMemory(Object o, long offset, long bytes, byte value);
將給定內存塊中的所有字節設置為固定值(通常是0)。內存塊的地址由對象引用o和偏移地址共同決定，如果對象引用o為null，offset就是絕對地址。第三個參數就是內存塊的大小，如果使用allocateMemory進行內存開辟的話，這里的值應該和allocateMemory的參數一致。value就是設置的固定值，一般為0(這里可以參考netty的DirectByteBuffer)。一般而言，o為null，所有有個重載方法是public native void setMemory(long offset, long bytes, byte value);，等效於setMemory(null, long offset, long bytes, byte value);。
多線程同步
主要包括監視器鎖定、解鎖以及CAS相關的方法。
monitorEnter
public native void monitorEnter(Object o);
鎖定對象，必須通過monitorExit方法才能解鎖。此方法經過實驗是可以重入的，也就是可以多次調用，然后通過多次調用monitorExit進行解鎖。
monitorExit
public native void monitorExit(Object o);
解鎖對象，前提是對象必須已經調用monitorEnter進行加鎖，否則拋出IllegalMonitorStateException異常。
tryMonitorEnter
public native boolean tryMonitorEnter(Object o);
嘗試鎖定對象，如果加鎖成功返回true，否則返回false。必須通過monitorExit方法才能解鎖。
compareAndSwapObject
public final native boolean compareAndSwapObject(Object o, long offset, Object expected, Object x);
針對Object對象進行CAS操作。即是對應Java變量引用o，原子性地更新o中偏移地址為offset的屬性的值為x，當且僅的偏移地址為offset的屬性的當前值為expected才會更新成功返回true，否則返回false。
- o：目標Java變量引用。
- offset：目標Java變量中的目標屬性的偏移地址。
- expected：目標Java變量中的目標屬性的期望的當前值。
- x：目標Java變量中的目標屬性的目標更新值。
類似的方法有compareAndSwapInt和compareAndSwapLong，在Jdk8中基於CAS擴展出來的方法有getAndAddInt、getAndAddLong、getAndSetInt、getAndSetLong、getAndSetObject，它們的作用都是：通過CAS設置新的值，返回舊的值。
線程的掛起和恢復
unpark
public native void unpark(Object thread);
釋放被park創建的在一個線程上的阻塞。這個方法也可以被使用來終止一個先前調用park導致的阻塞。這個操作是不安全的，因此必須保證線程是存活的(thread has not been destroyed)。從Java代碼中判斷一個線程是否存活的是顯而易見的，但是從native代碼中這機會是不可能自動完成的。
park
public native void park(boolean isAbsolute, long time);
阻塞當前線程直到一個unpark方法出現(被調用)、一個用於unpark方法已經出現過(在此park方法調用之前已經調用過)、線程被中斷或者time時間到期(也就是阻塞超時)。在time非零的情況下，如果isAbsolute為true，time是相對於新紀元之后的毫秒，否則time表示納秒。這個方法執行時也可能不合理地返回(沒有具體原因)。並發包java.util.concurrent中的框架對線程的掛起操作被封裝在LockSupport類中，LockSupport類中有各種版本pack方法，但最終都調用了Unsafe#park()方法。
內存屏障
內存屏障相關的方法是在Jdk8添加的。內存屏障相關的知識可以先自行查閱。
loadFence
public native void loadFence();
在該方法之前的所有讀操作，一定在load屏障之前執行完成。
storeFence
public native void storeFence();
在該方法之前的所有寫操作，一定在store屏障之前執行完成
fullFence
public native void fullFence();
在該方法之前的所有讀寫操作，一定在full屏障之前執行完成，這個內存屏障相當於上面兩個(load屏障和store屏障)的合體功能。
其他
getLoadAverage
public native int getLoadAverage(double[] loadavg, int nelems);
獲取系統的平均負載值，loadavg這個double數組將會存放負載值的結果，nelems決定樣本數量，nelems只能取值為1到3，分別代表最近1、5、15分鍾內系統的平均負載。如果無法獲取系統的負載，此方法返回-1，否則返回獲取到的樣本數量(loadavg中有效的元素個數)。實驗中這個方法一直返回-1，其實完全可以使用JMX中的相關方法替代此方法。
throwException
public native void throwException(Throwable ee);
繞過檢測機制直接拋出異常。
Unsafe使用例子
驗證staticFieldOffset和objectFieldOffset
public class Main {
public static void main(String[] args) throws Exception {
Field theUnsafe = Unsafe.class.getDeclaredField("theUnsafe");
theUnsafe.setAccessible(true);
Unsafe unsafe = (Unsafe) theUnsafe.get(null);
Class<Person> personClass = Person.class;
Field name = personClass.getField("NAME");
Field age = personClass.getField("age");
try {
System.out.println("objectFieldOffset name -->" + unsafe.objectFieldOffset(name));
} catch (Exception e) {
System.out.println(e.getMessage());
}
try {
System.out.println("objectFieldOffset age -->" + unsafe.objectFieldOffset(age));
} catch (Exception e) {
System.out.println(e.getMessage());
}
try {
System.out.println("staticFieldOffset name -->" + unsafe.staticFieldOffset(name));
} catch (Exception e) {
System.out.println(e.getMessage());
}
try {
System.out.println("staticFieldOffset age -->" + unsafe.staticFieldOffset(age));
} catch (Exception e) {
System.out.println(e.getMessage());
}
}
}
@Data
public class Person {
public static String NAME = "doge";
public String age;
}
輸出結果：
java.lang.IllegalArgumentException
at sun.misc.Unsafe.objectFieldOffset(Native Method)
at org.throwable.unsafe.Main.main(Main.java:23)
java.lang.IllegalArgumentException
at sun.misc.Unsafe.staticFieldOffset(Native Method)
at org.throwable.unsafe.Main.main(Main.java:38)
objectFieldOffset age -->12
staticFieldOffset name -->104
輸出結果說明了staticFieldOffset只能使用在靜態屬性，objectFieldOffset只能使用在非靜態屬性。
不依賴Class直接獲取靜態屬性的值
public class Main2 {
public static void main(String[] args) throws Exception {
Field theUnsafe = Unsafe.class.getDeclaredField("theUnsafe");
theUnsafe.setAccessible(true);
Unsafe unsafe = (Unsafe) theUnsafe.get(null);
//這里必須預先實例化Person,否則它的靜態字段不會加載
Person person = new Person();
Class<?> personClass = person.getClass();
Field name = personClass.getField("NAME");
//注意，上面的Field實例是通過Class獲取的，但是下面的獲取靜態屬性的值沒有依賴到Class
