WO2001086417A2 - A finite state machine in a portable thread environment - Google Patents
A finite state machine in a portable thread environment Download PDFInfo
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- WO2001086417A2 WO2001086417A2 PCT/US2001/014933 US0114933W WO0186417A2 WO 2001086417 A2 WO2001086417 A2 WO 2001086417A2 US 0114933 W US0114933 W US 0114933W WO 0186417 A2 WO0186417 A2 WO 0186417A2
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- state machine
- state
- thread
- pte
- threads
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F9/00—Arrangements for program control, e.g. control units
- G06F9/06—Arrangements for program control, e.g. control units using stored programs, i.e. using an internal store of processing equipment to receive or retain programs
- G06F9/46—Multiprogramming arrangements
- G06F9/54—Interprogram communication
- G06F9/542—Event management; Broadcasting; Multicasting; Notifications
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- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F9/00—Arrangements for program control, e.g. control units
- G06F9/06—Arrangements for program control, e.g. control units using stored programs, i.e. using an internal store of processing equipment to receive or retain programs
- G06F9/46—Multiprogramming arrangements
- G06F9/54—Interprogram communication
- G06F9/546—Message passing systems or structures, e.g. queues
Definitions
- This invention relates generally to the field for software design; and, more particularly, to a finite state machine in an application environment supporting portable, embedded, concurrent, and/or real-time applications.
- the term "application” is commonly used to refer to the objective or problem for which the software, or "application program,” is a solution.
- the form of the solution - the application program - is dependent, in part, on the configuration of the hardware on which the software is executed and, in part, on the other programs that may be executing in concert with the application program.
- An application program is typically translated from an instruction set derived from one of several well-known programming languages to an instruction set closely reflecting the capabilities of processor executing the application program. This translation is accomplished by programs generally know as “compilers,” “assemblers” or “interpreters.” These programs translate the application program's original instructions to a set of instruction typically know as “machine code” for which there is a one-to-one correspondence between machine code instructions and the unitary operations the machine (or processor) is able to perform. Typically, machine code instructions are dependent on the machine's central processing unit (or CPU). The operation of these and similar programs are well known to those of ordinary skill in the art.
- Application programs are frequently executed simultaneously with other application programs, sharing (and sometimes competing for) the resources of the host hardware.
- ISR interrupts service routines
- Application programs may be invoked by, or may invoke, the services of other sets of programs running on the host that are collectively know as an "operating system.”
- Operating system programs are typically responsible for controlling the allocation of the host's resources, including access to the host machine's data stores, central processing unit, and input/output devices.
- One aspect of controlling the allocation of a host's resources typically involves insuring that no two applications, ISRs, or portions of the same application try to control a resource at the same time.
- a number of techniques for preventing this are well know in the art, including semaphores, counting semaphores, mutexes, signals, and critical sections.
- a critical section is a portion of a program that, once started, is uninterruptible and executes continuously without allowing other programs to run until the critical section has ended.
- Application software is executed within some "host environment,” defined collectively by the host machine's hardware (including, possibly, application-specific support hardware such as an application-specific integrated circuit or "ASIC") and operating system.
- host environment defined collectively by the host machine's hardware (including, possibly, application-specific support hardware such as an application-specific integrated circuit or "ASIC") and operating system.
- ASIC application-specific integrated circuit
- a problem with the traditional porting method is that this method requires that at least some portion of the application program be rewritten. This is a potentially costly and error-prone process. Because there is a likelihood of introducing unintentional errors whenever the application program is altered, this method mandates that the application developer bare the additional expense of re-testing the application after the indicated changes are complete.
- a finite state machine in a portable thread environment comprises a finite state machine operating within a portable thread environment; and one or more PTE message generators configured to pass state information contained in PTE messages to the finite state machine, wherein the finite state machine changes states according to the state information.
- FIG. 1 illustrates an application having two tasks, one task comprised of four threads and the other task comprised of three threads.
- FIG. 2 illustrates message flow between a scheduling queue, a scheduler, and various threads according to one embodiment of the invention.
