Classifications

• • 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
  • G06F9/52—Program synchronisation; Mutual exclusion, e.g. by means of semaphores
• • 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
  • G06F9/30—Arrangements for executing machine instructions, e.g. instruction decode
• • G—PHYSICS
  • G06—COMPUTING; CALCULATING OR COUNTING
  • G06F—ELECTRIC DIGITAL DATA PROCESSING
  • G06F15/00—Digital computers in general; Data processing equipment in general
  • G06F15/16—Combinations of two or more digital computers each having at least an arithmetic unit, a program unit and a register, e.g. for a simultaneous processing of several programs

Definitions

• the present invention relates to computers and, in particular, to a modified machine architecture which enables the operation of an application program simultaneously on a plurality of computers interconnected via a communications network.
• Fig. 1 that single prior art machine 1 is made up from a central processing unit, or CPU, 2 which is connected to a memory 3 via a bus 4. Also connected to the bus 4 are various other functional units of the single machine 1 such as a screen 5, keyboard 6 and mouse 7.
• a fundamental limit to the performance of the machine 1 is that the data to be manipulated by the CPU 2, and the results of those manipulations, must be moved by the bus 4.
• the bus 4 suffers from a number of problems including so called bus
• a single application program (Ap) is partitioned by its author (or another programmer who has become familiar with the application program) into various discrete tasks so as to run upon, say, three machines in which case n in Fig. 3 is the integer 3.
• the intention here is that each of the machines Ml ...M3 runs a different third of the entire application and the intention is that the loads applied to the various machines be approximately equal.
• the machines communicate via a network 14 which can be provided in various forms such as a communications link, the internet, intranets, local area networks, and the like. Typically the speed of operation of such networks 14 is an order of magnitude slower than the speed of operation of the bus 4 in each of the individual machines Ml, M2, etc.
• Distributed computing suffers from a number of disadvantages. Firstly, it is a difficult job to partition the application and this must be done manually. Secondly, communicating data, partial results, results and the like over the network 14 is an administrative overhead. Thirdly, the need for partitioning makes it extremely difficult to scale upwardly by utilising more machines since the application having been partitioned into, say three, does not run well upon four machines. Fourthly, in the event that one of the machines should become disabled, the overall performance of the entire system is substantially degraded.
• a further prior art arrangement is known as network computing via “clusters" as is schematically illustrated in Fig. 4.
• the entire application is loaded onto each of the machines Ml , M2 ....Mn.
• Each machine communicates with a common database but does not communicate directly with the other machines.
• each machine runs the same application, each machine is doing a different "job” and uses only its own memory. This is somewhat analogous to a number of windows each of which sell train tickets to the public.
• This approach does operate, is scalable and mainly suffers from the disadvantage that it is difficult to administer the network.
• the present invention discloses a computing environment in which an application program operates simultaneously on a plurality of computers. In such an environment it is necessary to ensure that the "monitor enter” and “monitor exit” (more generally synchronization routines) operate in a consistent fashion across all the machines. It is this goal of consistent locking of resources that is the genesis of the present invention.
• a method multiple computer system having at least one application program running simultaneously on a plurality of computers interconnected by a communications network, wherein a like plurality of substantially identical objects are created, each in the corresponding computer and each having a substantially identical name, and said system including a lock means applicable to all said computers wherein any computer wishing to utilize a named object therein acquires an authorizing lock from said lock means which permits said utilization and which prevents all the other computers from utilizing their corresponding named object until said authorizing lock is relinquished.
• a plurality of computers interconnected via a communications link and operating at least one application program simultaneously wherein each said computer in operating said at least one application program utilizes an object only in local memory physically located in each said computer, the contents of the local memory utilized by each said computer is fundamentally similar but not, at each instant, identical, and every one of said computers has a an acquire lock routine and a release lock routine which permit utilization of the local object only by one computer if each of the remainder of said plurality of computers is locked out of utilization of their corresponding object.
• a multiple thread processing computer operation in which individual threads of a single application program are simultaneously being processed each on a corresponding one of a plurality of computers interconnected via a communications link, and in which objects in local memory physically associated with the computer processing each thread have corresponding objects in the local memory of each other said computer, the improvement comprising permitting only one of said computers to utilize an object and preventing all the remaining computers from simultaneously utilizing their corresponding object.
• a computer program product comprising a set of program instructions stored in a storage medium and operable to permit a plurality of computers to carry out the abovementioned methods.
