Netscape Portable Runtime
Encyclopedia
In computing
, the Netscape portable runtime, or NSPR, a platform abstraction library, makes all operating system
s it supports appear the same to (for example) Mozilla
-style web-browsers. NSPR provides platform independence for non-GUI operating system
facilities. These facilities include:
Much of the library, and perhaps the overall thrust of it in the Gromit environment, provides the underpinnings of the Java virtual machine, more or less mapping the sys layer that Sun
defines for the porting
of the Java VM to various platforms. NSPR does go beyond that requirement in some areas, as it also functions as the platform-independent layer for most of the servers produced by Netscape
.
Some manufacturers expect and prefer that programmers restructure and perhaps even rewrite existing code in order to use the NSPR API
. NSPR does not have as a goal the provision of a platform for the porting into Netscape of externally developed code.
to various host environments. NSPR20, an effort started in 1996, built on that original idea, though very little remains of the original code. (The "20" in "NSPR20" does not mean "version 2.0" but rather "second generation".) Many of the concepts show reform, expansion, and maturation. NSPR may still function appropriately as the platform-dependent layer under Java, but it primarily serves in supporting client
s written entirely in C
or in C++
.
s feature prominently in NSPR. The software industry
's offering of threads lacks consistency. NSPR, while far from perfect, does provide a single API to which clients may program and expect reasonably consistent behavior. The operating systems provide everything from no concept of threading at all up to and including sophisticated, scalable and efficient implementations. NSPR makes as much use of what the systems offer as it can. NSPR aims to impose as little overhead
as possible in accessing those appropriate system features.
s as described by C. A. R. Hoare
in "Monitors: An operating system structuring concept", Communications of the ACM
, 17(10), October 1974 and then formalized by Xerox
' Mesa programming language
("Mesa Language Manual", J.G. Mitchell et al., Xerox PARC, CSL-79-3 (Apr 1979)). This mechanism provides the basic mutual exclusion (mutex) and thread notification facilities (condition variables) implemented by NSPR. Additionally, NSPR provides synchronization methods more suited for use by Java. The Java-like facilities include monitor reentrancy, implicit and tightly bound notification capabilities with the ability to associate the synchronization objects dynamically.
slightly augments the Berkeley sockets
model and allows arbitrary layering. The designers originally intended to export synchronous I/O methods only, relying on threads to provide the concurrency needed for complex applications. That method of operation remains preferred, though one can configure the network I/O channels as non-blocking in the traditional sense.
-centric network address object. While it does not define the object as opaque, the API provides methods that allow and encourage clients to treat the addresses as polymorphic
items. In this area NSPR aims to provide a migration path between IPv4
and IPv6
. To that end one can perform translations of ASCII
strings (DNS
names) into NSPR's network address structures, regardless of whether the addressing technology uses IPv4 or IPv6.
Interval timers are based on a free running, 32-bit, platform-dependent resolution timer. Such timers are normally used to specify timeouts on I/O, waiting on condition variables and other rudimentary thread scheduling. Since these timers have finite namespace and are free running, they can wrap at any time. NSPR does not provide an epoch, but expects clients to deal with that issue. The granularity of the timers is guaranteed to be between 10 microseconds and 1 millisecond. This allows a minimal timer period in of approximately 12 hours. But in order to deal with the wrap-around issue, only half that namespace may be utilized. Therefore, the minimal usable interval available from the timers is slightly less than six hours.
Calendar times are 64-bit signed numbers with units of microseconds. The epoch for calendar times is midnight, January 1, 1970, Greenwich Mean Time
. Negative times extend to times before 1970, and positive numbers forward. Use of 64 bits allows a representation of times approximately in the range of −30000 to the year 30000. There exits a structural representation (i.e., exploded view), routines to acquire the current time from the host system, and convert them to and from the 64-bit and structural representation. Additionally there are routines to convert to and from most well-known forms of ASCII into the 64-bit NSPR representation.
, calloc, realloc and free functions. Depending on the platform, the functions may be implemented almost entirely in the NSPR runtime or simply shims that call immediately into the host operating system's offerings.
Computing
Computing is usually defined as the activity of using and improving computer hardware and software. It is the computer-specific part of information technology...
, the Netscape portable runtime, or NSPR, a platform abstraction library, makes all operating system
Operating system
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
s it supports appear the same to (for example) Mozilla
Mozilla
Mozilla is a term used in a number of ways in relation to the Mozilla.org project and the Mozilla Foundation, their defunct commercial predecessor Netscape Communications Corporation, and their related application software....
-style web-browsers. NSPR provides platform independence for non-GUI operating system
Operating system
An operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
facilities. These facilities include:
- threadThread (computer science)In computer science, a thread of execution is the smallest unit of processing that can be scheduled by an operating system. The implementation of threads and processes differs from one operating system to another, but in most cases, a thread is contained inside a process...
s - thread synchronization
- normal file and network I/O
- interval timing and calendar time
- basic memory managementMemory managementMemory management is the act of managing computer memory. The essential requirement of memory management is to provide ways to dynamically allocate portions of memory to programs at their request, and freeing it for reuse when no longer needed. This is critical to the computer system.Several...
