ChildProcess

Overview

The ChildProcess module provides APIs to manage child processes. You can call the APIs to create a native child process and establish an IPC channel between the parent and child processes to implement multi-process application development.

The created child process does not support the UI or the calling of context-related APIs. A maximum of 512 child processes can be started through this module and childProcessManager (non-SELF_FORK mode).

System capability: SystemCapability.Ability.AbilityRuntime.Core

Since: 12

Summary

Files

Name	Description
native_child_process.h	Declares the APIs used to create a native child process and establish an IPC channel between the parent and child processes. File to include: <AbilityKit/native_child_process.h> Library: libchild_process.so

Types

Name	Description
typedef enum Ability_NativeChildProcess_ErrCode Ability_NativeChildProcess_ErrCode	Defines an enum for the error codes used by the native child process module.
typedef void(* OH_Ability_OnNativeChildProcessStarted) (int errCode, OHIPCRemoteProxy *remoteProxy)	Defines a callback function for notifying the child process startup result.
typedef struct NativeChildProcess_Fd	Defines a struct for the file descriptor of a child process.
typedef struct NativeChildProcess_FdList	Defines a struct for the linked list of file descriptors of a child process.
typedef struct NativeChildProcess_Args	Defines a struct for the arguments used for starting a child process.

Enums

Name

Description

Ability_NativeChildProcess_ErrCode { NCP_NO_ERROR = 0, NCP_ERR_INVALID_PARAM = 401, NCP_ERR_NOT_SUPPORTED = 801, NCP_ERR_INTERNAL = 16000050, NCP_ERR_BUSY = 16010001, NCP_ERR_TIMEOUT = 16010002, NCP_ERR_SERVICE_ERROR = 16010003, NCP_ERR_MULTI_PROCESS_DISABLED = 16010004, NCP_ERR_ALREADY_IN_CHILD = 16010005, NCP_ERR_MAX_CHILD_PROCESSES_REACHED = 16010006, NCP_ERR_LIB_LOADING_FAILED = 16010007, NCP_ERR_CONNECTION_FAILED = 16010008 }

Enumerates the error codes used by the native child process module.

Functions

Name	Description
int OH_Ability_CreateNativeChildProcess (const char *libName, OH_Ability_OnNativeChildProcessStarted onProcessStarted)	Creates a child process, loads the specified dynamic library file, and returns the startup result asynchronously through a callback parameter. The callback notification is an independent thread. When implementing the callback function, pay attention to thread synchronization and do not perform time-consuming operations to avoid long-time blocking.

NOTE

Currently, only 2-in-1 devices are supported, and only one native child process can be started for a process.

Type Description

OH_Ability_OnNativeChildProcessStarted

typedef void (*OH_Ability_OnNativeChildProcessStarted)(int errCode, OHIPCRemoteProxy *remoteProxy)

Description

Defines a callback function for notifying the child process startup result.

Since: 12

Parameters

Name	Description
errCode	NCP_NO_ERROR - The child process is created successfully. NCP_ERR_LIB_LOADING_FAILED - Loading the dynamic library file fails or the necessary export function is not implemented in the dynamic library. NCP_ERR_CONNECTION_FAILED - The OnConnect method implemented in the dynamic library does not return a valid IPC stub pointer. For details, see Ability_NativeChildProcess_ErrCode.
remoteProxy	Pointer to the IPC object of the child process. If an exception occurs, the value may be nullptr. The pointer must be released by calling OH_IPCRemoteProxy_Destroy when it is no longer needed.

See

OH_Ability_CreateNativeChildProcess

OH_IPCRemoteProxy_Destroy

NativeChildProcess_Fd

typedef struct NativeChildProcess_Fd {
    char* fdName;
    int32_t fd;
    struct NativeChildProcess_Fd* next;
} NativeChildProcess_Fd;

Description

Defines a struct for the file descriptor of a child process.

Since: 13

Parameters

Name	Description
fdName	Pointer to the keyword of the file descriptor. A maximum of 20 characters are allowed.
fd	File descriptor handle.
next	Pointer to the next file descriptor.

NativeChildProcess_FdList

typedef struct NativeChildProcess_FdList {
    struct NativeChildProcess_Fd* head;
} NativeChildProcess_FdList;

Description

Defines a struct for the linked list of file descriptors of a child process. A maximum of 16 file descriptors are supported.

Since: 13

Parameters

Name	Description
head	First file descriptor record in the linked list. For details, see NativeChildProcess_FdList.

NativeChildProcess_Args

typedef struct NativeChildProcess_Args {
    char* entryParams;
    struct NativeChildProcess_FdList fdList;
} NativeChildProcess_Args;

Description

Defines a struct for the arguments used for starting a child process.

Since: 13

Parameters

Name	Description
entryParams	Pointer to the entry parameters. The size cannot exceed 150 KB.
fdList	Linked list of File descriptors. For details, see NativeChildProcess_FdList.