• Fig. 1 is a schematic view of the internal architecture of a conventional computer
• Fig. 2 is a schematic illustration showing the internal architecture of known symmetric multiple processors
• Fig. 3 is a schematic representation of prior art distributed computing
• Fig. 4 is a schematic representation of a prior art network computing using clusters
• Fig. 5 is a schematic block diagram of a plurality of machines operating the same application program in accordance with a first embodiment of the present invention
• Fig. 6 is a schematic illustration of a prior art computer arranged to operate JAN A code and thereby constitute a JAVA virtual machine
• Fig. 7 is a drawing similar to Fig.
• Fig. 8 is a drawing similar to Fig. 5 but illustrating the interconnection of a plurality of computers each operating JANA code in the manner illustrated in Fig. 7,
• Fig. 9 is a flow chart of the procedure followed during loading of the same application on each machine in the network
• Fig. 10 is a flow chart showing a modified procedure similar to that of Fig. 9
• Fig. 11 is a schematic representation of multiple thread processing carried out on the machines of Fig. 8 utilizing a first embodiment of memory updating
• Fig. 12 is a schematic representation similar to Fig. 11 but illustrating an alternative embodiment
• Fig. 13 illustrates multi-thread memory updating for the computers of Fig. 8, Fig.
• FIG. 14 is a schematic illustration of a prior art computer arranged to operate in JANA code and thereby constitute a JANA virtual machine
• Fig. 15 is a schematic representation of n machines nmning the application program and serviced by an additional server machine X
• Fig. 16 is a flow chart of illustrating the modification of the monitor enter and exit routines
• Fig. 17 is a flow chart illustrating the process followed by processing machine in requesting the acquisition of a lock
• Fig. 18 is a flow chart illustrating the requesting of the release of a lock
• Fig. 19 is a flow chart of the response of the server machine X to the request of Fig. 17,
• Fig. 20 is a flow chart illustrating the response of the server machine X to the request of Fig. 18, Fig.
• FIG. 21 is a schematic representation of two laptop computers interconnected to simultaneously run a plurality of applications, with both applications running on a single computer
• Fig. 22 is a view similar to Fig. 21 but showing the Fig. 21 apparatus with one application operating on each computer
• Fig. 23 is a view similar to Figs. 21 and 22 but showing the Fig. 21 apparatus with both applications operating simultaneously on both computers.
• Annexures A and D which provide actual program fragments which implement various aspects of the described embodiments.
• Annexure A relates to fields and Annexure D to synchronization.
• a single application program 50 can be operated simultaneously on a number of machines Ml, M2...Mn communicating via network 53.
• each of the machines M 1 , M2... Mn operates with the same application program 50 on each machine Ml, M2...Mn and thus all of the machines Ml, M2...Mn have the same application code and data 50.
• each of the machines Ml, M2...Mn operates with the same (or substantially the same) modifier 51 on each machine Ml, M2...Mn and thus all of the machines Ml, M2...Mn have the same (or substantially the same) modifier 51 with the modifier of machine M2 being designated 51/2.
• each application 50 has been modified by the corresponding modifier 51 according to the same rules (or substantially the same rules since minor optimising changes are permitted within each modifier 51/1 ...51/n).
• each of the machines Ml, M2...Mn has, say, a shared memory capability of 10MB, then the total shared memory available to each application 50 is not, as one might expect, lOn MB but rather only 10MB.
• each machine M 1 , M2... Mn has an unshared memory capability.
• the unshared memory capability of the machines Ml, M2...Mn are normally approximately equal but need not be.
• DRT 71 distributed run time
• the application 50 is loaded onto the Java Virtual Machine 72 via the distributed runtime system 71 through the loading procedure indicated by arrow 75.
• a distributed run time system is available from the Open Software Foundation under the name of Distributed Computing Environment (DCE).
• DCE Distributed Computing Environment
• the distributed runtime 71 comes into operation during the loading procedure indicated by arrow 75 of the JAVA application 50 so as to initially create the JAVA virtual machine 72. The sequence of operations during loading will be described hereafter in relation to Fig. 9.
