Abstract:
Methods and apparatus for a cooperative processing of a task in a multi-threaded computing system are disclosed. In one aspect of the invention, a first thread is arranged to receive a task and only partially process the task. During its processing, the first thread stores processing information that is relevant to future processing in a packet that is associated with the task. Upon completing its processing, the first thread designates a second thread as the owner of the packet. After the second thread obtains ownership of the packet it then further processes the task based at least in part upon the processing information stored in the packet by the first thread. With the described arrangement no synchronization primitives are required for the threads to cooperate in processing the task.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The invention relates generally to methods and apparatus for cooperative processing of a task using multiple threads in a multi-threaded computing system. 
     2. Description of Relevant Art 
     In general, a thread is a sequence of central processing unit (CPU) instructions or programming language statements that may be independently executed. Each thread has its own execution stack on which method activations reside. As will be appreciated by those skilled in the art, when a method is activated with respect to a thread, an activation is “pushed” on the execution stack of the thread. When the method returns or is deactivated, the activation is “popped” from the execution stack. Since an activation of one method may activate another method, an execution stack operates in a first-in-last-out manner. 
     During the execution of an object-based program, a thread may attempt to execute operations that involve multiple objects. On the other hand, multiple threads may attempt to execute operations that involve a single object. Frequently, only one thread is allowed to invoke one of some number of operations, i.e., synchronized operations, that involve a particular object at any given time. That is, only one thread may be allowed to execute a synchronized operation on a particular object at one time. A synchronized operation, e.g., a synchronized method, is block-structured in that it requires that the thread invoking the method to first synchronize with the object that the method is invoked on, and desynchronize with that object when the method returns. Synchronizing a thread with an object generally entails controlling access to the object using a synchronization primitive before invoking the method. 
     Since multiple threads must work together on a shared data resource, there must be a mechanism for preventing these threads from destroying data integrity by, for example, writing at the same time to a particular data area. This particular problem has been solved by using synchronization primitives such as locks, mutexes, semaphores, and monitors to control access to shared resources during periods in which allowing a thread to operate on shared resources would be inappropriate. By way of example, in order to prevent more than one thread from operating on an object at any particular time, objects are often provided with locks. The locks are arranged such that only the thread that has possession of the lock for an object is permitted to execute a method on that object. 
     As previously mentioned, a thread is permitted to execute a synchronized operation on an object if it successfully acquires the lock on the object. While one thread holds the lock on an object, other threads may be allowed to attempt to execute additional synchronization operations on the object, and may execute non-synchronized operations on the object. Thread synchronization is a process by which threads may interact to check the status of objects, whether the objects are locked or unlocked, while allowing only the thread which holds an object lock to execute synchronized operations on the locked object. Thread synchronization also enables threads to obtain and remove object locks. 
     In recent years significant efforts have been made to facilitate the creation of platform independent software. That is, software that can execute on multiple different platforms (e.g., different types of computer systems), without requiring the software program to be rewritten or customized to operate on specific platforms. By way of example, the Java programming language is designed to facilitate the creation of Java software objects that are platform independent. Platforms that support Java and a number of other programming languages, require native threads to cooperate with platform independent threads. 
     Since platform independent threads, such as Java, are subject to potentially long delays they are generally not designed to run time critical code. That task is left to native threads since they typically are capable of quickly reacting to and processing tasks where timely completion is important. By way of example, native code is used to process an interrupt asserted by, for example, a serial device whose buffer may overrun if not handled fast enough. If, for example, the serial device interrupt was handled by a Java thread, too much latency would accrue in those situations when the Java thread is held off from running. If the Java thread was held off long enough, the delay in processing the serial device interrupt could potentially cause an device error. 
     One situation where a Java thread is held off from running is referred to as garbage collection. Typical of a Java Virtual Machine (JVM), garbage collection is a process whereby inactive, or otherwise unneccessary objects and/or threads, are identified, collected, and deactivated. In a typical object based computing system, all platform independent threads are kept from running for at least the duration of the garbage collection process. 
