Shulou(Shulou.com)06/01 Report--

This article mainly introduces the example analysis of struct binder_node, which is very detailed and has certain reference value. Friends who are interested must finish it!

Struct binder_node {

Int debug_id; / / used to help debug

/ / when the reference count of a Binder entity object changes from 0 to 1 or from 1 to 0, the Binder driver requests the corresponding

/ / the Service component increases or decreases its reference count. The Binder driver encapsulates the reference count modification into a class

Type / is a work item of type binder_node, which sets the value of member work to BINDER_WORK_NODE and sets the

/ / it is added to the todo queue of the corresponding process waiting for processing

Struct binder_work work

Union {

Struct rb_node rb_node

Struct hlist_node dead_node

}

/ / points to the host process, which uses a red-black tree to maintain all its internal Binder entity objects, each of which

/ / the member variable rb_node of the Binder entity object happens to be a node of the red-black tree. If the Binder entity object

If the host process of / / is dead, then the Binder entity object is saved in a full file through its member variable dead_node

/ / in the hash list of the bureau.

Struct binder_proc * proc

/ / an Binder entity object may be referenced by multiple Client components at the same time, so the Binder driver uses structures

/ / binder_ref to describe these reference relationships, and all references that reference the same Binder entity object are saved in the

/ / in a hash list. This hash list is described by the refs member of the Binder entity object, while the Binder driver passes

/ / after refs, you can know which Client components reference the same Binder entity object.

Struct hlist_head refs

Int internal_strong_refs; / / strong reference count describing Bidner entity objects

Int local_weak_refs; / / weak reference count describing Binder entity objects

Int local_strong_refs; / / strong reference count describing Bidner entity objects

Void _ _ user * ptr; / / describes the Service component in user space and points to the shadow object of Service

Void _ _ user * cookie; / / describes the address of the Service component in user space, pointing to the address of Service

/ / when the Binder entity object requests the Service to perform an operation, the strong / weak reference count of the Service is increased

/ / has_strong_ref and has_weak_ref are set to 1

/ / when Service completes the operation requested by Binder, the strong / weak reference count of the Service is decremented, and has_strong_ref and has_weak_ref are set to 0

/ / in the process of requesting Service to increase / decrease the strong / weak reference count, the Binder entity will set the

/ / pending_strong_ref or pending_weak_ref set 1

/ / when Service completes the increase / decrease of strong / weak reference count, the two member variables are set to 0.

Unsigned has_strong_ref:1

Unsigned pending_strong_ref:1

Unsigned has_weak_ref:1

Unsigned pending_weak_ref:1

/ / describes whether the Binder object is handling an asynchronous transaction. The Binder driver saves a transaction in the todo queue

/ / indicates that the thread will handle the transaction. Each transaction is associated with a Binder entity object, which is required to be associated with the Binder real

/ / the Service component corresponding to the body object processes the transaction in the specified thread. However, when the Binder driver finds that a transaction is different

/ / when you step into a transaction, it is saved in an asynchronous transaction queue of the target Binder entity object, which is

/ / is described by the member variable async_todo. Asynchronous transactions are defined as one-way interprocess communication requests, that is, no

/ / the request for interprocess communication to wait for a reply, as opposed to a synchronous transaction. Because there is no need to wait for an answer, the Binder driver just

/ / it is considered that the priority of asynchronous transaction is lower than that of synchronous transaction, which is represented by all asynchronism of a Binder entity object at the same time.

/ / at most one transaction is processed, and the rest are waiting in an asynchronous transaction queue, while synchronous transactions are not subject to this restriction.

Unsigned has_async_transaction:1

/ / describes whether Binder entity objects can receive interprocess communication data containing file descriptors. 1 indicates that it can be received, 0 table

/ / indicates that reception is prohibited. When the data sent by one process to another process contains a file descriptor, the Binder driver

/ / automatically opens the same file in the target process. For security reasons, Binder programs use this variable to prevent

/ / the source process opens the file in the target process.

Unsigned accept_fds:1

/ / indicates the processing thread (that is, the Server process) required by the Binder entity object when it processes requests from the Client process

The minimum thread priority that a thread in / / should have.

Unsigned min_priority:8

Struct list_head async_todo

}

The above is all the content of this article "sample Analysis of struct binder_node". Thank you for reading! Hope to share the content to help you, more related knowledge, welcome to follow the industry information channel!

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.