System.out.println(unsafe.getObject(unsafe.staticFieldBase(name), unsafe.staticFieldOffset(name)));
}
}
@Data
public class Person {
public static String NAME = "doge";
public String age;
}
輸出結果：
doge
獲取類中的靜態屬性值，只依賴到Field的實例，剩余工作交給Unsafe的API。
java.nio.DirectByteBuffer
這個是JDK中使用直接內存的Buffer。可以查看它的構造函數如下：
DirectByteBuffer(int cap) { // package-private
super(-1, 0, cap, cap);
boolean pa = VM.isDirectMemoryPageAligned();
int ps = Bits.pageSize();
long size = Math.max(1L, (long)cap + (pa ? ps : 0));
Bits.reserveMemory(size, cap);
long base = 0;
try {
base = unsafe.allocateMemory(size); //使用Unsafe分配內存
} catch (OutOfMemoryError x) {
Bits.unreserveMemory(size, cap);
throw x;
}
//使用Unsafe設置內存固定值
unsafe.setMemory(base, size, (byte) 0);
if (pa && (base % ps != 0)) {
// Round up to page boundary
address = base + ps - (base & (ps - 1));
} else {
address = base;
}
cleaner = Cleaner.create(this, new Deallocator(base, size, cap));
att = null;
}
Unsafe源碼附錄
如果你不想下載openjdk的源碼，下面貼出Unsafe類的源碼，來自openjdk-8u40-src-b25-10_feb_2015：
package sun.misc;
import java.security.*;
import java.lang.reflect.*;
import sun.reflect.CallerSensitive;
import sun.reflect.Reflection;
/**
* A collection of methods for performing low-level, unsafe operations.
* Although the class and all methods are public, use of this class is
* limited because only trusted code can obtain instances of it.
*
* @author John R. Rose
* @see #getUnsafe
*/
public final class Unsafe {
private static native void registerNatives();
static {
registerNatives();
sun.reflect.Reflection.registerMethodsToFilter(Unsafe.class, "getUnsafe");
}
private Unsafe() {}
private static final Unsafe theUnsafe = new Unsafe();
/**
* Provides the caller with the capability of performing unsafe
* operations.
*
* <p> The returned <code>Unsafe</code> object should be carefully guarded
* by the caller, since it can be used to read and write data at arbitrary
* memory addresses. It must never be passed to untrusted code.
*
* <p> Most methods in this class are very low-level, and correspond to a
* small number of hardware instructions (on typical machines). Compilers
* are encouraged to optimize these methods accordingly.
*
* <p> Here is a suggested idiom for using unsafe operations:
*
* <blockquote><pre>
* class MyTrustedClass {
* private static final Unsafe unsafe = Unsafe.getUnsafe();
* ...
* private long myCountAddress = ...;
* public int getCount() { return unsafe.getByte(myCountAddress); }
* }
* </pre></blockquote>
*
* (It may assist compilers to make the local variable be
* <code>final</code>.)
*
* @exception SecurityException if a security manager exists and its
* <code>checkPropertiesAccess</code> method doesn't allow
* access to the system properties.
*/
@CallerSensitive
public static Unsafe getUnsafe() {
Class<?> caller = Reflection.getCallerClass();
if (!VM.isSystemDomainLoader(caller.getClassLoader()))
throw new SecurityException("Unsafe");
return theUnsafe;
}
/// peek and poke operations
/// (compilers should optimize these to memory ops)
// These work on object fields in the Java heap.
// They will not work on elements of packed arrays.
/**
* Fetches a value from a given Java variable.
* More specifically, fetches a field or array element within the given
* object <code>o</code> at the given offset, or (if <code>o</code> is
* null) from the memory address whose numerical value is the given
* offset.
* <p>
* The results are undefined unless one of the following cases is true:
* <ul>
* <li>The offset was obtained from {@link #objectFieldOffset} on
* the {@link java.lang.reflect.Field} of some Java field and the object
* referred to by <code>o</code> is of a class compatible with that
* field's class.
*
* <li>The offset and object reference <code>o</code> (either null or
* non-null) were both obtained via {@link #staticFieldOffset}
* and {@link #staticFieldBase} (respectively) from the
* reflective {@link Field} representation of some Java field.
*
* <li>The object referred to by <code>o</code> is an array, and the offset
* is an integer of the form <code>B+N*S</code>, where <code>N</code> is
* a valid index into the array, and <code>B</code> and <code>S</code> are
* the values obtained by {@link #arrayBaseOffset} and {@link
* #arrayIndexScale} (respectively) from the array's class. The value
* referred to is the <code>N</code><em>th</em> element of the array.