• Fig. 8 shows in modified form the arrangement of Fig. 5 utilising JAVA virtual machines, each as illustrated in Fig. 7. It will be apparent that again the same application 50 is loaded onto each machine Ml, M2...Mn. However, the communications between each machine Ml, M2...Mn, and indicated by arrows 83, although physically routed through the machine hardware, are controlled by the individual DRT's 71/1...71/n within each machine. Thus, in practice this may be conceptionalised as the DRT's 71/1...71/n communicating with each other via the network 73 rather than the machines Ml, M2...Mn themselves. Turning now to Figs. 7 and 9, during the loading procedure 75, the program 50 being loaded to create each JAVA virtual machine 72 is modified.
• This modification commences at 90 in Fig. 9 and involves the initial step 91 of detecting all memory locations (termed fields in JAVA - but equivalent terms are used in other languages) in the application 50 being loaded. Such memory locations need to be identified for subsequent processing at steps 92 and 93.
• the DRT 71 during the loading procedure 75 creates a list of all the memory locations thus identified, the JAVA fields being listed by object and class. Both volatile and synchronous fields are listed.
• the next phase (designated 92 in Fig. 9) of the modification procedure is to search through the executable application code in order to locate every processing activity that manipulates or changes field values corresponding to the list generated at step 91 and thus writes to fields so the value at the corresponding memory location is changed.
• an "updating propagation routine" is inserted by step 93 at this place in the program to ensure that all other machines are notified that the value of the field has changed.
• the loading procedure continues in a normal way as indicated by step 94 in Fig. 9.
• An alternative form of initial modification during loading is illustrated in
• step 103 the start and listing steps 90 and 91 and the searching step 92 are the same as in Fig. 9.
• an "alert routine” is inserted at step 103.
• the “alert routine” instructs a thread or threads not used in processing and allocated to the DRT, to carry out the necessary propagation. This step 103 is a quicker alternative which results in lower overhead.
• a thread 121/2 has become aware of a change of field value at step 113, it instructs DRT processing 120 (as indicated by step 125 and arrow 127) that another thread(s) 121/1 allocated to the DRT processing 120 is to propagate in accordance with step 128 via the network 53 to all other machines M2...Mn the identity of the changed field and the changed value detected at step 113.
• This is an operation which can be carried out quickly and thus the processing of the initial thread 111/2 is only interrupted momentarily as indicated in step 125 before the thread 111/2 resumes processing in step 115.
• the other thread 121/1 which has been notified of the change (as indicated by arrow 127) then communicates that change as indicated in step 128 via the network 53 to each of the other machines M2...Mn.
• This second arrangement of Fig. 12 makes better utilisation of the processing power of the various threads 111/1...111/3 and 121/1 (which are not, in general, subject to equal demands) and gives better scaling with increasing size of "n", (n being an integer greater than or equal to 2 which represents the total number of machines which are connected to the network 53 and which run the application program 50 simultaneously). Irrespective of which arrangement is used, the changed field and identities and values detected at step 113 are propagated to all the other machines M2... Mn on the network.
• Fig. 13 This is illustrated in Fig. 13 where the DRT 71/1 and its thread 121/1 of Fig. 12 (represented by step 128 in Fig. 13) sends via the network 53 the identity and changed value of the listed memory location generated at step 113 of Fig. 12 by processing in machine Ml, to each of the other machines M2...Mn. Each of the other machines M2...Mn carries out the action indicated by steps
• the identities and values of changed fields can be grouped into batches so as to further reduce the demands on the communication speed of the network 53 interconnecting the various machines.
• each DRT 71 when initially recording the fields, for each field there is a name or identity which is common throughout the network and which the network recognises.
• the memory location corresponding to a given named field will vary over time since each machine will progressively store changed field values at different locations according to its own internal processes.
• the table in each of the DRTs will have, in general, different memory locations but each global "field name" will have the same "field value” stored in the different memory locations.
• a particular machine say machine M2
• loads the application code on itself modifies it, and then loads each of the other machines Ml,
• each of machines Ml, M3, ... Mn loads what it is given by machine M2.
• each machine receives the application code, but modifies it and loads the modified code on that machine. This enables the modification carried out by each machine to be slightly different being optimized based upon its architecture and operating system, yet still coherent with all other similar modifications.
• a particular machine say Ml, loads the unmodified code and all other machines M2, M3 ... Mn do a modification to delete the original application code and load the modified version.
• the supply can be branched (ie M2 supplies each of Ml, M3,
• the machines Ml to Mn can send all load requests to an additional machine (not illustrated) which is not running the application program, which performs the modification via any of the aforementioned methods, and returns the modified routine to each of the machines Ml to Mn which then load the modified routine locally.
