D. C. Schmidt, "The Object-Oriented Design and Implementation of the Reactor: A C++ Wrapper for UNIX I/O Multiplexing (Part 2 of 2 )," C++ Report, Vol. 5, September 1993.  Home/Search   Document Not in Database   Summary   Related Articles   Check

....details of design and implementation of RTSS. We present results of performance measurements in Section 5 and conclude the paper in Section 6. 2 2. RELATED WORK Several advances have been made in improving existing distributed object computing environment. They include: the C wrappers by [6][7] which does not provide QOS guarantees for real time streams; the Realvideo [8] and Vxtreme [9] which are not CORBA based and rely on proprietary stream establishment and control mechanisms to access multimedia context; the multimedia information stream services (MISS) 10] which is not CORBA ....

D. C. Schmidt, "The Object-Oriented Design and Implementation of the Reactor: A C++ Wrapper for UNIX I/O Multiplexing (Part 2 of 2 )," C++ Report, Vol. 5, September 1993.

....uses of the IPC SAP class categories. For example, the following paper describes a related communication software development tool called the Reactor. The Reactor encapsulates the functionality of the select and poll event demultiplexing mechanisms within a portable and extensible C wrapper [25, 26]. Select and poll are UNIX system calls that detect the occurrence of different types of input and output events on one or more I O descriptors simultaneously. Together, IPC SAP and the Reactor provide an efficient and extensible suite of reusable software components that simplify the development ....

D. C. Schmidt, "The Object-Oriented Design and Implementation of the Reactor: A C++ Wrapper for UNIX I/O Multiplexing (Part 2 of 2)," C++ Report, vol. 5, September 1993.

....components. Inheritance, dynamic binding, and object composition are C language features that help enforce dependencies and decouple implementations within a framework. This paper presents a case study that describes the evolution of an object oriented framework called the Reactor [8, 9]. The Reactor framework supports concurrent event demultiplexing and event handler dispatching. Event handlers are triggered by various types of events (such as timers, synchronization objects, signals, or I O events) The pri SERVER CLIENT NETWORK 2: FORWARDED REQUEST 3: RESPONSE ....

....the underlying event demultiplexer. Although portions of the Reactor s internal implementation changed, its external interface remained the same for both the select based and the poll based versions. This common interface facilitates networking application portability between System V and BSD UNIX [9]. A portion of the public interface for the UNIX implementation of the Reactor pattern is shown below: Bit wise or these values to check for multiple activities per descriptor enum Reactor Mask READ MASK = 01, WRITE MASK = 02, EXCEPT MASK = 04, RWE MASK = READ MASK WRITE MASK ....

[Article contains additional citation context not shown here]

D. C. Schmidt, "The Object-Oriented Design and Implementation of the Reactor: A C++ Wrapper for UNIX I/O Multiplexing (Part 2 of 2)," C++ Report, vol. 5, September 1993.

.... (such as message managers, timer based event managers, demultiplexers [10] and assorted protocol functions and mechanisms [11] class hierarchies (such as an inheritance lattice of mechanisms for local and remote interprocess communication [1] class categories (such as event demultiplexers [12, 13]) and objects (such as a service dispatch table) By emphasizing the integration and collaboration of application specific and application independent components, frameworks enable larger scale reuse of software compared with simply reusing individual classes or stand alone functions. The ASX ....

....user level execution agents. 2. 2 The Object Oriented Architecture of ASX The architecture of the ASX framework was developed incrementally by generalizing from extensive design and implementation experience with a range of distributed applications including on line transaction processing systems [13], realtime PBX performance monitoring systems [3] and multiprocessor based communication subsystems. After building several prototypes and iterating through a number of alternative designs, the class categories illustrated in Figure 1 were identified and implemented. A class category is a ....

[Article contains additional citation context not shown here]

D. C. Schmidt, "The Object-Oriented Design and Implementation of the Reactor: A C++ Wrapper for UNIX I/O Multiplexing (Part 2 of 2)," C++ Report, vol. 5, September 1993.

....for their application QoS requirements: Wait on Read: In this strategy, the calling thread blocks on read to receive the reply. This is a very efficient strategy for pure clients that need not receive requests or nested upcalls while waiting for server replies. Wait on Reactor: The Reactor [27] is a framework implemented in ACE [24] that provides event demultiplexing and event handler dispatching. In this strategy, a single threaded Reactor is used to dispatch events, such as reply arrivals and upcalls. This strategy supports single threaded client applications efficiently by having the ....

