Ashmem

java.lang.Object
- ohos.utils.Ashmem

```
public class Ashmem
extends Object
```
Provides methods related to the anonymous shared memory (Ashmem), including creating, closing, mapping, and unmapping the Ashmem, reading data from and writing data into the Ashmem, obtaining the Ashmem size, and setting protection for the Ashmem.
The Ashmem is created by a process. You can map the created Ashmem object to the current process to read and write data. Alternatively, you can transfer and map this Ashmem object to another process for data read and write. You need to ensure the timing sequence for concurrent read and write operations among multiple processes.

从以下版本开始:

3

字段概要

字段
限定符和类型	字段	说明
`static int`	`PROT_EXEC`	Indicates that data in the Ashmem object can be executed.
`static int`	`PROT_NONE`	Indicates that data in the Ashmem object cannot be read, written, or executed.
`static int`	`PROT_READ`	Indicates that data in the Ashmem object can be read.
`static int`	`PROT_WRITE`	Indicates that data in the Ashmem object can be written.

构造器概要

构造器
构造器说明

Ashmem(long nativeObject)

构造器
构造器	说明
`Ashmem(long nativeObject)`

方法概要

所有方法静态方法实例方法具体方法
限定符和类型	方法	说明
`void`	`closeAshmem()`	Closes this Ashmem.
`static Ashmem`	`createAshmem(String name, int size)`	Creates an Ashmem object based on the specified debugging name and memory size.
`static Ashmem`	`createAshmemFromExisting(long unwrappedNativeObject)`	Creates an Ashmem object by copying an existing Ashmem object.
`protected void`	`finalize()`	Called by the garbage collector on an object when garbage collection determines that there are no more references to the object.
`long`	`getAshmemIdentity()`	Acquires the identity of Ashmem object.
`int`	`getAShmemSize()`	Obtains the memory size of the Ashmem object.
`boolean`	`mapAshmem(int mapType)`	Maps the Ashmem object onto this process using a specified mapping type.
`boolean`	`mapReadAndWriteAShmem()`	Creates a read/write mapping between the Ashmem object and this process.
`boolean`	`mapReadOnlyAShmem()`	Creates a read-only mapping between the Ashmem object and this process.
`byte[]`	`readFromAShmem(int size, int offset)`	Reads data from the Ashmem object.
`boolean`	`setProtection(int protectionType)`	Sets the protection type for the Ashmem object.
`void`	`unmapAShmem()`	Unmaps the Ashmem object from this process.
`boolean`	`writeToAShmem(byte[] data, int size, int offset)`	Writes data into the Ashmem object.

从类继承的方法 java.lang.Object
clone, equals, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

- 字段详细资料
  - PROT_EXEC
```
public static final int PROT_EXEC
```
    Indicates that data in the Ashmem object can be executed.
    It can be used to set the protection or mapping type for the Ashmem object.
    
    从以下版本开始:
    
    3
    
    另请参阅:
    
    常量字段值
  - PROT_NONE
```
public static final int PROT_NONE
```
    Indicates that data in the Ashmem object cannot be read, written, or executed.
    It can be used to set the protection or mapping type for the Ashmem object.
    
    从以下版本开始:
    
    3
    
    另请参阅:
    
    常量字段值
  - PROT_READ
```
public static final int PROT_READ
```
    Indicates that data in the Ashmem object can be read.
    It can be used to set the protection or mapping type for the Ashmem object.
    
    从以下版本开始:
    
    3
    
    另请参阅:
    
    常量字段值
  - PROT_WRITE
```
public static final int PROT_WRITE
```
    Indicates that data in the Ashmem object can be written.
    It can be used to set the protection or mapping type for the Ashmem object.
    
    从以下版本开始:
    
    3
    
    另请参阅:
    
    常量字段值
- 构造器详细资料
  - Ashmem
```
public Ashmem(long nativeObject)
```
- 方法详细资料
  - createAshmem
```
public static Ashmem createAshmem(String name,
                                  int size)
```
    Creates an Ashmem object based on the specified debugging name and memory size.
    The debugging name is used only for querying information about this Ashmem when you check the memory mappings of the processes that have mapped onto this Ashmem.
    