(mallocMallocC dynamic memory allocation refers to performing dynamic memory allocation in the C via a group of functions in the C standard library, namely malloc, realloc, calloc and free....
and free) - shared library linking.
Much of the library, and perhaps the overall thrust of it in the Gromit environment, provides the underpinnings of the Java virtual machine, more or less mapping the sys layer that Sun
Sun Microsystems
Sun Microsystems, Inc. was a company that sold :computers, computer components, :computer software, and :information technology services. Sun was founded on February 24, 1982...
defines for the porting
Porting
In computer science, porting is the process of adapting software so that an executable program can be created for a computing environment that is different from the one for which it was originally designed...
of the Java VM to various platforms. NSPR does go beyond that requirement in some areas, as it also functions as the platform-independent layer for most of the servers produced by Netscape
Netscape
Netscape Communications is a US computer services company, best known for Netscape Navigator, its web browser. When it was an independent company, its headquarters were in Mountain View, California...
.
Some manufacturers expect and prefer that programmers restructure and perhaps even rewrite existing code in order to use the NSPR API
Application programming interface
An application programming interface is a source code based specification intended to be used as an interface by software components to communicate with each other...
. NSPR does not have as a goal the provision of a platform for the porting into Netscape of externally developed code.
History
The first generation of NSPR originally aimed just to satisfy the requirements of porting JavaJava (programming language)
Java is a programming language originally developed by James Gosling at Sun Microsystems and released in 1995 as a core component of Sun Microsystems' Java platform. The language derives much of its syntax from C and C++ but has a simpler object model and fewer low-level facilities...
to various host environments. NSPR20, an effort started in 1996, built on that original idea, though very little remains of the original code. (The "20" in "NSPR20" does not mean "version 2.0" but rather "second generation".) Many of the concepts show reform, expansion, and maturation. NSPR may still function appropriately as the platform-dependent layer under Java, but it primarily serves in supporting client
Client (computing)
A client is an application or system that accesses a service made available by a server. The server is often on another computer system, in which case the client accesses the service by way of a network....
s written entirely in C
C (programming language)
C is a general-purpose computer programming language developed between 1969 and 1973 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system....
or in C++
C++
C++ is a statically typed, free-form, multi-paradigm, compiled, general-purpose programming language. It is regarded as an intermediate-level language, as it comprises a combination of both high-level and low-level language features. It was developed by Bjarne Stroustrup starting in 1979 at Bell...
.
How it works
NSPR has the goal of providing uniform service over a wide range of operating-system environments. It strives to not export the lowest common denominator, but to exploit the best features of each operating system on which it runs, while still providing a uniform service across a wide range of host offerings.Threads
ThreadThread (computer science)
In computer science, a thread of execution is the smallest unit of processing that can be scheduled by an operating system. The implementation of threads and processes differs from one operating system to another, but in most cases, a thread is contained inside a process...
s feature prominently in NSPR. The software industry
Software industry
The software industry includes businesses involved in the development, maintenance and publication of computer software using any business model...
's offering of threads lacks consistency. NSPR, while far from perfect, does provide a single API to which clients may program and expect reasonably consistent behavior. The operating systems provide everything from no concept of threading at all up to and including sophisticated, scalable and efficient implementations. NSPR makes as much use of what the systems offer as it can. NSPR aims to impose as little overhead
Computational overhead
In computer science, overhead is generally considered any combination of excess or indirect computation time, memory, bandwidth, or other resources that are required to attain a particular goal...
as possible in accessing those appropriate system features.
Thread synchronization
Thread synchronization loosely depends on monitorMonitor (synchronization)
In concurrent programming, a monitor is an object or module intended to be used safely by more than one thread. The defining characteristic of a monitor is that its methods are executed with mutual exclusion. That is, at each point in time, at most one thread may be executing any of its methods...
s as described by C. A. R. Hoare
C. A. R. Hoare
Sir Charles Antony Richard Hoare , commonly known as Tony Hoare or C. A. R. Hoare, is a British computer scientist best known for the development of Quicksort, one of the world's most widely used sorting algorithms...
in "Monitors: An operating system structuring concept", Communications of the ACM
Communications of the ACM
Communications of the ACM is the flagship monthly journal of the Association for Computing Machinery . First published in 1957, CACM is sent to all ACM members, currently numbering about 80,000. The articles are intended for readers with backgrounds in all areas of computer science and information...
, 17(10), October 1974 and then formalized by Xerox
Xerox
Xerox Corporation is an American multinational document management corporation that produced and sells a range of color and black-and-white printers, multifunction systems, photo copiers, digital production printing presses, and related consulting services and supplies...
' Mesa programming language
Mesa programming language
Mesa was an innovative programming language developed in the late 1970s at the Xerox Palo Alto Research Center in Palo Alto, California, United States. The language was named after the mesas of the American Southwest, referring to its design intent to be a "high-level" programming language.Mesa is...