D. C. Schmidt, "The Object-Oriented Design and Implementation of the Reactor: A C++ Wrapper for UNIX I/O Multiplexing (Part 2 of 2)," C++ Report, vol. 5, September 1993.

....and WaitForMultipleObjects [7] with an extensible and portable callback driven object oriented interface. The Reactor pattern enables efficient demultiplexing of multiple types of events from multiple sources within a single thread of control. An implementation of the Reactor pattern is shown in [8] and the two omain roles in the Reactive layer are describe below. # Reactor: This class defines an interface for registering, removing, and dispatching Event Handler objects (such as the Connector and Svc Handler) An implementation of the Reactor interface provides a set of ....

D. C. Schmidt, "The Object-Oriented Design and Implementation of the Reactor: A C++ Wrapper for UNIX I/O Multiplexing (Part 2 of 2)," C++ Report, vol. 5, September 1993.

....and WaitForMultipleObjects [11] with an extensible and portable callback driven object oriented interface. The Reactor pattern enables efficient demultiplexing of multipletypes of events from multiple sources withina single thread of control. An implementation of the Reactor pattern is shown in [12] and the two main roles in the Reactive layer are describe below. # Reactor: This class defines an interface for registering, removing, and dispatching Event Handler objects (such as the Acceptor and Svc Handler) An implementation of the Reactor interface provides a set of ....

D. C. Schmidt, "The Object-Oriented Design and Implementation of the Reactor: A C++ Wrapper for UNIX I/O Multiplexing (Part 2 of 2)," C++ Report, vol. 5, September 1993.

....their application QoS requirements: ffl Wait on Read: In this strategy, the calling thread blocks on read to receive the reply. This is a very efficient strategy for the pure clients that do not receive requests or nested upcalls while waiting for server replies. ffl Wait on Reactor: The Reactor [27] is a framework implemented in ACE [24] that provides event demultiplexing and event handler dispatching. In this strategy, a single threaded Reactor is used to dispatch events, such as reply arrivals and upcalls. This strategy supports single threaded client applications efficiently. In this ....

D. C. Schmidt, "The Object-Oriented Design and Implementation of the Reactor: A C++ Wrapper for UNIX I/O Multiplexing (Part 2 of 2)," C++ Report, vol. 5, September 1993.

....mechanism that s most appropriate for their applications: 1. Wait on Read In this strategy, the calling thread blocks on read to receive the reply. This is a very efficient strategy for the pure clients that do not have to receive upcalls while waiting for replies. 2. Wait on Reactor: Reactor [14] is a framework implemented in ACE [12] to provide event demultiplexing and event handler dispatching. In this strategy, singlethreaded Reactor is used to dispatch the events such as reply arrivals and upcalls. This strategy efficiently supports single threaded client applications. In this ....

D. C. Schmidt, "The Object-Oriented Design and Implementation of the Reactor: A C++ Wrapper for UNIX I/O Multiplexing (Part 2 of 2)," C++ Report, vol. 5, September 1993.

....(ACE) 6] ACE is a freely available OO toolkit containing a rich set of reusable wrappers, class categories, and frameworks that perform common network programming tasks across a wide range of OS platforms. The tasks provided by ACE include: ffl Event demultiplexing and event handler dispatching[13, 14, 10, 15]; ffl Connection establishment and service initialization [16, 17, 18] ffl Interprocess communication [19, 4] and shared memory management; ffl Dynamic configuration of distributed communication services [20, 21] ffl Concurrency parallelism and synchronization [22, 23, 11, 24] ffl ....

....TCP CONNECTION Figure 13: The Distributed Logging Facility dows and or on different remote host systems. Therefore, ACE provides a distributed logging facility that simplifies debugging and run time tracing. This facility is currently used in a commercial on line transaction processing system [14] to provide logging services for a cluster of workstations and multi processor database servers in a high speed network environment. As shown in Figure 13, the distributed logging facility allows applications running on multiple client hosts to send logging records to a server logging daemon ....

[Article contains additional citation context not shown here]

D. C. Schmidt, "The Object-Oriented Design and Implementation of the Reactor: A C++ Wrapper for UNIX I/O Multiplexing (Part 2 of 2)," C++ Report, vol. 5, September 1993.

....in generalizing from existing code by using templates and overloading to transparently parameterize synchronization mechanisms into a concurrent application. Some of the infrastructure code is based on components in the freely available ADAPTIVE Service eXecutive (ASX) framework described in [1, 2, 3, 4, 5]. 2 Motivation The following C code illustrates part of the main eventloop of a typical distributed application (such as an object location broker [6] or a multi threaded network file server) Example 1 typedef unsigned long COUNTER; COUNTER request count; At file scope void run svc ....