     An additional problem related to those situations where platform independent and native threads do not cooperate occurs in those situations where a Java thread holds ownership of a synchronization primitive (such as a mutex, lock, semaphore, etc.) just prior to being suspended during, for example, the initiation of garbage collection. In this situation, the Java thread cannot relinquish ownership of the synchronization primitive for at least the duration of garbage collection. Consequently, the native thread cannot obtain ownership of the particular synchronization primitive owned by the Java thread and is thereby prevented accessing a locked resource thereby preventing the native thread from running time critical execution of code during garbage collection. 
     In view of the foregoing, it should be apparent that improved mechanisms and frameworks for cooperative execution of a task using multiple threads in a multi-threaded computer system would be desirable. 
     SUMMARY OF THE INVENTION 
     To achieve the foregoing and other objectives, improved mechanisms for cooperatively processing a task in a multi-threaded computer system are described. In one aspect of the invention, a first thread is arranged to receive a task and only partially process the task. During its processing, the first thread stores processing information that is relevant to future processing in a packet that is associated with the task. Upon completing its processing, the first thread designates a second thread as the owner of the packet. After the second thread obtains ownership of the packet it then further processes the task based at least in part upon the processing information stored in the packet by the first thread. With the described arrangement no synchronization primitives are required for the threads to cooperate in processing the task. 
     In some embodiments, additional threads also participate in the cooperative processing of the task. By way of example, in an embodiment having three threads that cooperatively process the task, the second thread stores additional processing information in the packet and designates a third thread as the owner of the packet upon completion of its processing. The third thread then further processes the task after it obtains ownership of the packet, based at least in part upon the processing information stored in the packet by the second thread. 
     In some preferred embodiments, designating ownership of the packet is accomplished by updating an ownership field included in the packet. In this arrangement, each thread that participates in the processing of the task sets the ownership of the packet to the next thread to process the task and the final thread to process the task sets the ownership of the packet to no owner. 
     In a described embodiment, the task is interrupt handling, the threads execute different order interrupt handlers and the packet is an interrupt packet. 
     In another aspect of the invention an improved interrupt handling system is described. The interrupt handling system includes an interrupt packet and an interrupt handler that is divided into a plurality of different order interrupt handling components. The interrupt handling components are arranged to cooperatively process an interrupt in a serial fashion. An interrupt packet that is accessible by the plurality of different order interrupt handling components and is arranged to pass processing information between interrupt handling components. 
     In some embodiments, the interrupt packet includes an owner field arranged to store data indicative of the interrupt handling component that currently owns the interrupt packet. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention, together with further advantages thereof, may best be understood by reference to the following description taken in conjunction with the accompanying drawings. 
     FIG. 1 illustrates a device driver in accordance with an embodiment of the invention. 
     FIG. 2 illustrates a particular relationship between interrupt handlers defined by the device interrupt source object in accordance with an embodiment of the invention. 
     FIGS. 3A and 3B illustrates different aspects of an interrupt packet in accordance with an embodiment of the invention. 
     FIG. 4A illustrates a message passing scheme between interrupt handlers in accordance with an embodiment of the invention. 
     FIG. 4B illustrates processing of the interrupt INT 1  shown in FIG.  4 A. 
     FIG. 5 is a flowchart detailing a possible process for handling device interrupts by a lowest order interrupt handler in accordance with an embodiment of the invention. 
     FIG. 6 is a flowchart detailing a possible process for handling device interrupts by a higher order interrupt handler in accordance with an embodiment of the invention. 
     FIG. 7 is a flowchart detailing a possible process for getting a next interrupt packet in accordance with an embodiment of the invention. 
     FIG. 8 is a flowchart detailing a process for sending a next interrupt packet in accordance with an embodiment of the invention. 
     FIG. 9 shows a ring buffer in accordance with an embodiment of the invention. 
     FIG. 10 is a representative computer system in accordance with an embodiment of the invention. 
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     In the following description frameworks and methods of cooperatively processing a task by multiple threads in a multi-threaded computer system are described. In general, upon receipt of a packet associated with the task, a first thread partially processes the task. The packet is then passed from the first thread to a second thread that, upon receipt of the packet, further processes the task. Since only the thread currently possessing the packet can process the task, no synchronization primitives, such as mutexes, are required for the threads to cooperate with each other. 