*
* </ul>
* <p>
* If one of the above cases is true, the call references a specific Java
* variable (field or array element). However, the results are undefined
* if that variable is not in fact of the type returned by this method.
* <p>
* This method refers to a variable by means of two parameters, and so
* it provides (in effect) a <em>double-register</em> addressing mode
* for Java variables. When the object reference is null, this method
* uses its offset as an absolute address. This is similar in operation
* to methods such as {@link #getInt(long)}, which provide (in effect) a
* <em>single-register</em> addressing mode for non-Java variables.
* However, because Java variables may have a different layout in memory
* from non-Java variables, programmers should not assume that these
* two addressing modes are ever equivalent. Also, programmers should
* remember that offsets from the double-register addressing mode cannot
* be portably confused with longs used in the single-register addressing
* mode.
*
* @param o Java heap object in which the variable resides, if any, else
* null
* @param offset indication of where the variable resides in a Java heap
* object, if any, else a memory address locating the variable
* statically
* @return the value fetched from the indicated Java variable
* @throws RuntimeException No defined exceptions are thrown, not even
* {@link NullPointerException}
*/
public native int getInt(Object o, long offset);
/**
* Stores a value into a given Java variable.
* <p>
* The first two parameters are interpreted exactly as with
* {@link #getInt(Object, long)} to refer to a specific
* Java variable (field or array element). The given value
* is stored into that variable.
* <p>
* The variable must be of the same type as the method
* parameter <code>x</code>.
*
* @param o Java heap object in which the variable resides, if any, else
* null
* @param offset indication of where the variable resides in a Java heap
* object, if any, else a memory address locating the variable
* statically
* @param x the value to store into the indicated Java variable
* @throws RuntimeException No defined exceptions are thrown, not even
* {@link NullPointerException}
*/
public native void putInt(Object o, long offset, int x);
/**
* Fetches a reference value from a given Java variable.
* @see #getInt(Object, long)
*/
public native Object getObject(Object o, long offset);
/**
* Stores a reference value into a given Java variable.
* <p>
* Unless the reference <code>x</code> being stored is either null
* or matches the field type, the results are undefined.
* If the reference <code>o</code> is non-null, car marks or
* other store barriers for that object (if the VM requires them)
* are updated.
* @see #putInt(Object, int, int)
*/
public native void putObject(Object o, long offset, Object x);
/** @see #getInt(Object, long) */
public native boolean getBoolean(Object o, long offset);
/** @see #putInt(Object, int, int) */
public native void putBoolean(Object o, long offset, boolean x);
/** @see #getInt(Object, long) */
public native byte getByte(Object o, long offset);
/** @see #putInt(Object, int, int) */
public native void putByte(Object o, long offset, byte x);
/** @see #getInt(Object, long) */
public native short getShort(Object o, long offset);
/** @see #putInt(Object, int, int) */
public native void putShort(Object o, long offset, short x);
/** @see #getInt(Object, long) */
public native char getChar(Object o, long offset);
/** @see #putInt(Object, int, int) */
public native void putChar(Object o, long offset, char x);
/** @see #getInt(Object, long) */
public native long getLong(Object o, long offset);
/** @see #putInt(Object, int, int) */
public native void putLong(Object o, long offset, long x);
/** @see #getInt(Object, long) */
public native float getFloat(Object o, long offset);
/** @see #putInt(Object, int, int) */
public native void putFloat(Object o, long offset, float x);
/** @see #getInt(Object, long) */
public native double getDouble(Object o, long offset);
/** @see #putInt(Object, int, int) */
public native void putDouble(Object o, long offset, double x);
/**
* This method, like all others with 32-bit offsets, was native
* in a previous release but is now a wrapper which simply casts
* the offset to a long value. It provides backward compatibility
* with bytecodes compiled against 1.4.
* @deprecated As of 1.4.1, cast the 32-bit offset argument to a long.
* See {@link #staticFieldOffset}.
*/
@Deprecated
public int getInt(Object o, int offset) {
return getInt(o, (long)offset);
}
/**
* @deprecated As of 1.4.1, cast the 32-bit offset argument to a long.
* See {@link #staticFieldOffset}.
*/
@Deprecated
public void putInt(Object o, int offset, int x) {
putInt(o, (long)offset, x);
}
/**
* @deprecated As of 1.4.1, cast the 32-bit offset argument to a long.
* See {@link #staticFieldOffset}.
*/
@Deprecated
public Object getObject(Object o, int offset) {
return getObject(o, (long)offset);
}
/**
* @deprecated As of 1.4.1, cast the 32-bit offset argument to a long.
* See {@link #staticFieldOffset}.
*/
@Deprecated
public void putObject(Object o, int offset, Object x) {
putObject(o, (long)offset, x);
}
/**
* @deprecated As of 1.4.1, cast the 32-bit offset argument to a long.
* See {@link #staticFieldOffset}.
*/
@Deprecated
public boolean getBoolean(Object o, int offset) {
return getBoolean(o, (long)offset);
}
/**
* @deprecated As of 1.4.1, cast the 32-bit offset argument to a long.
* See {@link #staticFieldOffset}.
*/
@Deprecated
public void putBoolean(Object o, int offset, boolean x) {
putBoolean(o, (long)offset, x);
}
/**
* @deprecated As of 1.4.1, cast the 32-bit offset argument to a long.
* See {@link #staticFieldOffset}.
*/
@Deprecated
public byte getByte(Object o, int offset) {
return getByte(o, (long)offset);
}
/**
* @deprecated As of 1.4.1, cast the 32-bit offset argument to a long.