    参数:
    
    name - Indicates the debugging name, which helps query the Ashmem information.
    
    size - Indicates the size of the Ashmem.
    
    返回:
    
    Returns the created Ashmem object; returns null if the creation fails.
    
    从以下版本开始:
    
    4
  - createAshmemFromExisting
```
public static Ashmem createAshmemFromExisting(long unwrappedNativeObject)
```
    Creates an Ashmem object by copying an existing Ashmem object.
    The two Ashmem objects point to the same shared memory area.
    
    参数:
    
    unwrappedNativeObject - Indicates the ID of the existing Ashmem object. You can obtain the ID using the getAshmemIdentity() method.
    
    返回:
    
    Returns the created Ashmem object.
    
    从以下版本开始:
    
    4
  - finalize
```
protected void finalize()
                 throws Throwable
```
    从类复制的说明: Object
    
    Called by the garbage collector on an object when garbage collection determines that there are no more references to the object. A subclass overrides the finalize method to dispose of system resources or to perform other cleanup.
    The general contract of finalize is that it is invoked if and when the Java™ virtual machine has determined that there is no longer any means by which this object can be accessed by any thread that has not yet died, except as a result of an action taken by the finalization of some other object or class which is ready to be finalized. The finalize method may take any action, including making this object available again to other threads; the usual purpose of finalize, however, is to perform cleanup actions before the object is irrevocably discarded. For example, the finalize method for an object that represents an input/output connection might perform explicit I/O transactions to break the connection before the object is permanently discarded.
    The finalize method of class Object performs no special action; it simply returns normally. Subclasses of Object may override this definition.
    The Java programming language does not guarantee which thread will invoke the finalize method for any given object. It is guaranteed, however, that the thread that invokes finalize will not be holding any user-visible synchronization locks when finalize is invoked. If an uncaught exception is thrown by the finalize method, the exception is ignored and finalization of that object terminates.
    After the finalize method has been invoked for an object, no further action is taken until the Java virtual machine has again determined that there is no longer any means by which this object can be accessed by any thread that has not yet died, including possible actions by other objects or classes which are ready to be finalized, at which point the object may be discarded.
    The finalize method is never invoked more than once by a Java virtual machine for any given object.
    Any exception thrown by the finalize method causes the finalization of this object to be halted, but is otherwise ignored.
    
    覆盖:
    
    finalize 在类中 Object
    
    抛出:
    
    Throwable - the Exception raised by this method
    
    另请参阅:
    
    WeakReference, PhantomReference
  - closeAshmem
```
public void closeAshmem()
```
    Closes this Ashmem.
    You must call this method to close the Ashmem object created via createAshmem(java.lang.String,int) in a timely manner if you no longer need it, to prevent memory leaks.
    
    从以下版本开始:
    
    3
  - mapAshmem
```
public boolean mapAshmem(int mapType)
```
    Maps the Ashmem object onto this process using a specified mapping type.
    Before reading and writing data using the Ashmem, you must call this method to map the Ashmem object onto this process. The mapping size is the total memory size of the Ashmem object, and the mapping starts from the start position of the Ashmem. The mapping type must be included in the protection types set for this Ashmem object.
    
    参数:
    
    mapType - Indicates the mapping type to use. The value is a bitwise ORed combination of PROT_READ (readable/unreadable), PROT_WRITE (writable/unwritable), PROT_EXEC (executable/unexecutable), or PROT_NONE.
    
    返回:
    
    Returns true if the mapping is successful; returns false otherwise.
    
    从以下版本开始:
    
    3
  - mapReadAndWriteAShmem
```
public boolean mapReadAndWriteAShmem()
```
    Creates a read/write mapping between the Ashmem object and this process.
    The mapping size is the total memory size of the Ashmem object, and the mapping starts from the start position of the Ashmem. When calling this method, ensure that the protection types of the Ashmem object include PROT_READ | PROT_WRITE.
    