     The invention will initially be described in terms of an interrupt handler for a device driver. The interrupt handler itself is conceptually divided into a plurality of different order handlers. The tasks that are to be handled by the interrupt handler are also divided into various segments with each order interrupt handler being designed to handle an associated segment of the overall task. The tasks can conceptually be organized in any appropriate manner, however, in the context of an interrupt handler it is typically most logical to divide the activities by their relative priority. More specifically, it should be appreciated that some of the activities performed by an interrupt handler may be very time critical and must be handled as quickly as possible, while other tasks are not particularly time critical and may effectively be handled on a less time critical basis. The various order handlers are arranged to partition the work performed by the interrupt handler such that the most time critical activities are handled by the order-1 interrupt handler. Less time critical, but still high priority tasks are handled by the order-2 interrupt handler. The least time critical tasks are handled by the order-3 handler. Of course, a task could readily be broken into more or less segments based on the nature of the task being handled. 
     In the described embodiment, the order-1 interrupt handler is designed to perform tasks that are deemed to require the use of a micro-kernal thread. These are generally the tasks that are considered to be the most time critical. The order-2 interrupt handler is designed to perform tasks that are deemed to require the use of a high priority system thread (higher than a non-native thread and any other system thread). Thus, tasks that are considered to be very important, but not as time critical as the order-1 tasks are handled by the order-2 interrupt handler. The order-3 interrupt handler is arranged to run non-native threads and to perform the tasks that are not particularly time critical. 
     FIG. 1 illustrates a device driver  100  that may benefit from cooperative task processing performed in accordance with an embodiment of the invention. As will be appreciated by those skilled in the art, a device driver is a program written to support an associated device. In computer systems, devices supported by a device driver may include, but are not limited to input and output devices such as printers, monitors, modems and/or network/telephone connections. The device driver  100  illustrated in FIG. 1 includes an interrupt handler  102  arranged to process hardware interrupts generated by the device that the device driver  100  is managing. The interrupt handler is partitioned into a plurality of sub-parts, including an order-1 interrupt handler  106 , an order-2 interrupt handler  108 , and an order-3 interrupt handler  110 . In alternative embodiments, any combination of these and other orders may be defined for a particular interrupt handler. In the illustrated embodiment, A device interrupt source  104  is provided which defines the particular interrupt handlers used by and associated with the device driver  100 , such as, for example, the interrupt handler  102 . 
     FIG. 2 illustrates a particular relationship  200  between the various interrupt handlers defined by the device interrupt source  104  in accordance with an embodiment of the invention. In the described embodiment, the order-1 interrupt handler  106  is invoked at  206  in the context of a microkernal interrupt handler  202  included in a microkernal  201  well known by those skilled in the art. The microkernal interrupt handler  202  is software that immediately begins running whenever hardware coupled to the microkernal  201  asserts an interrupt. It is important to note, however, that once the microkernal interrupt handler  202  begins to run, any thread that is currently running in the multi-threaded computer system is immediately suspended. It should also be noted, that once the microkernal interrupt handler  202  returns, a microkernal scheduler  204  (i.e., software used to schedule prioritized threads) un-suspends the highest priority thread even though that thread may or may not be the thread that was interrupted. In one embodiment, the order-1 handler  206  runs native code (i.e., platform dependent code) and subsequently fulfills the most immediate needs of the interrupting device such as, for example, when the interrupting device is a serial device whose buffer may overrun if not handled fast enough. 
     It should be noted that while the order-1 handler  106  is running, all further interrupts from the interrupting device are masked. After the microkernal interrupt handler  202  calls the order-1 interrupt handler  106  and the order-1 interrupt handler  106  returns (if it is the lowest order handler), or after the microkernal interrupt handler  202  signals the order-2 interrupt handler  108  or order-3 interrupt handler  110  (whichever is lowest), the microkernal interrupt handler  202  transfers control to the microkernal scheduler  204 . 
     All hardware interrupts are for a particular level, and a higher hardware level will pre-empt an interrupt currently being processed at a lower level. For example, if an order-1 interrupt handler is currently running for a level-3 hardware interrupt, and an interrupt for a level 4 occurs, that level 4 interrupt will pre-empt the order-1 handler running for the level-3 interrupt. 