- FIG. 3 illustrates one embodiment of a portable thread environment (a PTE application interface and a host environment interface layer) and its relationship to an application program and a host environment including an operating system.
- FIG. 4 illustrates an embodiment of a portable thread environment implemented without an embedded operating system.
- FIG. 5 illustrates two tasks communicating through a portable thread application programming interface.
- FIG. 6 illustrates two tasks residing in separate portable thread environments and communicating through an application programming interface.
- FIG. 7 illustrates a preemptive task and a cooperative task communicating with an external source and /or destination through an application programming interface.
- FIGS. 8a-d illustrates various examples of coordination between preemptive tasks and cooperative tasks.
- FIG. 9 illustrates various thread states according to one embodiment of the invention.
- FIG.10 illustrates a scheduling function according to one embodiment communicating with various system queues.
- FIG. 11 illustrates scheduler operation according to one embodiment of the invention.
- FIG. 12 illustrates message routing logic according to one embodiment of the invention.
- FIGS.13a illustrates a thread attribute table according to one embodiment of the invention.
- FIGS.13b illustrates a task status table according to one embodiment of the invention.
- FIGS. 13c illustrates a preempted task table according to one embodiment of the invention.
- FIG.14 illustrates a wireless protocol stack implemented using one embodiment of the invention.
- FIG.15 illustrates a finite state machine (FSM) 1500 built into the messaging structure of the PTE.
- FSM finite state machine
- Embodiments of the invention described below seek to avoid the problems associated with porting application software by creating a portable environment in which an application can be moved from one host environment to another unchanged.
- an application 100 is constructed as a series of short, sequentially executed program fragments, referred to herein as "threads" 111-117.
- Each thread 111-117 is assigned to a logical grouping called a "task" 110, 120.
- threads 111- 114 are grouped within task 110 and threads 115-117 are grouped within task 120.
- tasks may be used to partition an application into one or more sub-units, each accomplishing a specific function.
- An application may be subdivided into any number of tasks and each task may contain any number of threads.
- PTE Portable Thread Environment
- one embodiment of the invention includes a Portable Thread Environment ("PTE") which is comprised generally of a scheduler 220, one or more scheduling queues 215, and a host adaptation layer 210.
- PTE Portable Thread Environment
- the scheduling queue 215 accepts messages from executing threads (e.g., internal message source 206) and/or from sources external to the PTE (e.g., external message source 205). Each PTE-supported message is tagged with a code (e.g., a value or name) uniquely identifying a thread to which that message is to be delivered.
- executing threads e.g., internal message source 206
- sources external to the PTE e.g., external message source 205.
- Each PTE-supported message is tagged with a code (e.g., a value or name) uniquely identifying a thread to which that message is to be delivered.
- threads are executed by the PTE scheduler
- the scheduling queue 215 in one embodiment is a list formed as messages are received from internal sources 206 such as running threads and from external sources 205 with which the application interacts.
- internal sources 206 such as running threads and from external sources 205 with which the application interacts.
- external message source is application-specific support hardware found the host environment.
- Threads which are members of the same task may share information through common memory stores or by passing messages between themselves. By contrast, in one embodiment, threads which are members of different tasks may exchanges data only by sending messages.
- the task grouping is designed (in part) to support the use of application-specific support hardware in an application's design. When an application is designed, the functions which are to be supported by application- specific hardware are modeled in the form of one or more tasks. When the application-specific circuits are subsequently incorporated into the design, the tasks are removed from the application software 230 (i.e., they are provided by the application-specific circuit).
- the host adaptation layer 210 in one embodiment ensures that messaging between threads in different tasks is identical to the messaging between threads and an application's support hardware.
- the application programming interface (“API") used by the application is consistent, regardless of whether application-specific circuits are involved.
- API application programming interface
- the inclusion of an application-specific circuit therefore, does not require modifications to the underlying application code (in one embodiment only an small amount of code in the host adaptation layer 210 is modified). As such, in this embodiment the application is effectively shielded from the host environment.
- the PTE and application can run in a stand-alone configuration as depicted in Figure 4.
- the host adaptation layer 420 supplies any necessary hardware support (i.e., interfaces) and communicates to the internal application threads through the PTE messaging system.