* See {@link #staticFieldOffset}.
*/
@Deprecated
public void putByte(Object o, int offset, byte x) {
putByte(o, (long)offset, x);
}
/**
* @deprecated As of 1.4.1, cast the 32-bit offset argument to a long.
* See {@link #staticFieldOffset}.
*/
@Deprecated
public short getShort(Object o, int offset) {
return getShort(o, (long)offset);
}
/**
* @deprecated As of 1.4.1, cast the 32-bit offset argument to a long.
* See {@link #staticFieldOffset}.
*/
@Deprecated
public void putShort(Object o, int offset, short x) {
putShort(o, (long)offset, x);
}
/**
* @deprecated As of 1.4.1, cast the 32-bit offset argument to a long.
* See {@link #staticFieldOffset}.
*/
@Deprecated
public char getChar(Object o, int offset) {
return getChar(o, (long)offset);
}
/**
* @deprecated As of 1.4.1, cast the 32-bit offset argument to a long.
* See {@link #staticFieldOffset}.
*/
@Deprecated
public void putChar(Object o, int offset, char x) {
putChar(o, (long)offset, x);
}
/**
* @deprecated As of 1.4.1, cast the 32-bit offset argument to a long.
* See {@link #staticFieldOffset}.
*/
@Deprecated
public long getLong(Object o, int offset) {
return getLong(o, (long)offset);
}
/**
* @deprecated As of 1.4.1, cast the 32-bit offset argument to a long.
* See {@link #staticFieldOffset}.
*/
@Deprecated
public void putLong(Object o, int offset, long x) {
putLong(o, (long)offset, x);
}
/**
* @deprecated As of 1.4.1, cast the 32-bit offset argument to a long.
* See {@link #staticFieldOffset}.
*/
@Deprecated
public float getFloat(Object o, int offset) {
return getFloat(o, (long)offset);
}
/**
* @deprecated As of 1.4.1, cast the 32-bit offset argument to a long.
* See {@link #staticFieldOffset}.
*/
@Deprecated
public void putFloat(Object o, int offset, float x) {
putFloat(o, (long)offset, x);
}
/**
* @deprecated As of 1.4.1, cast the 32-bit offset argument to a long.
* See {@link #staticFieldOffset}.
*/
@Deprecated
public double getDouble(Object o, int offset) {
return getDouble(o, (long)offset);
}
/**
* @deprecated As of 1.4.1, cast the 32-bit offset argument to a long.
* See {@link #staticFieldOffset}.
*/
@Deprecated
public void putDouble(Object o, int offset, double x) {
putDouble(o, (long)offset, x);
}
// These work on values in the C heap.
/**
* Fetches a value from a given memory address. If the address is zero, or
* does not point into a block obtained from {@link #allocateMemory}, the
* results are undefined.
*
* @see #allocateMemory
*/
public native byte getByte(long address);
/**
* Stores a value into a given memory address. If the address is zero, or
* does not point into a block obtained from {@link #allocateMemory}, the
* results are undefined.
*
* @see #getByte(long)
*/
public native void putByte(long address, byte x);
/** @see #getByte(long) */
public native short getShort(long address);
/** @see #putByte(long, byte) */
public native void putShort(long address, short x);
/** @see #getByte(long) */
public native char getChar(long address);
/** @see #putByte(long, byte) */
public native void putChar(long address, char x);
/** @see #getByte(long) */
public native int getInt(long address);
/** @see #putByte(long, byte) */
public native void putInt(long address, int x);
/** @see #getByte(long) */
public native long getLong(long address);
/** @see #putByte(long, byte) */
public native void putLong(long address, long x);
/** @see #getByte(long) */
public native float getFloat(long address);
/** @see #putByte(long, byte) */
public native void putFloat(long address, float x);
/** @see #getByte(long) */
public native double getDouble(long address);
/** @see #putByte(long, byte) */
public native void putDouble(long address, double x);
/**
* Fetches a native pointer from a given memory address. If the address is
* zero, or does not point into a block obtained from {@link
* #allocateMemory}, the results are undefined.
*
* <p> If the native pointer is less than 64 bits wide, it is extended as
* an unsigned number to a Java long. The pointer may be indexed by any
* given byte offset, simply by adding that offset (as a simple integer) to
* the long representing the pointer. The number of bytes actually read
* from the target address maybe determined by consulting {@link
* #addressSize}.
*
* @see #allocateMemory
*/
public native long getAddress(long address);
/**
* Stores a native pointer into a given memory address. If the address is
* zero, or does not point into a block obtained from {@link
* #allocateMemory}, the results are undefined.
*
* <p> The number of bytes actually written at the target address maybe
* determined by consulting {@link #addressSize}.
*
* @see #getAddress(long)
*/
public native void putAddress(long address, long x);
/// wrappers for malloc, realloc, free:
/**
* Allocates a new block of native memory, of the given size in bytes. The
* contents of the memory are uninitialized; they will generally be
* garbage. The resulting native pointer will never be zero, and will be
* aligned for all value types. Dispose of this memory by calling {@link
* #freeMemory}, or resize it with {@link #reallocateMemory}.
*
* @throws IllegalArgumentException if the size is negative or too large
* for the native size_t type
*
* @throws OutOfMemoryError if the allocation is refused by the system
*
* @see #getByte(long)
* @see #putByte(long, byte)
*/
public native long allocateMemory(long bytes);
/**
* Resizes a new block of native memory, to the given size in bytes. The
* contents of the new block past the size of the old block are
* uninitialized; they will generally be garbage. The resulting native
* pointer will be zero if and only if the requested size is zero. The
* resulting native pointer will be aligned for all value types. Dispose
* of this memory by calling {@link #freeMemory}, or resize it with {@link
* #reallocateMemory}. The address passed to this method may be null, in
* which case an allocation will be performed.