     In addition, the running order-1 interrupt handler  106  also preempts other order-1 interrupt handlers coupled to the microkernal  201  that were invoked by the lower-level microkernal interrupt handler  202  as well as any non-native threads (i.e., platform independent threads such as Java threads). It is for at least this reason that the order-1 interrupt handler  106  should do the absolute minimum that is necessary to satisfy the most immediate needs of the interrupting device and leave the remainder of interrupt handling for higher-order interrupt handlers (such as the order-2 and order-3 interrupt handlers). It is important to note that in those situations where non-native threads, such as Java, are suspended during, for example, garbage collection, the order-1 interrupt handler  106  is still capable of running. In this way, time critical processes are still capable of being run. 
     In the described embodiment, the order-2 interrupt handler  108  is, in some cases, signaled from the order-1 interrupt handler at  208 . In those cases where no order-1 interrupt handler exists, the order-2 interrupt handler  108  is signaled from the microkernal interrupt handler  202  at  210 . In a preferred embodiment, the order-2 interrupt  108  handler runs native code in a high priority system thread (higher than a non-native thread and any other system thread) and performs additional interrupt handling. Since the order-2 interrupt handler  108  runs native code (platform dependent), and since it has higher priority than any other non-native thread, the order-2 interrupt handler  108  can handle real time needs of the interrupting device. At the same time, unlike the order-1 interrupt handler  106 , the order-2 interrupt handler  108  can continue interrupt processing without masking additional interrupts from the interrupting device. An interrupt can still occur, and the order-1 interrupt handler  106  can run while the order-2 interrupt handler  108  is in the middle of interrupt handling. Once the order-2 interrupt handler  108  finishes its interrupt handling, it signals the order-3 interrupt handler  110  at  212 . It is important to note that the order-2 interrupt handler  108  should be able to run while the non-native threads are suspended during, for example, garbage collection. 
     In addition to the order-1 interrupt handler  106  and the order-2 interrupt handler  108 , the device interrupt source  104  is arranged to define the order-3 interrupt handler  110 . The order-3 interrupt handler  110  is signaled to run from either the order-2 interrupt handler  108  or the order-1 interrupt handler  106  at  214  in the case where there is no order-2 interrupt handler. However, if there is neither an order-1 interrupt handler nor an order-2 handler present, the signaling can come from the microkernal interrupt handler  202  directly at  216 . 
     It is important to note that in the described embodiment, the order-3 interrupt handler  110  runs non-native code, such as Java, exclusively and for this reason can be especially slow when it is pre-empted for long periods such as when the non-native threads are suspended. For this reason, the order-3 interrupt handler  110  should not be used for time critical interrupt processing. In addition, since the order-3 interrupt handler  110  is the only interrupt handler capable of running non-native code, such as Java, the device interrupt source  104  must define the interrupt handler  104 , as a minimum, to include the order-3 interrupt handler  110  in those situations where non-native threads are contemplated. 
     Typically, the number and type of interrupt handlers defined by the device interrupt source  104  is determined by the particular application as well as the number and type of hardware devices. In those situations where the delay experienced by native threads when non-native threads are suspended is not significant or doesn&#39;t cause significant system performance problems, the device interrupt source  104  may find it necessary to only allocate the order-3 interrupt handler  110 . On the other hand, in those situations where it is imperative that native threads be left to run substantially unhindered (even though non-native threads are suspended for reasons such as garbage collection) it is important to allocate more of the lower order interrupt handlers. By way of example, the device interrupt source  104  can allocate relatively more of the order-1 interrupt handlers  106  and/or the order-2 interrupt handlers  108  in than of the order-3 handlers  110  when running time critical processes without substantial hindrance is important. 
     Referring again to FIG. 1, in one embodiment of the invention, when the device interrupt source  104  is instantiated, an interrupt packet  112  is allocated. In the described embodiment, the actual number of interrupt packets  112  is determined by the device driver  100  based upon particular requirements of the device being managed. It should be noted that based upon these requirements, the device interrupt source  104  can allocate a pool of interrupt packets  114  represented by interrupt packets  112   a - 112   d.    
     FIGS. 3A and 3B illustrates different aspects of an interrupt packet  300  in accordance with an embodiment of the invention. It should be noted that the interrupt packet  300  is one particular implementation of the interrupt packet  112 . In a preferred embodiment, the interrupt packet  300  contains a protected owner field  302  that takes on a value indicative of current ownership of the interrupt packet  300 . The interrupt packet  300  also includes a processing data field  303  used to store relevant task processing information. 
     Table 1 lists representative owner field values and associated ownership status according to one embodiment of the invention. 
     