- Figure 5 illustrates message transport between tasks/threads according to one embodiment of the invention in greater detail.
- Task 520 in this embodiment communicates with task 530 by a message exchange between thread 522 and 532, respectively.
- the inter-thread message passing is accomplished via the portable thread environment API 540.
- threads within the same task 530 may also communicate (e.g., pass messages) through the API 540.
- the application framework of one embodiment allows applications 610, 611 to be distributed across multiple PTEs 600 and 601, respectively.
- This embodiment may be particularly suited for multi-processor configurations (e.g., where each PTE 600, 601 is configured for a different processor).
- a common API is used for both inter- PTE and intra-PTE messaging.
- the common API allows an application to be configured to run in either a multiprocessor environment or on a single processor by merely altering a single routing configuration file (i.e., no changes to the application are required).
- tasks are defined as either "cooperative" tasks 730 or "preemptive” tasks 720.
- Cooperative tasks are composed exclusively of "cooperative" threads 731, 732 while preemptive tasks are composed exclusively of "preemptive" threads 721, 722.
- Cooperative tasks are defined as either "cooperative" tasks 730 or "preemptive” tasks 720.
- preemptive tasks 720 differ in their ability to provide shared memory pools and other resources 740 to their constituent threads. For example, threads
- Preemptive threads 721, 722 communicate externally (e.g., with an external message source and /or destination 705) only through message passing (e.g., via an API function call 710).
- all threads are individually configured to run at a specified priority level. It is not required that all threads in a task have the same priority (i.e., tasks may be composed of threads of differing priorities).
- a message for the thread is placed in a priority-sorted FIFO queue (e.g., such as the scheduling queue 215 illustrated in Figure 2). Normally, if the requested thread is a higher priority thread than the currently-running thread, the running thread is suspended (or "preempted") while the higher priority thread is executed. This operation is illustrated and described in Figures 8a through 8c.
- a preemptive thread In contrast to a cooperative thread, in one embodiment, the execution of a preemptive thread is not constrained by conditions other that its priority relative to other requested threads. Thus, if it is the highest priority requested thread, it is executed immediately.
- a PTE thread can exist in a variety of different states.
- idle state 910 a thread is inactive, waiting to be requested.
- a thread enters the requested state 920 when it receives a message from a running thread or an interrupt service routine ("ISR").
- ISR interrupt service routine
- the thread remains in the requested state until the requester terminates.
- the requested thread is either scheduled 940 or enters a "blocked" state 930 (depending on the circumstances as described herein).
- cooperative thread blocking is a built-in mutual exclusion mechanism required for memory sharing between cooperative threads running at different priority levels.
- a thread in a scheduled state 940 is queued, waiting for execution.
- Threads enter the scheduled state 940 after having been requested, after any blocking conditions have been cleared. Once scheduled, the thread cannot again be blocked. The thread will remain in the scheduling queue 940 until it is executed.
- the thread When running 950, the thread is performing the function for which it was designed. In one embodiment, only one thread may be running at a time. The thread will execute to completion unless it is preempted. The thread may enter into the preempted state 960 due to another higher priority thread(s) being scheduled (e.g., at the termination of an ISR).
- the PTE input queue (“QIN”) 1010 receives messages read from the external environment (i.e. other PTEs) and ISRs.
- the scheduler may route messages from QIN 1010 to the temporary task queue ("TTQ") 1060 and/or the priority scheduling queue ("PSQ") 1050.
- TTQ temporary task queue
- PSQ priority scheduling queue
- the PSQ 1050 includes a list of threads ready for immediate execution.
- the list is sorted based on scheduling variables such as, for example, thread priority and temporal order (i.e., the order in which the threads were requested).
- thread priority and temporal order i.e., the order in which the threads were requested.
- higher priority threads are executed before lower priority threads.
- thread requests requested earlier are run before threads requested later.
- Requests generated by a thread are stored in a temporary thread output queue ("TOQ") until the thread terminates. This ensures that a thread's output does not cause itself to be inadvertently preempted.