....thread that owns the Mutex is the one that re acquires it. For example, if an Atomic Op counter is called by multiple nested function calls within the same thread, a recursive mutex will prevent deadlock from occurring. Recursive mutexes are particularly useful for callbackdriven C frameworks [11, 3, 4], where the framework event loop performs a callback to arbitrary user defined code. Since the user defined code may subsequently re enter framework code via a method entry point, recursive mutexes may be necessary to prevent deadlock from occurring on locks held within the framework during the ....

D. C. Schmidt, "The Object-Oriented Design and Implementation of the Reactor: A C++ Wrapper for UNIX I/O Multiplexing (Part 2 of 2)," C++ Report, vol. 5, September 1993.

.... to provide a set of related interfaces and services [4] The primary class categories supported by ACE include: ffl Reactor performs event demultiplexing and event handler dispatching by encapsulating OS event demultiplexing mechanisms (such as select, poll, and WaitForMultipleObjects) [17, 18]. ffl IPC SAP which encapsulates local and or remote IPC mechanisms such as sockets, TLI, and memory mapped files [19, 3] ffl Connection encapsulates active passive connection establishment mechanisms [20] ffl Concurrency encapsulates and extends multithreading and synchronization ....

....challenging since diagnostic output appears in different windows and or on different remote host systems. Therefore, ACE provides a distributed logging facility that simplifies debugging and run time tracing. This facility is currently used in a commercial on line transaction processing system [18] to provide logging services for a cluster of workstations and multi processordatabase servers in a high speed network environment. As shown in Figure 12, the distributed logging facility allows applications running on multiple client hosts to send logging records to a server logging daemon ....

[Article contains additional citation context not shown here]

D. C. Schmidt, "The Object-Oriented Design and Implementation of the Reactor: A C++ Wrapper for UNIX I/O Multiplexing (Part 2 of 2)," C++ Report, vol. 5, September 1993.

....and WaitForMultipleObjects [11] with an extensible and portable callback driven object oriented interface. The Reactor pattern enables efficient demultiplexing of multipletypes of events from multiple sources withina single thread of control. An implementation of the Reactor pattern is shown in [12] and the two main roles in the Reactive layer are describe below. ffl Reactor: This class defines an interface for registering, removing, and dispatching Event Handler objects (such as the Acceptor and Svc Handler) An implementation of the Reactor interface provides a set of ....

D. C. Schmidt, "The Object-Oriented Design and Implementation of the Reactor: A C++ Wrapper for UNIX I/O Multiplexing (Part 2 of 2)," C++ Report, vol. 5, September 1993.

....TLI, STREAM pipe, and named pipe mechanisms via an object oriented interface. ffl The I O based and timer based event demultiplexing mechanisms used to dispatch incoming connection requests and data onto the appropriate applicationspecified service. A sub framework within ASX called the Reactor [16] portably encapsulates both the select and poll I O demultiplexing system calls via an object oriented interface. ffl Execution Agents: ffl The type and number of execution agents and process architectures used to perform services at run time. Developers may select between user level and ....

....and or on remote host systems. As shown in Figure 4, the ACE distributed logging facility consists of several interoperating components located on multiple machines throughout an internetwork (the complete design and implementation of the distributed logging facility is described in detail in [25, 16]) Application processes (e.g. P 1 , P 2 , P 3 ) running on client hosts use the Log Msg C class to generate various types of logging records (such as LOG ERROR and LOG DEBUG) The Log Msg: log method provides a printf style interface that timestamps logging records and sends them via the FIFO ....

[Article contains additional citation context not shown here]

D. C. Schmidt, "The Object-Oriented Design and Implementation of the Reactor: A C++ Wrapper for UNIX I/O Multiplexing (Part 2 of 2)," C++ Report, vol. 5, September 1993.

.... receives the messages and displays them on one or more output devices (such as a printer, persistent storage device, or monitoring console) Subsequent articles will address this client server architecture in greater detail using the Reactor I O based and timer based service multiplexing facility [2, 3]. 2.1 Limitations with Existing Operating System Interfaces Developing communication system software is difficult since it requires detailed knowledge of many concepts such as (1) network addressing and remote service identification, 2) creation, synchronization, and communication mechanisms for ....