       
         
               
               
             
           
               
                 TABLE 1 
               
               
                   
               
               
                 Owner Field Value 
                 Status 
               
               
                   
               
             
             
               
                 0 
                 free (not currently owned 
               
               
                   
                 by any interrupt handler) 
               
               
                 1 
                 owned by the order-1 interrupt handler 
               
               
                 2 
                 owned by the order-2 interrupt handler 
               
               
                 3 
                 owned by the order-3 interrupt handler 
               
               
                   
               
             
          
         
       
     
     By way of example, if the owner field  302  has a value of “0”, as indicated by Table 1, the interrupt packet  300  is un-owned (i.e., no interrupt handler currently owns the interrupt packet  302 ). Alternatively, if the owner field  302  has a value of “1”, as indicated by Table 1, the interrupt packet  300  is owned by the order-1 handler  106 . It should be noted that, in a preferred embodiment, when the device interrupt source object  102  is instantiated, all corresponding interrupt packets  112   a - 112   d  are allocated with their respective owner fields set to 0 indicating that no interrupt handler currently owns the particular interrupt packet. 
     In the described embodiment, the interrupt packet  300  can be extended to include information in addition to the current owner. By extended, it is meant that additional data fields containing information specific to the particular device the associated device driver manages for example, are added. By way of example, the interrupt packet  300  can be extended to include additional data fields associated with, for example, financial data particularly useful for specific financial applications and associated devices. Such an interrupt packet  304  is shown in FIG.  3 B. The interrupt packet  304  includes an owner field  306  and a processing data field  307 . For this example, the interrupt packet  304  has been extended to include additional data fields  308  used, for example, in defining particular application specific data depending upon the particular native application for which the additional data fields  308  are associated. 
     It is important to note that since the native operating system only interacts with the owner field, the presence of additional data fields in the extended interrupt packet  304  is irrelevant to the execution of the native operating system. It is for at least this reason, that any extension of an interrupt packet by a particular application leaves the interrupt packet platform independent. 
     Since the order-1, order-2, and order-3 interrupt handlers for a particular device driver can handle interrupts concurrently it is necessary to avoid any synchronization problems. Such problems caused by, for example, garbage collection result in native threads being suspended. In one embodiment of the invention, such synchronization problems are avoided by using an efficient message passing approach. In a preferred embodiment, the efficient message passing utilizes the interrupt packets  112  provided by the device interrupt source  104 . During operation, when an interrupt handler (of any order) exclusively processes an interrupt, it stores processing information relevant to the interrupt processing in the interrupt packet  112 . When a particular interrupt handler has completed its processing of the interrupt and is ready to hand the processing off to a higher order interrupt handler (i.e., from the order-1 interrupt handler  106  to the order-2 interrupt handler  108 , for example), the lower order interrupt handler passes the interrupt packet to the higher order interrupt handler. The higher order handler then appropriately updates the interrupt packet and continues to process the interrupt. Since no two interrupt handlers possess the same interrupt packet at the same time, synchronization is unnecessary. 
     By way of example, FIG. 4A illustrates a scheme  400  for cooperatively processing an interrupt in accordance with an embodiment of the invention. For this example, the device driver  100  includes an order-1 interrupt handler  406  as well as an order-3 interrupt handler  408  (required to run non-native code) instantiated by the device interrupt source  104 . When the interrupt INT 1  is asserted, the microkernal handler  202  suspends all native threads until such time as it sends an interrupt packet  410  to the order-1 interrupt handler  406 . It should be noted that while in possession of the microkernal handler  202 , the owner field  412  of the interrupt packet  410  has a value of “0” indicating that it is un-owned. 