- TOQ temporary thread output queue
- a separate TOQ exists for each priority level. When a thread terminates its TOQ messages are distributed to the TTQ, the PSQ or the PTE output queue ("QOUT").
- the TTQ is a holding station for cooperative threads that have been requested but are not ready for scheduling because they are blocked by another active thread in their task group (as described above). This feature is necessary to ensure mutual exclusion between the members of a cooperative task with respect to the task's shared memory. In one embodiment, when the task's active thread terminates, the TTQ is emptied.
- the PTE Output Queue (“QOUT") is a temporary holder for all messages leaving the PTE. For example, the QOUT receives messages from the TOQ when a thread completes its execution.
- the scheduler When started, the scheduler initially sets the scheduler's priority variable (PRI) to the maximum priority level supported by the PTE.
- the scheduler (1110) reads any messages waiting for the PTE from external message sources (i.e. other possible PTEs) and copies (llll) these messages to the tail end of the PTE's input queue (QIN) in the order received. All messages (1115) in the PTE input queue (QIN) are then moved by the message routing function (1116) to either the Priority Scheduling Queue (PSQ) or to the Temporary Thread Queue (TTQ).
- PSQ Priority Scheduling Queue
- TTQ Temporary Thread Queue
- PTT corresponding to the current value of PRI (the scheduler's priority variable). If the PTT entry indicates that the priority level in "in use”, the scheduler exits immediately (1126) and resumes a preempted thread at the point where interrupted by an ISR.
- the scheduler examines the PSQ for any messages to threads with priority assignments equal to the scheduler's priority variable's value (1130). If none are found, PRI is decremented by one (1135) and if greater than zero (1120), the PTT (1125) is again examined for evidence of a preempted thread at a now lower thread priority level.
- the loop between 1120 to 1135 continues, thusly, until PRI is decremented to a negative value, in which case the scheduler exits (1121); PRI is decremented to the priority level of a previously preempted thread (1126), in which case the preempted thread is resumed (1126); or a message is found in the PSQ to a thread with a priority level equal to the value of PRI.
- scheduler If examination of the PSQ (1130) finds a message waiting for a thread with a priority level equal to that of PRI, scheduler alters the PTT's values to indicate that the priority level of corresponding to PRI is "in use”. The scheduler then extracts the message from the PSQ, starts the thread to which it is addressed (1131) and delivers the message to that thread.
- the scheduler routes each message (1140) created by the thread (found in the Thread Output Queue (TOQ) corresponding to the thread's priority level) to an appropriate message queues (PSQ, TTQ, or QOUT) as determined by the message router (1141).
- PSQ, TTQ, or QOUT message queues
- the TTQ is then scanned (1150) and messages therein are redistributed as determined by the message router (1151).
- each message (1160) in the output queue (QOUT) is distributed to an external PTE address by the PTE write function (1161) and the scheduler exits (1162).
- a routing function is implemented to route thread requests throughout the PTE (e.g., at each of the decision blocks of Figure 11).
- the scheduler in a critical section, may invoke the message routing function to move messages between the PTE's various message queues.
- the routing function in one embodiment uses the message's thread name as a destination address for the message (in this embodiment, each message contains a header with a thread name identifying its destination).
- the ultimate goal of the routing mechanism is to transfer a message from its source to a PSQ, and then to dispatch the message from the PSQ to the message's destination thread (e.g., specified by its thread name). To achieve this goal the router may pass the message through a series of intermediate queues (as described above).
- FIG. 12 One embodiment of a routing method is illustrated in Figure 12.
- the router de-queues the message from its source. Then, at 1230, the router determines whether the message is directed to an internal PTE thread or an external thread (i.e., located in a different PTE). If the destination is an external thread, then the router transfers the message to an output queue (at 1240) and the routing process is complete with respect to that message (i.e., the other PTE takes over the routing function after receiving the message from the output queue).
- the router determines whether the task is a preemptive task (at 1235). If the message is for a preemptive task, it transmits the message directly to the PSQ (at 1250) at a specified priority level. If the message is for a cooperative task, then at 1237 the router determines whether any other thread from the thread's task is preempted. If no other thread from the thread's task is preempted, the router transmits the message to the PSQ at a specified priority level (e.g., specified by the thread name as described below). If another thread from the thread's task is preempted, however, the router queues the message in the TTQ at the thread's specified priority level.