*
* @throws IllegalArgumentException if the size is negative or too large
* for the native size_t type
*
* @throws OutOfMemoryError if the allocation is refused by the system
*
* @see #allocateMemory
*/
public native long reallocateMemory(long address, long bytes);
/**
* Sets all bytes in a given block of memory to a fixed value
* (usually zero).
*
* <p>This method determines a block's base address by means of two parameters,
* and so it provides (in effect) a <em>double-register</em> addressing mode,
* as discussed in {@link #getInt(Object,long)}. When the object reference is null,
* the offset supplies an absolute base address.
*
* <p>The stores are in coherent (atomic) units of a size determined
* by the address and length parameters. If the effective address and
* length are all even modulo 8, the stores take place in 'long' units.
* If the effective address and length are (resp.) even modulo 4 or 2,
* the stores take place in units of 'int' or 'short'.
*
* @since 1.7
*/
public native void setMemory(Object o, long offset, long bytes, byte value);
/**
* Sets all bytes in a given block of memory to a fixed value
* (usually zero). This provides a <em>single-register</em> addressing mode,
* as discussed in {@link #getInt(Object,long)}.
*
* <p>Equivalent to <code>setMemory(null, address, bytes, value)</code>.
*/
public void setMemory(long address, long bytes, byte value) {
setMemory(null, address, bytes, value);
}
/**
* Sets all bytes in a given block of memory to a copy of another
* block.
*
* <p>This method determines each block's base address by means of two parameters,
* and so it provides (in effect) a <em>double-register</em> addressing mode,
* as discussed in {@link #getInt(Object,long)}. When the object reference is null,
* the offset supplies an absolute base address.
*
* <p>The transfers are in coherent (atomic) units of a size determined
* by the address and length parameters. If the effective addresses and
* length are all even modulo 8, the transfer takes place in 'long' units.
* If the effective addresses and length are (resp.) even modulo 4 or 2,
* the transfer takes place in units of 'int' or 'short'.
*
* @since 1.7
*/
public native void copyMemory(Object srcBase, long srcOffset,
Object destBase, long destOffset,
long bytes);
/**
* Sets all bytes in a given block of memory to a copy of another
* block. This provides a <em>single-register</em> addressing mode,
* as discussed in {@link #getInt(Object,long)}.
*
* Equivalent to <code>copyMemory(null, srcAddress, null, destAddress, bytes)</code>.
*/
public void copyMemory(long srcAddress, long destAddress, long bytes) {
copyMemory(null, srcAddress, null, destAddress, bytes);
}
/**
* Disposes of a block of native memory, as obtained from {@link
* #allocateMemory} or {@link #reallocateMemory}. The address passed to
* this method may be null, in which case no action is taken.
*
* @see #allocateMemory
*/
public native void freeMemory(long address);
/// random queries
/**
* This constant differs from all results that will ever be returned from
* {@link #staticFieldOffset}, {@link #objectFieldOffset},
* or {@link #arrayBaseOffset}.
*/
public static final int INVALID_FIELD_OFFSET = -1;
/**
* Returns the offset of a field, truncated to 32 bits.
* This method is implemented as follows:
* <blockquote><pre>
* public int fieldOffset(Field f) {
* if (Modifier.isStatic(f.getModifiers()))
* return (int) staticFieldOffset(f);
* else
* return (int) objectFieldOffset(f);
* }
* </pre></blockquote>
* @deprecated As of 1.4.1, use {@link #staticFieldOffset} for static
* fields and {@link #objectFieldOffset} for non-static fields.
*/
@Deprecated
public int fieldOffset(Field f) {
if (Modifier.isStatic(f.getModifiers()))
return (int) staticFieldOffset(f);
else
return (int) objectFieldOffset(f);
}
/**
* Returns the base address for accessing some static field
* in the given class. This method is implemented as follows:
* <blockquote><pre>
* public Object staticFieldBase(Class c) {
* Field[] fields = c.getDeclaredFields();
* for (int i = 0; i < fields.length; i++) {
* if (Modifier.isStatic(fields[i].getModifiers())) {
* return staticFieldBase(fields[i]);
* }
* }
* return null;
* }
* </pre></blockquote>
* @deprecated As of 1.4.1, use {@link #staticFieldBase(Field)}
* to obtain the base pertaining to a specific {@link Field}.
* This method works only for JVMs which store all statics
* for a given class in one place.
*/
@Deprecated
public Object staticFieldBase(Class<?> c) {
Field[] fields = c.getDeclaredFields();
for (int i = 0; i < fields.length; i++) {
if (Modifier.isStatic(fields[i].getModifiers())) {
return staticFieldBase(fields[i]);
}
}
return null;
}
/**
* Report the location of a given field in the storage allocation of its
* class. Do not expect to perform any sort of arithmetic on this offset;
* it is just a cookie which is passed to the unsafe heap memory accessors.
*
* <p>Any given field will always have the same offset and base, and no
* two distinct fields of the same class will ever have the same offset
* and base.
*
* <p>As of 1.4.1, offsets for fields are represented as long values,
* although the Sun JVM does not use the most significant 32 bits.
* However, JVM implementations which store static fields at absolute
* addresses can use long offsets and null base pointers to express
* the field locations in a form usable by {@link #getInt(Object,long)}.
