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)