     Once the microkernal handler  202  has sent the interrupt packet  410  to the order-1 interrupt handler  406 , the owner field  412  of the interrupt packet  410  is updated to a value of “1” indicating that it is now owned by the order-1 handler  406 . Since the order-1 interrupt handler  406  currently owns the interrupt packet  410 , it is now the only interrupt handler included in the device driver  100  enabled to process the interrupt INT 1 . It should be noted as well, that any additional interrupts asserted while the order-1 interrupt handler  406  is processing the interrupt INT 1  are masked until such time as the interrupt packet  410  is passed along to a higher order interrupt handler. In this case, even if the non-native code is suspended, the order-1 interrupt handler  406  is still able to process time critical native threads since it alone owns the interrupt packet  410 . 
     Assuming at a time Δt 0  subsequent to the completion of either order-1 interrupt handling (if there is one) or signaling of what is otherwise the lowest order interrupt handler of the interrupt INT 1  another interrupt INT 2  is asserted. As described above, the interrupt INT 2  is masked until the order-1 interrupt handler  406  sends the interrupt packet  410  to a higher order interrupt handler, such as the order-3 interrupt handler  408 . Therefor, in order for the order-1 interrupt handler  406  to process the interrupt INT 2 , it must send the interrupt packet  410  to the order-3 interrupt handler  408 . 
     Once the order-1 interrupt handler  406  sends the interrupt packet  410  to the order-3 interrupt handler  408 , it gets a new interrupt packet  414  from the microkernal interrupt handler  202  in order to process the newly asserted (and heretofore masked) interrupt INT 2 . 
     It should be noted that the owner field  412  of the interrupt packet  410  has been updated to a value of “3” indicating that it is now owned by the order-3 interrupt handler and that the owner field  416  of the interrupt packet  414  is updated to a value of “1”. In this configuration, the remainder of the interrupt INT 1  can be processed by the order-3 interrupt handler  408  concurrently with the interrupt INT 2  being processed by the order-1 interrupt handler  406 . If an occasion arises where the order-3 interrupt handler is suspended for any reason unrelated to the native operating system, time critical native threads can still be processed by the order-1 interrupt handler  406  after it has completed its processing of the interrupt INT 2 . 
     FIG. 4B illustrates processing of the interrupt INT 1  shown in FIG.  4 A. For this example, the interrupt INT 1  includes a series of tasks identified as  1 ,  13 , 18 , D 3 , E 3 , which must be completed in order for the interrupt INT 1  to be considered fully processed. It should be noted that “A1” refers to the process “A” being performed by the order-1 handler  406  whereas “C3” refers to the process “C” being performed by the order-3 handler  408 , and so on. Therefor, the order-1 interrupt handler  406  will process tasks “A” and “B” quickly, since, at least for this example, they represent time critical processes. Whereas, when the interrupt packet  410  is passed to the order-3 interrupt handler  508 , the tasks “C”, “D”, and “E”, are processed by the order-3 interrupt handler  408 . In this way, the interrupt INT 1  is fully processed by the cooperative effort of the order-1 interrupt handler  406  and the order-3 interrupt handler  408  as mediated by the interrupt packet  410  that is associated with the interrupt INT 1  only. It should be noted that the same procedure is followed for the cooperative processing of the interrupt INT 2 . 
     A particular implementation of the invention will now be described with reference to FIGS. 5-8. 
     FIG. 5 is a flowchart detailing a possible process  500  for handling device interrupts by a lowest order interrupt handler in accordance with an embodiment of the invention. The process  500  begins at  502  when a device driver receives an interrupt from the device it is managing. Once the interrupt is received, the device driver calls a get_next_packet function at  504 . Once the get_next packet function has been completed the get_next_packet is passed the order of the interrupt handler that wants the next packet and the fetched interrupt packet is passed to the lowest order handler at  506 . By way of example, if the device driver includes an order-1 interrupt handler and an order-3 interrupt handler, then the interrupt packet is passed to the order-1 interrupt handler. Alternatively, if the device driver has only an order-3 interrupt handler, then the interrupt packet is passed from the microkernal directly to the order-3 handler. Once the interrupt packet has been passed to the lowest order interrupt handler, the interrupt handler processes the interrupt packet by, in one embodiment, storing appropriate lowest order state information in the interrupt packet at  508 . Such state information includes information related to processing the interrupt associated with the interrupt packet. A particular example relates to a serial device driver having an array of characters that are read out of some hardware register by an order-1 interrupt handler. The order-1 interrupt handler in this case processes only these characters while the order-2 and order-3 interrupt handlers do further processing of the state information. A determination at  510  is then made regarding whether or not the interrupt packet is ready to be passed on. By passed on, it is meant that the interrupt packet is ready to be sent to the next interrupt handler. 