* Therefore, code which will be ported to such JVMs on 64-bit platforms
* must preserve all bits of static field offsets.
* @see #getInt(Object, long)
*/
public native long staticFieldOffset(Field f);
/**
* Report the location of a given static field, in conjunction with {@link
* #staticFieldBase}.
* <p>Do not expect to perform any sort of arithmetic on this offset;
* it is just a cookie which is passed to the unsafe heap memory accessors.
*
* <p>Any given field will always have the same offset, and no two distinct
* fields of the same class will ever have the same offset.
*
* <p>As of 1.4.1, offsets for fields are represented as long values,
* although the Sun JVM does not use the most significant 32 bits.
* It is hard to imagine a JVM technology which needs more than
* a few bits to encode an offset within a non-array object,
* However, for consistency with other methods in this class,
* this method reports its result as a long value.
* @see #getInt(Object, long)
*/
public native long objectFieldOffset(Field f);
/**
* Report the location of a given static field, in conjunction with {@link
* #staticFieldOffset}.
* <p>Fetch the base "Object", if any, with which static fields of the
* given class can be accessed via methods like {@link #getInt(Object,
* long)}. This value may be null. This value may refer to an object
* which is a "cookie", not guaranteed to be a real Object, and it should
* not be used in any way except as argument to the get and put routines in
* this class.
*/
public native Object staticFieldBase(Field f);
/**
* Detect if the given class may need to be initialized. This is often
* needed in conjunction with obtaining the static field base of a
* class.
* @return false only if a call to {@code ensureClassInitialized} would have no effect
*/
public native boolean shouldBeInitialized(Class<?> c);
/**
* Ensure the given class has been initialized. This is often
* needed in conjunction with obtaining the static field base of a
* class.
*/
public native void ensureClassInitialized(Class<?> c);
/**
* Report the offset of the first element in the storage allocation of a
* given array class. If {@link #arrayIndexScale} returns a non-zero value
* for the same class, you may use that scale factor, together with this
* base offset, to form new offsets to access elements of arrays of the
* given class.
*
* @see #getInt(Object, long)
* @see #putInt(Object, long, int)
*/
public native int arrayBaseOffset(Class<?> arrayClass);
/** The value of {@code arrayBaseOffset(boolean[].class)} */
public static final int ARRAY_BOOLEAN_BASE_OFFSET
= theUnsafe.arrayBaseOffset(boolean[].class);
/** The value of {@code arrayBaseOffset(byte[].class)} */
public static final int ARRAY_BYTE_BASE_OFFSET
= theUnsafe.arrayBaseOffset(byte[].class);
/** The value of {@code arrayBaseOffset(short[].class)} */
public static final int ARRAY_SHORT_BASE_OFFSET
= theUnsafe.arrayBaseOffset(short[].class);
/** The value of {@code arrayBaseOffset(char[].class)} */
public static final int ARRAY_CHAR_BASE_OFFSET
= theUnsafe.arrayBaseOffset(char[].class);
/** The value of {@code arrayBaseOffset(int[].class)} */
public static final int ARRAY_INT_BASE_OFFSET
= theUnsafe.arrayBaseOffset(int[].class);
/** The value of {@code arrayBaseOffset(long[].class)} */
public static final int ARRAY_LONG_BASE_OFFSET
= theUnsafe.arrayBaseOffset(long[].class);
/** The value of {@code arrayBaseOffset(float[].class)} */
public static final int ARRAY_FLOAT_BASE_OFFSET
= theUnsafe.arrayBaseOffset(float[].class);
/** The value of {@code arrayBaseOffset(double[].class)} */
public static final int ARRAY_DOUBLE_BASE_OFFSET
= theUnsafe.arrayBaseOffset(double[].class);
/** The value of {@code arrayBaseOffset(Object[].class)} */
public static final int ARRAY_OBJECT_BASE_OFFSET
= theUnsafe.arrayBaseOffset(Object[].class);
/**
* Report the scale factor for addressing elements in the storage
* allocation of a given array class. However, arrays of "narrow" types
* will generally not work properly with accessors like {@link
* #getByte(Object, int)}, so the scale factor for such classes is reported
* as zero.
*
* @see #arrayBaseOffset
* @see #getInt(Object, long)
* @see #putInt(Object, long, int)
*/
public native int arrayIndexScale(Class<?> arrayClass);
/** The value of {@code arrayIndexScale(boolean[].class)} */
public static final int ARRAY_BOOLEAN_INDEX_SCALE
= theUnsafe.arrayIndexScale(boolean[].class);
/** The value of {@code arrayIndexScale(byte[].class)} */
public static final int ARRAY_BYTE_INDEX_SCALE
= theUnsafe.arrayIndexScale(byte[].class);
/** The value of {@code arrayIndexScale(short[].class)} */
public static final int ARRAY_SHORT_INDEX_SCALE
= theUnsafe.arrayIndexScale(short[].class);
/** The value of {@code arrayIndexScale(char[].class)} */
public static final int ARRAY_CHAR_INDEX_SCALE
= theUnsafe.arrayIndexScale(char[].class);
/** The value of {@code arrayIndexScale(int[].class)} */
public static final int ARRAY_INT_INDEX_SCALE
= theUnsafe.arrayIndexScale(int[].class);
/** The value of {@code arrayIndexScale(long[].class)} */
public static final int ARRAY_LONG_INDEX_SCALE
= theUnsafe.arrayIndexScale(long[].class);
/** The value of {@code arrayIndexScale(float[].class)} */
public static final int ARRAY_FLOAT_INDEX_SCALE
= theUnsafe.arrayIndexScale(float[].class);
/** The value of {@code arrayIndexScale(double[].class)} */
public static final int ARRAY_DOUBLE_INDEX_SCALE
= theUnsafe.arrayIndexScale(double[].class);
/** The value of {@code arrayIndexScale(Object[].class)} */
public static final int ARRAY_OBJECT_INDEX_SCALE
= theUnsafe.arrayIndexScale(Object[].class);
/**
* Report the size in bytes of a native pointer, as stored via {@link
* #putAddress}. This value will be either 4 or 8. Note that the sizes of
* other primitive types (as stored in native memory blocks) is determined
* fully by their information content.