- a specified priority level e.g., specified by the thread name as described below
- the router uses three tables to look up information about its tasks and/or threads. As illustrated in Figures 13a, 13b and 13c, these include a thread attribute table (“TAT”), a task status table (“TST”), and/or a preempted thread table (“PTT”), respectively.
- TAT thread attribute table
- TST task status table
- PTT preempted thread table
- each thread in the PTE environment is uniquely identified by a thread "name.”
- Thread names may be used by the router to identify information such as, for example, a message's destination thread.
- the thread name e.g., "Thread[n]” in Figure 13a
- the thread name may be used to identify other information such as the thread's PTE, Task ID, Thread ID, Thread Priority, and Task Type.
- the task ID identifies the task to which the thread belongs.
- the task may be internal (i.e., within the local PTE) or external. If internal, messages sent to the task are delivered though internal message queues (as described above). If external, messages are routed to the common output queue ("QOUT").
- the thread ID identifies a specific thread within a task; the thread priority defines the thread's execution priority in relation to other threads (various priority levels may be implemented consistent with the underlying principles of the invention); and the task type identifies the thread's task as either preemptive or cooperative. It should be noted that although only one thread name entry is shown in Figure 13a, the underlying principles of the invention may be implemented using TAT's with a variety of different thread name entries.
- a task status table As indicated in Figure 13b, in one embodiment, a task status table
- TST records the priority of each task's highest priority started thread (in this context, "started” can mean running, preempted, or interrupted). If no thread within the task is running, the TST records that the task is idle.
- the scheduler uses the TST entries to route messages directed to started cooperative threads to the proper TTQ.
- the PTE keeps a table, referred to as a preempted thread table ("PTT”), that records the priority levels which are currently in use.
- PTT preempted thread table
- the PTE described herein is used to support a communications protocol stack.
- the protocol stack may be divided as illustrated in Figure 14, with the RF layer 1460 and portions of the baseband layer 1450 programmed in a Bluetooth IC 1406 (which may be an ASIC) and the remaining layers, including certain portions of the baseband layer 1450, implemented as software executed in the host processor environment 1405.
- tasks and threads may reside in both the Bluetooth IC 1406 and the host processing environment 1405.
- Each layer in the protocol stack is implemented as a separate task. Messages transmitted between tasks in the hardware portion and tasks in the software portion will occur over the host interface 1407.
- RFCOMM 1410
- L2CAP 1420
- PTE PTE Application Interface
- protocol layers RFCOMM and L2CAP in this case
- the PTE is ideal for this type of wireless communication environment because it can easily be ported from one host processing environment to another without significant modification.
- applications run within a PTE are composed of tasks (groups of threads) threads which interact with the PTE through a limited number of fixed API calls. Because the API calls are invariant for all PTE instances, a Task created for one PTE can be run on any other PTE without modification, regardless of the host environment. All differences in host environments are accounted for in the Host Adaptation Layer illustrated in Figures 3 and 4. It is typically be necessary to change only the Host Adaptation Layer when the PTE's host is changed.
- the PTE's simple common communication system for messaging and synchronization enable the PTE to be implemented with very little software in most operating environments. Being relatively small (and typically a small fraction of the size of i e application code it supports), the PTE can be adapted to a new host, and be proven to be operating correctly with relatively little effort. No other changes are necessary. It is important to note that the apparatus and method described herein may be implemented in environments other than a physical integrated circuit ("IC"). For example, the circuitry may be incorporated into a format or machine- readable medium for use within a software tool for designing a semiconductor IC.
- IC physical integrated circuit
- Examples of such formats and /or media include computer readable media having a VHSIC Hardware Description Language (“VHDL”) description, a Register Transfer Level (“RTL”) netlist, and/or a GDSII description with suitable information corresponding to the described apparatus and method.
- VHDL VHSIC Hardware Description Language
- RTL Register Transfer Level
- GDSII GDSII description with suitable information corresponding to the described apparatus and method.
