.BR "l4_getid" " - returns thread id, thread group id and space id of a thread."
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.SH SYNOPSIS
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.nf
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.B #include
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.B #include
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.BI "int l4_getid(struct task_ids " "*ids" ");"
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.SH DESCRIPTION
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.BR "l4_getid() " "returns thread id, thread group id and space id of a thread in a " "struct task_ids " "structure, as shown below."
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.nf
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.B struct task_ids {
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.BI " int " "tid" "; /* Fully qualified thread id */"
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.BI " int " "spid" "; /* Address space id (local to container) */"
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.BI " int " "tgid" "; /* Thread group id (local, defined by userspace protocol) */"
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};
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.fi
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.in 7
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Every thread in the system has a thread id, space id and a thread group id associated with it. Each thread and space id is globally unique across the system. Thread group ids are available for grouping threads in arbitrary groups, via a user-defined protocol. A newly created thread may join an existing thread group or create a new group. This behaviour is defined by the thread's pager. Such a user-defined thread group allocation protocol may be useful for implementing groups of threads by higher level OS services.
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Even though both thread and space ids are globally unique across the system, there is an addressability difference between them. Each thread id is a fully qualified id, carrying its container id information with it. Upon a system call that targets a thread id, the system allows addressing threads that reside in other containers. In contrast, space ids are not fully qualified. They are local to a container, and any system call addressing a space id cannot target a space in another container. For thread ids,
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.BI "__cid("tid ")"
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macro extracts the Container ID information from the fully qualified thread id, whereas the
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.BI " __raw_tid("tid ")"
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macro provides the raw Thread ID, which omits the container ID information from the thread id. Such a raw ID still uniquely identifies the thread across containers, i.e. there is one such raw id per thread across the system.
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.SH FUTURE
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.BR "l4_getid() " "call is currently not subject to capability checking, as every thread has a natural right to discover their ids. In the future, it is possible that this system call is used for naming discovery for other addressable entities. If such a role is given to this call, it may also become subject to capability checking, as access control would prove beneficial over naming discovery services."
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.SH L4 USERSPACE LIBRARY
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.nf
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.B #include
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/*
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* Returns Thread ID of current thread
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*/
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.BI "static inline l4id_t self_tid(" "void" ")"
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.SH RETURN VALUE
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.BR "l4_getid()" " always succeeds with a return value of 0."