*/
public native int addressSize();
/** The value of {@code addressSize()} */
public static final int ADDRESS_SIZE = theUnsafe.addressSize();
/**
* Report the size in bytes of a native memory page (whatever that is).
* This value will always be a power of two.
*/
public native int pageSize();
/// random trusted operations from JNI:
/**
* Tell the VM to define a class, without security checks. By default, the
* class loader and protection domain come from the caller's class.
*/
public native Class<?> defineClass(String name, byte[] b, int off, int len,
ClassLoader loader,
ProtectionDomain protectionDomain);
/**
* Define a class but do not make it known to the class loader or system dictionary.
* <p>
* For each CP entry, the corresponding CP patch must either be null or have
* the a format that matches its tag:
* <ul>
* <li>Integer, Long, Float, Double: the corresponding wrapper object type from java.lang
* <li>Utf8: a string (must have suitable syntax if used as signature or name)
* <li>Class: any java.lang.Class object
* <li>String: any object (not just a java.lang.String)
* <li>InterfaceMethodRef: (NYI) a method handle to invoke on that call site's arguments
* </ul>
* @params hostClass context for linkage, access control, protection domain, and class loader
* @params data bytes of a class file
* @params cpPatches where non-null entries exist, they replace corresponding CP entries in data
*/
public native Class<?> defineAnonymousClass(Class<?> hostClass, byte[] data, Object[] cpPatches);
/** Allocate an instance but do not run any constructor.
Initializes the class if it has not yet been. */
public native Object allocateInstance(Class<?> cls)
throws InstantiationException;
/** Lock the object. It must get unlocked via {@link #monitorExit}. */
public native void monitorEnter(Object o);
/**
* Unlock the object. It must have been locked via {@link
* #monitorEnter}.
*/
public native void monitorExit(Object o);
/**
* Tries to lock the object. Returns true or false to indicate
* whether the lock succeeded. If it did, the object must be
* unlocked via {@link #monitorExit}.
*/
public native boolean tryMonitorEnter(Object o);
/** Throw the exception without telling the verifier. */
public native void throwException(Throwable ee);
/**
* Atomically update Java variable to <tt>x</tt> if it is currently
* holding <tt>expected</tt>.
* @return <tt>true</tt> if successful
*/
public final native boolean compareAndSwapObject(Object o, long offset,
Object expected,
Object x);
/**
* Atomically update Java variable to <tt>x</tt> if it is currently
* holding <tt>expected</tt>.
* @return <tt>true</tt> if successful
*/
public final native boolean compareAndSwapInt(Object o, long offset,
int expected,
int x);
/**
* Atomically update Java variable to <tt>x</tt> if it is currently
* holding <tt>expected</tt>.
* @return <tt>true</tt> if successful
*/
public final native boolean compareAndSwapLong(Object o, long offset,
long expected,
long x);
/**
* Fetches a reference value from a given Java variable, with volatile
* load semantics. Otherwise identical to {@link #getObject(Object, long)}
*/
public native Object getObjectVolatile(Object o, long offset);
/**
* Stores a reference value into a given Java variable, with
* volatile store semantics. Otherwise identical to {@link #putObject(Object, long, Object)}
*/
public native void putObjectVolatile(Object o, long offset, Object x);
/** Volatile version of {@link #getInt(Object, long)} */
public native int getIntVolatile(Object o, long offset);
/** Volatile version of {@link #putInt(Object, long, int)} */
public native void putIntVolatile(Object o, long offset, int x);
/** Volatile version of {@link #getBoolean(Object, long)} */
public native boolean getBooleanVolatile(Object o, long offset);
/** Volatile version of {@link #putBoolean(Object, long, boolean)} */
public native void putBooleanVolatile(Object o, long offset, boolean x);
/** Volatile version of {@link #getByte(Object, long)} */
public native byte getByteVolatile(Object o, long offset);
/** Volatile version of {@link #putByte(Object, long, byte)} */
public native void putByteVolatile(Object o, long offset, byte x);
/** Volatile version of {@link #getShort(Object, long)} */
public native short getShortVolatile(Object o, long offset);
/** Volatile version of {@link #putShort(Object, long, short)} */
public native void putShortVolatile(Object o, long offset, short x);
/** Volatile version of {@link #getChar(Object, long)} */
public native char getCharVolatile(Object o, long offset);
/** Volatile version of {@link #putChar(Object, long, char)} */
public native void putCharVolatile(Object o, long offset, char x);
/** Volatile version of {@link #getLong(Object, long)} */
public native long getLongVolatile(Object o, long offset);
/** Volatile version of {@link #putLong(Object, long, long)} */
public native void putLongVolatile(Object o, long offset, long x);
/** Volatile version of {@link #getFloat(Object, long)} */
public native float getFloatVolatile(Object o, long offset);
/** Volatile version of {@link #putFloat(Object, long, float)} */
public native void putFloatVolatile(Object o, long offset, float x);
/** Volatile version of {@link #getDouble(Object, long)} */
public native double getDoubleVolatile(Object o, long offset);
/** Volatile version of {@link #putDouble(Object, long, double)} */
public native void putDoubleVolatile(Object o, long offset, double x);
/**
* Version of {@link #putObjectVolatile(Object, long, Object)}
* that does not guarantee immediate visibility of the store to
* other threads. This method is generally only useful if the
* underlying field is a Java volatile (or if an array cell, one
* that is otherwise only accessed using volatile accesses).