- Figure 15 illustrates a finite state machine (FSM) 1500 built into the messaging structure of the PTE.
- FSM 1500 adds efficiency and uniformity to application developers in implementing software solutions utilizing the PTE.
- FSM 1500 changes states in response to events occurring outside of FSM 1500.
- FSM 1500 reduces the software needed to parse the PTE's message structure for determining the operation of the PTE.
- PTE messages 1501 are passed into FSM 1500.
- the previous state is provided to FSM 1500.
- FSM 1500 includes message interpreter 1520, which receives messages 1501 and determines if any actions need to be taken.
- An event field within PTE messages 1501 contains event information. Based on that event information and Previous State 1510, the message interpreter determines the actions to be performed by using a look-up table. The actions are stored in storage device 1540.
- State Changer 1580 may change the Previous State 1510 of the PTE or maintain the current state. State changer provides the generates new PTE messages from the stored actions.
- One or more FSM 1500's are implemented in a PTE cooperative task.
- FSM 1500 when a message is delivered to a thread, that thread may call FSM 1500 and passing to it the event received with the message. Any FSM state variables may be stored in the cooperative task's shared memory.
- FSM 1500 is well controlled by developers of portable software applications, is easily modifiable; and is easily debugged.
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AU2001259658A AU2001259658A1 (en) | 2000-05-08 | 2001-05-08 | A finite state machine in a portable thread environment |
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US20319200P | 2000-05-08 | 2000-05-08 | |
US60/203,192 | 2000-05-08 | ||
US09/792,550 US6961934B2 (en) | 2000-05-08 | 2001-02-23 | Portable thread environment |
US09/792,550 | 2001-02-23 |
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Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
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GB2429087A (en) * | 2005-08-10 | 2007-02-14 | Symbian Software Ltd | A method of operating a computer device through the use of extensible thread states |
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2001
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- 2001-05-08 WO PCT/US2001/014933 patent/WO2001086417A2/en active Search and Examination
Non-Patent Citations (5)
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"HTTP is Stateless" INTERNET DOCUMENT, [Online] 11 August 1998 (1998-08-11), XP002183341 Retrieved from the Internet: <URL:http://ipsec-wit.antd.nist.gov/newips ecdoc/stateless.html> [retrieved on 2001-11-02] & "Netscape - Page Info" NETSCAPE SCREENSHOT, 2 November 2001 (2001-11-02), XP002183342 * |
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THE DEBIAN PROJECT: "Debian GNU/Linux 2.1.11 (Slink)" SOFTWARE PROGRAM, [Online] 28 August 1999 (1999-08-28), Internet Retrieved from the Internet: <URL:http://www.debian.or/releases/slink/> [retrieved on 2001-10-26] & XAVIER LEROY <XAVIER.LEROYÐINRIA.FR>: "LinuxThreads Frequently Asked Questions (with answers) ÄFor LinuxThreads version 0.8] " INTERNET DOCUMENT, [Online] 26 October 1999 (1999-10-26), XP002138174 Retrieved from the Internet: <URL:http://pauillac.inria.fr/~xleroy/linu xthreads/faq.html> [retrieved on 2001-11-07] * |
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YUNG-CHEN HUNG, GEN-HUEY CHEN: "COMMUNICATION SYSTEM GENERATOR ON LAYERED COMMUNICATING FINITE STATE MACHINE" DISCOVERING A NEW WORLD OF COMMUNICATIONS. CHICAGO, JUNE 14 - 18, 1992, PROCEEDINGS OF THE INTERNATIONAL CONFERENCE ON COMMUNICATIONS, NEW YORK, IEEE, US, vol. 1, 14 June 1992 (1992-06-14), pages 466-470, XP000326910 ISBN: 0-7803-0599-X * |
Cited By (1)
Publication number | Priority date | Publication date | Assignee | Title |
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GB2429087A (en) * | 2005-08-10 | 2007-02-14 | Symbian Software Ltd | A method of operating a computer device through the use of extensible thread states |
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AU2001259658A1 (en) | 2001-11-20 |
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