Zookeeper C API Guide III (callback function) (GO)

Last Update:2016-11-23 Source: Internet

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2013-02-21 12:54 by Haippy, 9237 reading, 0 reviews, Favorites, compilation

Next to the Zookeeper C API Guide II (Monitoring (Wathes), basic constants and structure introduction), this article focuses on Zookeeper C APIs in the various callback functions.

Introduction to various callback functions in Zookeeper C API

Before you introduce the Zookeeper C API, let's start by introducing the prototypes of the various callback functions in the Zookeeper C API:

monitoring functions (watch function) prototypes

typedef void (*WATCHER_FN) (zhandle_t *zh, int type, int state, const char *path,void *watcherctx);

The individual parameters of the monitoring function prototype are explained as follows:

Zh	Zookeeper handle (handle)
Type	*The event type. One of the _event constants.**
State	*Connection status (connection state). The status value is one of the _state constants.**
Path	The path of the Znode node that triggered the monitoring event, and if NULL, the event type is Zoo_session_event
Watcherctx	Monitor contexts (watcher context).

Prototypes of other callback functions

There are several callback functions in Zookeeper that are used in asynchronous APIs (functions that typically start with zoo_a*), which are divided into the following types of callback functions that handle the return value type of an asynchronous function: Handling a callback function that returns a void type, handling a callback function that returns a STAT structure, Handles callback functions that return a string, handles callback functions that return data, handles callback functions that return a list of strings (a list of string), and handles callback functions that return a list of strings (a list of string) and a Stat structure, and a callback function that handles returning ACL information , respectively, as follows:

Processing callback function that returns void type typedef void (* void_completion_t) (int rc, const void *data);//Handle returning the STAT structure of the callback function typedef void (* STAT_CO mpletion_t) (int rc, const struct STAT *stat, const void *data); The callback function that handles the return string is typedef void (* string_completion_t) (int RC, const char *value, const void *data); callback function to process return data typedef void (* data_completion_t) (int RC, const char *value, int value_len, const struct STAT *stat, const v OID *data);  The callback function that processes the return string list (a list of string) typedef void (* strings_completion_t) (int rc, const struct String_vector *strings, const void *data);  The callback function that processes the return string list (a list of string) and the STAT structure at the same time typedef void (* strings_stat_completion_t) (int rc, const struct STRING_VECTOR *strings, const struct STAT *stat, const void *data); callback function for processing and returning ACL information typedef void (* acl_completion_t) (int rc, struct acl_vector *acl, struct Stat *stat, const void *data) ;

Here are some examples of the use of these callback functions:

Handling callback functions that return void types

typedef void (* void_completion_t) (int rc, const void *data)

This callback function is typically called when an asynchronous API call ends or the Zookeeper client loses a connection.

The error code returned by the asynchronous function call, the connection loss/timeout will trigger the prototype function (here refers to the callback function with the function prototype, the same as the same), and the error code is Zconnectionloss--the Zookeeper client and the server-side connection is lost, or Zoperationtimeout-The connection timed out, and data-related events trigger the invocation of the prototype function with the corresponding error code, as shown in the following (0-generation asynchronous function call succeeded)

Data

A pointer passed in by the caller, through which the caller can pass a custom parameter to the callback function , and the developer is responsible for the release of the memory that the pointer points to.

Handling callback functions that return a STAT structure

typedef void (* stat_completion_t) (int rc, const struct STAT *stat, const void *data)