*/
public native void putOrderedObject(Object o, long offset, Object x);
/** Ordered/Lazy version of {@link #putIntVolatile(Object, long, int)} */
public native void putOrderedInt(Object o, long offset, int x);
/** Ordered/Lazy version of {@link #putLongVolatile(Object, long, long)} */
public native void putOrderedLong(Object o, long offset, long x);
/**
* Unblock the given thread blocked on <tt>park</tt>, or, if it is
* not blocked, cause the subsequent call to <tt>park</tt> not to
* block. Note: this operation is "unsafe" solely because the
* caller must somehow ensure that the thread has not been
* destroyed. Nothing special is usually required to ensure this
* when called from Java (in which there will ordinarily be a live
* reference to the thread) but this is not nearly-automatically
* so when calling from native code.
* @param thread the thread to unpark.
*
*/
public native void unpark(Object thread);
/**
* Block current thread, returning when a balancing
* <tt>unpark</tt> occurs, or a balancing <tt>unpark</tt> has
* already occurred, or the thread is interrupted, or, if not
* absolute and time is not zero, the given time nanoseconds have
* elapsed, or if absolute, the given deadline in milliseconds
* since Epoch has passed, or spuriously (i.e., returning for no
* "reason"). Note: This operation is in the Unsafe class only
* because <tt>unpark</tt> is, so it would be strange to place it
* elsewhere.
*/
public native void park(boolean isAbsolute, long time);
/**
* Gets the load average in the system run queue assigned
* to the available processors averaged over various periods of time.
* This method retrieves the given <tt>nelem</tt> samples and
* assigns to the elements of the given <tt>loadavg</tt> array.
* The system imposes a maximum of 3 samples, representing
* averages over the last 1, 5, and 15 minutes, respectively.
*
* @params loadavg an array of double of size nelems
* @params nelems the number of samples to be retrieved and
* must be 1 to 3.
*
* @return the number of samples actually retrieved; or -1
* if the load average is unobtainable.
*/
public native int getLoadAverage(double[] loadavg, int nelems);
// The following contain CAS-based Java implementations used on
// platforms not supporting native instructions
/**
* Atomically adds the given value to the current value of a field
* or array element within the given object <code>o</code>
* at the given <code>offset</code>.
*
* @param o object/array to update the field/element in
* @param offset field/element offset
* @param delta the value to add
* @return the previous value
* @since 1.8
*/
public final int getAndAddInt(Object o, long offset, int delta) {
int v;
do {
v = getIntVolatile(o, offset);
} while (!compareAndSwapInt(o, offset, v, v + delta));
return v;
}
/**
* Atomically adds the given value to the current value of a field
* or array element within the given object <code>o</code>
* at the given <code>offset</code>.
*
* @param o object/array to update the field/element in
* @param offset field/element offset
* @param delta the value to add
* @return the previous value
* @since 1.8
*/
public final long getAndAddLong(Object o, long offset, long delta) {
long v;
do {
v = getLongVolatile(o, offset);
} while (!compareAndSwapLong(o, offset, v, v + delta));
return v;
}
/**
* Atomically exchanges the given value with the current value of
* a field or array element within the given object <code>o</code>
* at the given <code>offset</code>.
*
* @param o object/array to update the field/element in
* @param offset field/element offset
* @param newValue new value
* @return the previous value
* @since 1.8
*/
public final int getAndSetInt(Object o, long offset, int newValue) {
int v;
do {
v = getIntVolatile(o, offset);
} while (!compareAndSwapInt(o, offset, v, newValue));
return v;
}
/**
* Atomically exchanges the given value with the current value of
* a field or array element within the given object <code>o</code>
* at the given <code>offset</code>.
*
* @param o object/array to update the field/element in
* @param offset field/element offset
* @param newValue new value
* @return the previous value
* @since 1.8
*/
public final long getAndSetLong(Object o, long offset, long newValue) {
long v;
do {
v = getLongVolatile(o, offset);
} while (!compareAndSwapLong(o, offset, v, newValue));
return v;
}
/**
* Atomically exchanges the given reference value with the current
* reference value of a field or array element within the given
* object <code>o</code> at the given <code>offset</code>.
*
* @param o object/array to update the field/element in
* @param offset field/element offset
* @param newValue new value
* @return the previous value
* @since 1.8
*/
public final Object getAndSetObject(Object o, long offset, Object newValue) {
Object v;
do {
v = getObjectVolatile(o, offset);
} while (!compareAndSwapObject(o, offset, v, newValue));
return v;
}
/**
* Ensures lack of reordering of loads before the fence
* with loads or stores after the fence.
* @since 1.8
*/
public native void loadFence();
/**
* Ensures lack of reordering of stores before the fence
* with loads or stores after the fence.
* @since 1.8
*/
public native void storeFence();
/**
* Ensures lack of reordering of loads or stores before the fence
* with loads or stores after the fence.
* @since 1.8
*/
public native void fullFence();
/**
* Throws IllegalAccessError; for use by the VM.
* @since 1.8
*/
private static void throwIllegalAccessError() {
throw new IllegalAccessError();
}
}
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