Doors is an

inter-process communication In computer science, inter-process communication or interprocess communication (IPC) refers specifically to the mechanisms an operating system provides to allow the processes to manage shared data. Typically, applications can use IPC, categori ...

facility for

Unix Unix (; trademarked as UNIX) is a family of multitasking, multiuser computer operating systems that derive from the original AT&T Unix, whose development started in 1969 at the Bell Labs research center by Ken Thompson, Dennis Ritchie, and ot ...

computer systems. They provide a form of

procedure call In computer programming, a function or subroutine is a sequence of program instructions that performs a specific task, packaged as a unit. This unit can then be used in programs wherever that particular task should be performed. Functions may ...

History

Doors were developed by

Sun Microsystems Sun Microsystems, Inc. (Sun for short) was an American technology company that sold computers, computer components, software, and information technology services and created the Java programming language, the Solaris operating system, ZFS, the ...

as a core part of the Spring operating system, then added to

Solaris Solaris may refer to: Arts and entertainment Literature, television and film * ''Solaris'' (novel), a 1961 science fiction novel by Stanisław Lem ** ''Solaris'' (1968 film), directed by Boris Nirenburg ** ''Solaris'' (1972 film), directed by ...

in version 2.5 as an undocumented internal interface. They became a documented feature in Solaris 2.6. Recent versions of Solaris use Doors in many places, including nscd (the

name service In computing, a directory service or name service maps the names of network resources to their respective network addresses. It is a shared information infrastructure for locating, managing, administering and organizing everyday items and network r ...

cache daemon) and

syslog In computing, syslog is a standard for message logging. It allows separation of the software that generates messages, the system that stores them, and the software that reports and analyzes them. Each message is labeled with a facility code, i ...

. A

Linux Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, which ...

port of Doors was released in 2003, but is only available for version 2.4.18.

Overview

The Doors subsystem is implemented as a

user-space A modern computer operating system usually segregates virtual memory into user space and kernel space. Primarily, this separation serves to provide memory protection and hardware protection from malicious or errant software behaviour. Kernel ...

library with some

kernel Kernel may refer to: Computing * Kernel (operating system), the central component of most operating systems * Kernel (image processing), a matrix used for image convolution * Compute kernel, in GPGPU programming * Kernel method, in machine learnin ...

support, and relies heavily on threads. It is designed for low overhead, and the Solaris implementation uses some assembly code for maximum efficiency. Doors are created by server processes (which must use threads) and called by client processes. It is possible for one process to both create and call a door. When creating a door, the server must specify a server procedure, which will be called by the Doors library on behalf of clients. Unlike most

remote procedure call In distributed computing, a remote procedure call (RPC) is when a computer program causes a procedure (subroutine) to execute in a different address space (commonly on another computer on a shared network), which is coded as if it were a normal (l ...

systems, each door has only one server procedure. A server can "attach" a door to a file, enabling clients to connect to that door simply by opening that file. The ls -l command will then show the file with a 'type' of "D" (not to be confused with "d" for a directory) — for example: Drw-r--r-- 1 jmorrison dev 876 Dec 8 19:43 myfile Clients use door_call() to invoke the door's server procedure, passing a contiguous region of memory and a list of

file descriptor In Unix and Unix-like computer operating systems, a file descriptor (FD, less frequently fildes) is a process-unique identifier (handle) for a file or other input/output resource, such as a pipe or network socket. File descriptors typically have ...

s as arguments, and getting back another contiguous region and list of file descriptors. Either region may be empty, as may either list. Usually, two C structs will be defined, one for the input data and one for the output data. (Alternatively,

tagged union In computer science, a tagged union, also called a variant, variant record, choice type, discriminated union, disjoint union, sum type or coproduct, is a data structure used to hold a value that could take on several different, but fixed, types. O ...

s may be used, allowing a door procedure to provide multiple actions in much the same way as the

ioctl In computing, ioctl (an abbreviation of input/output control) is a system call for device-specific input/output operations and other operations which cannot be expressed by regular system calls. It takes a parameter specifying a request code; th ...

system call.) Every file descriptor is accompanied by a flags word. The DOOR_RELEASE flag requests that a file descriptor be closed in the sending process after being duplicated in the receiving process. If a file descriptor that refers to a door is sent, the system records the properties of that door in the flags word. As well as representing a procedure, or a group of procedures, a door can represent a stateful data

object Object may refer to: General meanings * Object (philosophy), a thing, being, or concept ** Object (abstract), an object which does not exist at any particular time or place ** Physical object, an identifiable collection of matter * Goal, an ...

, making it possible to pass references to such objects between processes. Such a door would typically take a

as input data with each tag value denoting a different

method Method ( grc, μέθοδος, methodos) literally means a pursuit of knowledge, investigation, mode of prosecuting such inquiry, or system. In recent centuries it more often means a prescribed process for completing a task. It may refer to: *Scien ...

. The Doors system also provides a way for clients and servers to get information about each other. For example, a server can check the client's user or process ID to implement

access control In the fields of physical security and information security, access control (AC) is the selective restriction of access to a place or other resource, while access management describes the process. The act of ''accessing'' may mean consuming ...

. The Doors library normally creates and manages a pool of threads in the server process to handle calls, but it is possible to override this behavior. The Doors system does not provide any form of synchronization, but servers can use the normal thread-level synchronization primitives. Doors can be used to synchronize access to

shared memory In computer science, shared memory is memory that may be simultaneously accessed by multiple programs with an intent to provide communication among them or avoid redundant copies. Shared memory is an efficient means of passing data between progr ...

segments, allowing single-copy data transfer.http://developers.sun.com/solaris/articles/fastSockets.html The Doors concept is very similar to

X/Open X/Open group (also known as the Open Group for Unix Systems and incorporated in 1987 as X/Open Company, Ltd.) was a consortium founded by several European UNIX systems manufacturers in 1984 to identify and promote open standards in the field of info ...

XATMI API specification, where client processes invoke server processes' exposed functions: door_call() is analogous to tpcall() in XATMI clients, while door_return() is analogous to tpreturn() in XATMI servers.

References

External links

Solaris 10 man pages section 3: Realtime Library Functions
(

man pages A man page (short for manual page) is a form of software documentation usually found on a Unix or Unix-like operating system. Topics covered include computer programs (including library and system calls), formal standards and conventions, and ev ...

for the door-related functions) {{Solaris Sun Microsystems software Remote procedure call

History

Overview

See also

References

External links