     If the determination at  510  is that the interrupt packet is ready to be passed on, then the device driver calls a send_packet function at  512 . After the send_packet function has been completed, the process  500  waits at  514  for a next interrupt from the device being managed by the device driver. Alternatively, if it was determined at  510  that the interrupt packet was not ready to be passed on, then control is passed to  514  without calling the send_packet function until such time as a next interrupt is received from the device being managed by the device driver. 
     FIG. 6 is a flowchart detailing a possible process  600  for handling device interrupts by a higher order interrupt handler in accordance with an embodiment of the invention. It should be noted that the process  600  is used in conjunction with the process  500  in those situations where interrupt handlers of more than one order have been instantiated. The process  600  begins at  602  by calling the get_next_packet function. Once the next packet has been obtained, the packet is passed to an associated higher order interrupt handler which further processes the packet, by for example, storing appropriate state data in appropriate data fields at  604 . At  606 , it is then determined whether or not the packet is ready to be passed on. If it is determined that the packet is not ready to be passed on, control is returned to  602  where the next packet function is called. On the other hand, if the packet is ready to be passed on, then the packet is passed on to a next appropriate interrupt handler by calling the send_packet function at  608 . 
     FIG. 7 is a flowchart detailing a possible process  700  for getting a next interrupt packet in accordance with an embodiment of the invention. It should be noted that the process  700  is one particular implementation of the get_next_packet function at  504  of the process  500 . The process  700  begins at  702  by a determination of whether or not an unsent interrupt packet exists for the current interrupt handler. If it is determined that there is an unsent interrupt packet, then the unsent interrupt packet is returned to the calling interrupt handler at  704 . If, however, it is determined that there is no unsent interrupt packet, then the next interrupt packet for the calling interrupt handler is identified at  706 . Once the next interrupt packet is identified, a determination at  708  is made whether or not the identified interrupt packet is owned by the calling interrupt handler. If it is determined that the identified next interrupt packet does not belong to the calling interrupt handler, then the process waits at  710  for the identified next interrupt packet to be assigned to the calling interrupt handler. If, however, it was determined at  708  that the identified next interrupt packet is owned by the calling handler, then the identified next interrupt packet is returned at  712 . It should be noted, that in one implementation of the invention, an array of state variables is used. 
     FIG. 8 is a flowchart detailing a process  800  for sending a next interrupt packet in accordance with an embodiment of the invention. It should be noted that the process  800  is a particular implementation of the send_next_packet function at  508  of the process  500 . The process  800  begins at  802  by setting an unsent packet flag in the interrupt packet to null indicating that there are no unsent packets. At  804 , the current owner of the packet is set to a value corresponding to the next highest order handler available (which now becomes the current handler). At  806 , a determination is made whether or not the current handler is now the highest order handler. If the current handler is now the highest order handler, then the process  800  stops. Otherwise, the next highest order handler available is notified at  808  after which the process  800  stops. 
     In one embodiment of the invention, the get_next_packet function and the send_next_packet function taken together manage the array of interrupt packets. In one particular implementation, the interrupt packets are managed as a ring buffer. One such ring buffer is configured in such a way that after a particular order interrupt handler has processed, for example, an interrupt packet p, the next interrupt packet that the particular interrupt handler will process is always the interrupt packet identified by the relation: 
     
