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iv_tls_user_register, iv_tls_user_ptr - thread-local storage handling for ivykis

iv_tls(3) ivykis programmer's manual iv_tls(3)

NAME

iv_tls_user_register, iv_tls_user_ptr - thread-local storage handling for ivykis modules

SYNOPSIS

#include <iv_tls.h>
 
struct iv_tls_user {
        size_t          sizeof_state;
        void            (*init_thread)(void *st);
        void            (*deinit_thread)(void *st);
};
 
void iv_tls_user_register(struct iv_tls_user *tu);
 
void *iv_tls_user_ptr(const struct iv_tls_user *tu);
 

DESCRIPTION

The iv_tls interface provides thread-local storage handling to ivykis modules.
An ivykis module can arrange for an amount of memory to be allocated for its use in each ivykis thread by calling iv_tls_user_register. This must be done before any calls to iv_init have been made in this process, and is typically done from a module initialization function marked as a constructor function.
The ->sizeof_state member of the passed-in structure indicates how many bytes of memory the module wants allocated for its use in every ivykis thread.
When a thread calls iv_init, ->sizeof_state bytes of memory will be allocated for use by this module in that thread, and initialised to zero. A pointer to this memory area can be obtained by calling iv_tls_user_ptr (which returns NULL in non-ivykis threads).
If the specified ->init_thread function pointer is not NULL, it will be invoked at the end of iv_init, with its argument pointing to this thread's memory area allocation for this module.
If ->deinit_thread is not NULL, it will be invoked at the start of iv_deinit, or if the thread fails to call iv_deinit before terminating, at thread termination time. The argument passed into ->deinit_thread is the same as for ->init_thread.
It is permitted to call any ivykis API functions from the ->init_thread and ->deinit_thread callbacks.
There is no explicit serialization on calls to ->init_thread and ->deinit_thread.
Care must be taken when calling iv_tls_user_ptr from a signal handler, as there is a time window where it will return a non-NULL value before ->init_thread or after ->deinit_thread have been called.
Use of iv_tls for managing thread-local state is preferred over direct use of the __thread keyword, as not all platforms that ivykis runs on provide the __thread keyword.
Use of iv_tls for managing thread-local state is preferred over direct use of the pthread_key_create and pthread_setspecific APIs, as iv_tls provides a thread init hook as well as a destructor hook, and properly sequences ->init_thread and ->deinit_thread calls with core ivykis initialization and cleanup.

SEE ALSO

iv_init(3)
2012-03-30 ivykis