NativeChildProcess_Options

typedef struct NativeChildProcess_Options {
    NativeChildProcess_IsolationMode isolationMode;
    int64_t reserved;
} NativeChildProcess_Options;

Description

Defines a struct for the child process options.

Since: 13

Parameters

Name	Description
isolationMode	Process isolation mode. For details, see NativeChildProcess_IsolationMode.
reserved	Reserved field.

Enum Description

Ability_NativeChildProcess_ErrCode

enum Ability_NativeChildProcess_ErrCode

Description

Enumerates the error codes used by the native child process module.

Since: 12

Value	Description
NCP_NO_ERROR	Operation successful.
NCP_ERR_INVALID_PARAM	Invalid parameter.
NCP_ERR_NOT_SUPPORTED	Creating a native child process is not supported.
NCP_ERR_INTERNAL	Internal error.
NCP_ERR_BUSY	A new child process cannot be created during the startup of another native child process. You can try again after the child process is started.
NCP_ERR_TIMEOUT	Starting the native child process times out.
NCP_ERR_SERVICE_ERROR	Server error.
NCP_ERR_MULTI_PROCESS_DISABLED	The multi-process mode is disabled. A child process cannot be started.
NCP_ERR_ALREADY_IN_CHILD	A process cannot be created in a child process.
NCP_ERR_MAX_CHILD_PROCESSES_REACHED	The number of native child processes reaches the maximum.
NCP_ERR_LIB_LOADING_FAILED	The child process fails to load the dynamic library because the file does not exist or the corresponding method is not implemented or exported.
NCP_ERR_CONNECTION_FAILED	The child process fails to call the OnConnect method of the dynamic library. An invalid IPC object pointer may be returned.

NativeChildProcess_IsolationMode

enum NativeChildProcess_IsolationMode

Description

Enumerates the isolation modes of a child process.

Since: 13

Value	Description
NCP_ISOLATION_MODE_NORMAL	Normal mode. The child process shares the data sandbox and network environment with the main process.
NCP_ISOLATION_MODE_ISOLATED	Isolated mode. The child process does not share the data sandbox and network environment with the main process.

Function Description

OH_Ability_CreateNativeChildProcess

int OH_Ability_CreateNativeChildProcess (const char *libName, OH_Ability_OnNativeChildProcessStarted onProcessStarted)

Description

Creates a child process, loads the specified dynamic library file, and returns the startup result asynchronously through a callback parameter. The callback notification is an independent thread. When implementing the callback function, pay attention to thread synchronization and do not perform time-consuming operations to avoid long-time blocking.

The dynamic library specified must implement and export the following functions:

1. OHIPCRemoteStub* NativeChildProcess_OnConnect()
2. void NativeChildProcess_MainProc()

The processing logic sequence is shown in the following pseudocode:

Parent process:
1. OH_Ability_CreateNativeChildProcess(libName, onProcessStartedCallback)

Child process:
2. dlopen(libName)
3. dlsym("NativeChildProcess_OnConnect")
4. dlsym("NativeChildProcess_MainProc")
5. ipcRemote = NativeChildProcess_OnConnect()
6. NativeChildProcess_MainProc()

Parent process:
7. onProcessStartedCallback(ipcRemote, errCode)

Child process:
8. The child process exits after the NativeChildProcess_MainProc() function is returned.

NOTE

Currently, only 2-in-1 devices are supported, and only one native child process can be started for a process.

Since: 12

Parameters

Name	Description
libName	Pointer to the name of the dynamic library file loaded in the child process. The value cannot be nullptr.
onProcessStartedCallback	Pointer to the callback function for notifying the child process startup result. The value cannot be nullptr. For details, see OH_Ability_OnNativeChildProcessStarted.

Returns

Returns NCP_NO_ERROR if the operation is successful; returns an error code defined in Ability_NativeChildProcess_ErrCode otherwise.

OH_Ability_StartNativeChildProcess

Ability_NativeChildProcess_ErrCode OH_Ability_StartNativeChildProcess(
    const char* entry, NativeChildProcess_Args args,
    NativeChildProcess_Options options, int32_t *pid)

Description

Starts a native child process, loads the specified dynamic library file, and calls the entry function. Arguments can be passed to the child process. The ArkTS basic runtime environment cannot be created in the child process.

The specified dynamic library must implement and export the entry parameters of NativeChildProcess_Args. For details, see Native Child Process Development (C/C++) - Creating a Child Process That Supports Pass-by-Parameter.

NOTE

This function is valid only for 2-in-1 devices and tablets.

Since: 13

Parameters

Name	Description
entry	The symbol and entry function of the dynamic library called in the child process are separated by a colon (😃, for example, libentry.so:Main. The value cannot be a null pointer.
args	Arguments passed to the child process. For details, see NativeChildProcess_Args.
options	Startup configuration options of the child process. For details, see NativeChildProcess_Options.
pid	ID of the child process to start.

Returns

Returns NCP_NO_ERROR if the operation is successful; returns an error code defined in Ability_NativeChildProcess_ErrCode otherwise.