       
         (p+1)(modulo N), 
       
     
     where N is the total number of interrupt packets. 
     Such a ring buffer arrangement is shown in FIG. 9. A ring buffer  902  contains 4 interrupt packets arranged between an order-1 handler, an order-2 handler, and order-3 handler, and as unowned. 
     Although only a few embodiments of the present invention have been described, it should be understood that the present invention may be embodied in many other specific forms without departing from the spirit or the scope of the present invention. Steps may also be removed or added without departing from the spirit or the scope of the present invention. 
     FIG. 10 illustrates a computer system  1000  in accordance with an embodiment of the invention. The computer system  1000  includes a central processing unit (“CPU”)  1002 , such as, for example, a Sun Microsystems SPARC, Motorola PowerPC, or Intel Pentium processor. CPU  1002  is coupled with a memory  1004  that includes any type of memory device used in a computer system, such as for example, random access memory (“RAM”) and read-only memory (“ROM”). CPU  1002  is also coupled with a bus  1006 , such as a PCI bus, or an S bus. A variety of input devices  1008  and  1010 , and output devices  1012  are also coupled with bus  1006 . Examples of such input and output devices include, but are not limited to, printers, monitors, modems, and/or network/telephone connections. Typically each of these devices has an associated with it a device driver. A device driver is an object-oriented program written to support an associated device coupled with computer system  1000 . By way of example, the device driver  114  manages the input device  1008 . Likewise, other device drivers can be utilized to support and manage any device, such as devices  1010  and  1012 , coupled to the computer system  1000 . 
     Although the methods of cooperative execution of native and non-native threads in a multi-threaded system in accordance with the present invention are particularly suitable for implementation with respect to a Java based environment, the methods may generally be applied in any suitable object-based environment. In particular, the methods are suitable for use in platform-independent object-based environments. It should be appreciated that the methods may also be implemented in some distributed object-oriented systems. 
     While the present invention has been described as being used with a computer system that has an associated virtual machine, it should be appreciated that the present invention may generally be implemented on any suitable object-oriented computer system. Specifically, the methods of passing interrupt packets with the present invention may generally be implemented in any multi-threaded, object-oriented system without departing from the spirit or the scope of the present invention. Therefore, the present examples are to be considered as illustrative and not restrictive, and the invention is not to be limited to the details given herein, but may be modified within the scope of the appended claims along with their full scope of equivalents.