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 ini‐
tialization and cleanup.
SEE ALSOiv_init(3)ivykis 2012-03-30 iv_tls(3)