("Mesa Language Manual", J.G. Mitchell et al., Xerox PARC, CSL-79-3 (Apr 1979)). This mechanism provides the basic mutual exclusion (mutex) and thread notification facilities (condition variables) implemented by NSPR. Additionally, NSPR provides synchronization methods more suited for use by Java. The Java-like facilities include monitor reentrancy, implicit and tightly bound notification capabilities with the ability to associate the synchronization objects dynamically.
I/O
NSPR's I/OI/O
I/O may refer to:* Input/output, a system of communication for information processing systems* Input-output model, an economic model of flow prediction between sectors...
slightly augments the Berkeley sockets
Berkeley sockets
The Berkeley sockets application programming interface comprises a library for developing applications in the C programming language that perform inter-process communication, most commonly for communications across a computer network....
model and allows arbitrary layering. The designers originally intended to export synchronous I/O methods only, relying on threads to provide the concurrency needed for complex applications. That method of operation remains preferred, though one can configure the network I/O channels as non-blocking in the traditional sense.
Network addresses
Part of NSPR deals with manipulation of network addresses. NSPR defines an IPInternet Protocol
The Internet Protocol is the principal communications protocol used for relaying datagrams across an internetwork using the Internet Protocol Suite...
-centric network address object. While it does not define the object as opaque, the API provides methods that allow and encourage clients to treat the addresses as polymorphic
Type polymorphism
In computer science, polymorphism is a programming language feature that allows values of different data types to be handled using a uniform interface. The concept of parametric polymorphism applies to both data types and functions...
items. In this area NSPR aims to provide a migration path between IPv4
IPv4
Internet Protocol version 4 is the fourth revision in the development of the Internet Protocol and the first version of the protocol to be widely deployed. Together with IPv6, it is at the core of standards-based internetworking methods of the Internet...
and IPv6
IPv6
Internet Protocol version 6 is a version of the Internet Protocol . It is designed to succeed the Internet Protocol version 4...
. To that end one can perform translations of ASCII
ASCII
The American Standard Code for Information Interchange is a character-encoding scheme based on the ordering of the English alphabet. ASCII codes represent text in computers, communications equipment, and other devices that use text...
strings (DNS
Domain name system
The Domain Name System is a hierarchical distributed naming system for computers, services, or any resource connected to the Internet or a private network. It associates various information with domain names assigned to each of the participating entities...
names) into NSPR's network address structures, regardless of whether the addressing technology uses IPv4 or IPv6.
Time
NSPR makes timing facilities available in two forms: interval timing and calendar functions.Interval timers are based on a free running, 32-bit, platform-dependent resolution timer. Such timers are normally used to specify timeouts on I/O, waiting on condition variables and other rudimentary thread scheduling. Since these timers have finite namespace and are free running, they can wrap at any time. NSPR does not provide an epoch, but expects clients to deal with that issue. The granularity of the timers is guaranteed to be between 10 microseconds and 1 millisecond. This allows a minimal timer period in of approximately 12 hours. But in order to deal with the wrap-around issue, only half that namespace may be utilized. Therefore, the minimal usable interval available from the timers is slightly less than six hours.
Calendar times are 64-bit signed numbers with units of microseconds. The epoch for calendar times is midnight, January 1, 1970, Greenwich Mean Time
Greenwich Mean Time
Greenwich Mean Time is a term originally referring to mean solar time at the Royal Observatory in Greenwich, London. It is arguably the same as Coordinated Universal Time and when this is viewed as a time zone the name Greenwich Mean Time is especially used by bodies connected with the United...
. Negative times extend to times before 1970, and positive numbers forward. Use of 64 bits allows a representation of times approximately in the range of −30000 to the year 30000. There exits a structural representation (i.e., exploded view), routines to acquire the current time from the host system, and convert them to and from the 64-bit and structural representation. Additionally there are routines to convert to and from most well-known forms of ASCII into the 64-bit NSPR representation.
Memory management
NSPR provides API to perform the basic mallocMalloc
C dynamic memory allocation refers to performing dynamic memory allocation in the C via a group of functions in the C standard library, namely malloc, realloc, calloc and free....
, calloc, realloc and free functions. Depending on the platform, the functions may be implemented almost entirely in the NSPR runtime or simply shims that call immediately into the host operating system's offerings.
Linking
Support for linking (shared library loading and unloading) forms part of NSPR's feature set. In most cases this is simply a smoothing over of the facilities offered by the various platform providers.See also
- Apache Portable RuntimeApache Portable RuntimeThe Apache Portable Runtime is a supporting library for the Apache web server. It provides a set of APIs that map to the underlying operating system . Where the OS doesn't support a particular function, APR will provide an emulation...
- Adaptive Communication EnvironmentAdaptive Communication EnvironmentThe Adaptive Communication Environment is an open-source framework used to simplify various aspects of network programming...
- Cross-Platform Support MiddlewareCross-Platform Support MiddlewareA cross-platform support middleware is a software abstraction layer that guarantees the existence, and correct implementation, of a set of services on top a set of platforms.-Formal model:Formally, a CPSM can be represented by the following model:...