....OS APIs is that it is difficult to specialize or generalize their functionality without writing new code and or modifying existing application code. On the other hand, APIs that use objectoriented features such as inheritance and dynamic binding are typically easy to extended transparently [3]. Extensibility becomes particularly important when dealing with C wrapper that provide more complex semantics (such as event multiplexing and multi processing) 2.2 The C Wrapper Alternative Switching to a consistently designed, strongly typed, objectoriented operating system (such as the ....

[Article contains additional citation context not shown here]

D. C. Schmidt, "The Object-Oriented Design and Implementation of the Reactor: AC++Wrapper for UNIX I/O Multiplexing (Part 2 of 2)," C++ Report, vol. 5, September 1993.

....in generalizing from existing code by using templates and overloading to transparently parameterize synchronization mechanisms into a concurrent application. Some of the infrastructure code is based on components in the freely available ADAPTIVE Service eXecutive (ASX) framework described in [1, 2, 3, 4, 5]. 2 Motivation The following C code illustrates part of the main eventloop of a typical distributed application (such as an object location broker [6] or a multi threaded network file server) Example 1 typedef unsigned long COUNTER; COUNTER request count; At file scope void run svc ....

....thread that owns the Mutex is the one that re acquires it. For example, if an Atomic Op counter is called by multiple nested function calls within the same thread, a recursive mutex will prevent deadlock from occurring. Recursive mutexes are particularly useful for callbackdriven C frameworks [11, 3, 4], where the framework event loop performs a callback to arbitrary user defined code. Since the user defined code may subsequently re enter framework code via a method entry point, recursive mutexes may be necessary to prevent deadlock from occurring on locks held within the framework during the ....

D. C. Schmidt, "The Object-Oriented Design and Implementation of the Reactor: A C++ Wrapper for UNIX I/O Multiplexing (Part 2 of 2)," C++ Report, vol. 5, September 1993.

.... the server caches the client s host name (illustrated by the ovals in the logging server daemon) and uses this information to identify the client in the formatted records it prints to the output device(s) The complete design and implementation of the distributed logging facility is described in [3]. The remainder of the current article presents the necessary background material by exploringseveral alternative UNIX mechanisms for handling I O from multiple sources. 3 Operating System Event Demultiplexing Modern operating systems such as UNIX, Windows NT, and OS 2 offer several techniques ....

D. C. Schmidt, "The Object-Oriented Design and Implementation of the Reactor: A C++ Wrapper for UNIX I/O Multiplexing (Part 2 of 2)," C++ Report, vol. 5, September 1993.

....uses of the IPC SAP class categories. For example, the following paper describes a related communication software development tool called the Reactor. The Reactor encapsulates the functionality of the select and poll event demultiplexing mechanisms within a portable and extensible C wrapper [23, 24]. Select and poll are UNIX system calls that detect the occurrence of different types of input and output events on one or more I O descriptors simultaneously. Together, IPC SAP and the Reactor provide an efficient and extensible suite of reusable software components that simplify the development ....

D. C. Schmidt, "The Object-Oriented Design and Implementation of the Reactor: A C++ Wrapper for UNIX I/O Multiplexing (Part 2 of 2)," C++ Report, vol. 5, September 1993.

.... the server caches the client s host name (illustrated by the ovals in the logging server daemon) and uses this information to identify the client in the formatted records it prints to the output device(s) The complete design and implementation of the distributed logging facility is described in [3]. The remainder of the current article presents the necessary background material by exploring several alternative mechanisms for handling I O from multiple sources. 3 Operating System Event Demultiplexing Modern operating systems such as UNIX, Windows NT, and OS 2 offer several techniques that ....

....Event Handler base class. An instance of this class is then constructed and registered with the Reactor. After registration, the server initiates an event loop that automatically dispatches the Logging Acceptor: handle input member function when connection requests arrive. A subsequent article [3] describes the design and implementation of the Logging Acceptor and Logging Handler classes and other components used to implement the Reactor in greater detail. Non Portable Interfaces: Although event demultiplexing is not part of the POSIX standard, System V Release 4, BSD UNIX, and WINSOCK ....

D. C. Schmidt, "The Object-Oriented Design and Implementation of the Reactor: A C++ Wrapper for UNIX I/O Multiplexing (Part 2 of 2)," C++ Report, vol. 5, September 1993.

....the development of reliable, robust, and extensible distributed applications. Previous articles in this series have examined C wrappers that encapsulate the socket interprocess communication (IPC) interface [1] and the event demultiplexing mechanisms provided by the select and poll system calls [2, 3]. This article presents an object oriented domain analysis of key design dimensions for network server daemons. Subsequent articles will describe a framework called the ADAPTIVE Service eXecutive (ASX) 4] that provides flexibility across the design dimensions identified in this article. The ASX ....

