Android Binder驱动中binder_thread.pid区分线程的技术咨询

Great catch on this detail of the Binder driver! Let's break down what's happening here:

• The struct binder_thread is the core structure the Binder driver uses to track per-thread state for processes interacting with Binder. A key field here is pid, which gets set to current->pid — this is how the driver uniquely identifies individual threads within a Binder process.

• This pid field plays a critical role in the binder_get_thread function. When a thread tries to interact with Binder, this function first checks if the thread already exists in the process's thread red-black tree (proc->threads). It does this by traversing the tree and comparing the target thread's pid against existing nodes.

Here's the relevant code snippet you referenced, formatted for clarity:

static struct binder_thread *binder_get_thread(struct binder_proc *proc) {
    struct binder_thread *thread = NULL;
    struct rb_node *parent = NULL;
    struct rb_node **p = &proc->threads.rb_node;
    // ... rest of the traversal and comparison logic
}

In the unshown portion of the code, the driver will traverse the red-black tree using the p pointer, comparing each existing binder_thread's pid to current->pid. If a match is found, it returns that existing thread structure. If not, it allocates a new binder_thread, sets its pid to current->pid, inserts it into the red-black tree, and returns the new instance.

This design makes sense because the red-black tree allows efficient lookups, inserts, and deletes — perfect for managing potentially large numbers of threads interacting with Binder across the system.

内容的提问来源于stack exchange，提问作者mmmmar