    返回:
    
    Returns true if the mapping is successful; returns false otherwise.
    
    从以下版本开始:
    
    3
  - mapReadOnlyAShmem
```
public boolean mapReadOnlyAShmem()
```
    Creates a read-only mapping between the Ashmem object and this process.
    The mapping size is the total memory size of the Ashmem object, and the mapping starts from the start position of the Ashmem. When calling this method, ensure that the protection types of the Ashmem object include PROT_READ.
    
    返回:
    
    Returns true if the mapping is successful; returns false otherwise.
    
    从以下版本开始:
    
    3
  - unmapAShmem
```
public void unmapAShmem()
```
    Unmaps the Ashmem object from this process.
    After you finish using the Ashmem that has been mapped onto your process via mapAshmem(int), mapReadAndWriteAshmem, or mapReadOnlyAshmem, you must call this method to cancel the mapping to prevent memory leaks. You can create a mapping again if required.
    
    从以下版本开始:
    
    3
  - setProtection
```
public boolean setProtection(int protectionType)
```
    Sets the protection type for the Ashmem object.
    The protection type can only be added but not removed.
    Once the protection type is set, it will take effect for all mappings to the Ashmem object, regardless of whether the mappings are created before or after the protection type is set.
    
    参数:
    
    protectionType - Indicates the protection type to set. The value is a bitwise ORed combination of PROT_READ, PROT_WRITE, PROT_EXEC, or PROT_NONE.
    
    返回:
    
    Returns true if the setting is successful; returns false otherwise.
    
    从以下版本开始:
    
    3
  - getAShmemSize
```
public int getAShmemSize()
```
    Obtains the memory size of the Ashmem object.
    
    返回:
    
    Returns the memory size of the Ashmem object.
    
    从以下版本开始:
    
    3
  - writeToAShmem
```
public boolean writeToAShmem(byte[] data,
                             int size,
                             int offset)
```
    Writes data into the Ashmem object.
    You need to control the timing sequence for multi-process operations.
    Before calling this method, ensure that you have obtained the write permission for the Ashmem object and a write mapping to this Ashmem object has been created for your process.
    
    参数:
    
    data - Indicates the data to be written into the Ashmem object.
    
    size - Indicates the size of the data to write.
    
    offset - Indicates the start position in the Ashmem object to write data.
    
    返回:
    
    Returns true if data is successfully written; returns false in other scenarios, for example, data is written out of bounds or the write permission is not obtained.
    
    从以下版本开始:
    
    3
  - readFromAShmem
```
public byte[] readFromAShmem(int size,
                             int offset)
```
    Reads data from the Ashmem object.
    You need to control the timing sequence for multi-process operations.
    Before calling this method, ensure that you have obtained the read permission for the Ashmem object and a read mapping to this Ashmem object has been created for your process.
    
    参数:
    
    size - Indicates the size of the data to read.
    
    offset - Indicates the start position in the Ashmem object to read data.
    
    返回:
    
    Returns the read data.
    
    从以下版本开始:
    
    3
  - getAshmemIdentity
```
public long getAshmemIdentity()
```
    Acquires the identity of Ashmem object.
    
    返回:
    
    Returns the identity of the Ashmem object.
    
    从以下版本开始:
    
    3

类 Ashmem

字段概要

构造器概要

方法概要

从类继承的方法 java.lang.Object

字段详细资料

PROT_EXEC

PROT_NONE

PROT_READ

PROT_WRITE

构造器详细资料

Ashmem

方法详细资料

createAshmem

createAshmemFromExisting

finalize

closeAshmem

mapAshmem

mapReadAndWriteAShmem

mapReadOnlyAShmem

unmapAShmem

setProtection

getAShmemSize

writeToAShmem

readFromAShmem

getAshmemIdentity