....dimensions, 4) concurrency dimensions, and (5) configuration dimensions listed in Figure 2. These five dimensions were identified by generalizing from practical design and implementation experience with a number of distributed applications ranging from on line transaction processing systems [3], PBX switch performance monitoring systems [9] and multi processor based communication subsystems [4] Each of the five dimensions discussed below offer a set of relatively orthogonal design alternatives. These alternatives are examined to define the vocabulary of the network daemon domain, ....

D. C. Schmidt, "The Object-Oriented Design and Implementation of the Reactor: A C++ Wrapper for UNIX I/O Multiplexing (Part 2 of 2)," C++ Report, vol. 5, September 1993.

....and WaitForMultipleObjects [7] with an extensible and portable callback driven object oriented interface. The Reactor pattern enables efficient demultiplexing of multiple types of events from multiple sources within a single thread of control. An implementation of the Reactor pattern is shown in [8] and the two omain roles in the Reactive layer are describe below. ffl Reactor: This class defines an interface for registering, removing, and dispatching Event Handler objects (such as the Connector and Svc Handler) An implementation of the Reactor interface provides a set of ....

D. C. Schmidt, "The Object-Oriented Design and Implementation of the Reactor: A C++ Wrapper for UNIX I/O Multiplexing (Part 2 of 2)," C++ Report, vol. 5, September 1993.

....e.g. initial server startup time or even during run time. As described below, the SVC CONframework provides several foundation classes that support the deferred binding of services onto processes and or threads. Other object oriented components used by the EOS applications are described elsewhere [3, 4, 5]. 3 The Service Configurator Framework The SVC CON provides an object oriented framework that simplifies the development, configuration, and reconfiguration of concurrent, multi service network daemons. A daemon is a statically or dynamically configured process that executes in the background ....

....logging, daemonization, service directory functionality, and various process, thread, and linking strategies) into reusable C foundation classes. These classes include the IPC SAP object oriented transport interface [3] and the Reactor I O based and timer based event multiplexing class library [4, 5] (both of which enhance application robustness by accessing OS local and remote IPC mechanisms via type secure interfaces, rather than the weakly typed descriptor based underlying system call interfaces) 3.1 Conventional Port Monitoring and Service Dispatching Frameworks This section describes ....

[Article contains additional citation context not shown here]

D. C. Schmidt, "The Object-Oriented Design and Implementation of the Reactor: A C++ Wrapper for UNIX I/O Multiplexing (Part 2 of 2)," C++ Report, vol. 5, September 1993.

....services. 4 The C Wrappers Solution Using C wrappers is one way to simplify the complexity of programming network servers. C wrappers encapsulate lower level network programming interfaces such as sockets and select with type safe, object oriented interfaces. The IPC SAP [5] Reactor [4, 6], and Acceptor [7] C wrappers shown below are part of the ACE object oriented network programming toolkit. IPC SAP encapsulates sockets and TLI network programming interfaces; the Reactor encapsulates the select and poll event demultiplexing system calls; and the Acceptor combines IPC SAP and ....

D. C. Schmidt, "The Object-Oriented Design and Implementation of the Reactor: A C++ Wrapper for UNIX I/O Multiplexing (Part 2 of 2)," C++ Report, vol. 5, September 1993.

.... to provide a set of related interfaces and services [4] The primary class categories supported by ACE include: ffl Reactor performs event demultiplexing and event handler dispatching by encapsulating OS event demultiplexing mechanisms (such as select, poll, and WaitForMultipleObjects) [16, 17]. ffl IPC SAP which encapsulates local and or remote IPC mechanisms such as sockets, TLI, and memory mapped files [18, 3] ffl Connection encapsulates active passive connection establishment mechanisms [19] Reactor REGISTERED OBJECTS FRAMEWORK LEVEL KERNEL LEVEL APPLICATION LEVEL OS ....

....challenging since diagnostic output appears in different windows and or on different remote host systems. Therefore, ACE provides a distributed logging facility that simplifies debugging and run time tracing. This facility is currently used in a commercial on line transaction processing system [17] to provide logging services for a cluster of workstations and multi processor database servers in a high speed network environment. As shown in Figure 12, the distributed logging facility allows applications running on multiple client hosts to send logging records to a server logging daemon ....

[Article contains additional citation context not shown here]

D. C. Schmidt, "The Object-Oriented Design and Implementation of the Reactor: A C++ Wrapper for UNIX I/O Multiplexing (Part 2 of 2)," C++ Report, vol. 5, September 1993.

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