• machines Ml to Mn forward all load requests to this additional machine which returns a modified routine to each machine.
• the modifications performed by this additional machine can include any of the modifications covered under the scope of the present invention. Persons skilled in the computing arts will be aware of at least four techniques used in creating modifications in computer code. The first is to make the modification in the original (source) language. The second is to convert the original code (in say JAVA) into an intermediate representation (or intermediate language). Once this conversion takes place the modification is made and then the conversion is reversed. This gives the desired result of modified JAVA code.
• the third possibility is to convert to machine code (either directly or via the abovementioned intermediate language). Then the machine code is modified before being loaded and executed.
• the fourth possibility is to convert the original code to an intermediate representation, which is then modified and subsequently converted into machine code.
• the present invention encompasses all four modification routes and also a combination of two, three or even all four, of such routes.
• a machine (produced by any one of various manufacturers and having an operating system operating in any one of various different languages) can operate in the particular language of the application program 50, in this instance the JAVA language. That is, a JAVA virtual machine 72 is able to operate code 50 in the JAVA language, and utilize the JAVA architecture irrespective of the machine manufacturer and the internal details of the machine. Furthermore, the single machine of Fig. 14 is able to easily perform synchronization of specific objects 50X-50Z when specified by the programmer's use of a synchronization routine. As each object exists only locally, the single JAVA virtual machine 72 of Fig.
• synchronization The process whereby only one object or class is exclusively used is termed "synchronization".
• the instructions “monitorenter” and “monitorexit” signify the beginning and ending of a synchronization routine which results in the acquiring of and releasing of a "lock” respectively which prevents an asset being the subject of contention.
• a plurality of individual computers or machines Ml, M2 Mn are provided each of which are interconnected via a communications network 53 and each of which is provided with a modifier 51 (as in Fig. 5 and realized by the DRT 71 in Fig. 8) and loaded with a common application program 50.
• the modifier 51 or DRT 71 ensures that when part of the application program 50 running on one of the machines exclusively utilizes (eg, by means of synchronization) a particular local asset, such as an objects 50X-50Z or class 50A, no other machine M2...Mn utilizes the corresponding asset in its local memory.
• the application program is scrutinized in order to detect program steps which define a synchronization routine. This scrutiny can take place either prior to loading, or during the loading procedure, or even after the loading procedure (but before execution of the relevant corresponding portion of the application code). It may be likened to a compilation procedure with the understanding that the term compilation normally involves a change in code or language, eg from source to object code or one language to another. However, in the present instance the term “compilation" (and its grammatical equivalents) is not so restricted and can also include embrace modifications within the same code or language.
• Annexure Dl is a typical code fragment from an unmodified synchronization routine
• Annexure D2 is an equivalent in respect of a modified synchronization routine
• Annexures Dl and D2 are the before and after excerpt of a synchronization routine respectively.
• the modified code that is added to the method is highlighted in bold.
• the code increments a shared memory location (counter) within in synchronize statement.
• the purpose of the synchronize statement is to ensure thread-safety of the increment operation in multithreaded applications.
• each machine would perform synchronization in isolation, thus potentially incrementing the shared counter at the same time, leading to potential race condition(s) and incoherent memory. Clearly this is not what the programmer of the application program expects to happen.
• the application code is modified as it is loaded into the machine by changing the synchronization routine.
• the changes made are the initial instructions and ending instructions that the synchronization routine executes.
• These added instructions act to additionally perform synchronization across all other machines in the distributed environment, thereby preserving the synchronize behaviour of the application program across a plurality of machines.
• the acquireLock() method of the DRT takes an argument which represents a unique identifier for this object (See Annexure D2), for example the name of the object, a reference to the object in question, or a unique number representing this object across all nodes, to be used in acquiring a global lock of the specified object.
• the DRT can support the synchronization of multiple objects at the same time without becoming confused as to which of the multiple objects are already synchronized and which are not, by using the unique identifier of each object to consult the correct record in the shared synchronization table.
• the DRT can determine the synchronization state of the object in a number of ways. Preferably, it can ask each machine in turn if their local copy of this object is presently synchronized, and if any machine replies true, then to wait until that object is unsynchronised, otherwise synchronize this object locally.
• the DRT on the local machine can consult a shared record table (perhaps on a separate machine (eg machine X), or a coherent shared record table on the local machine, or a database) to determine if this object has been marked as synchronized by any other machine, and if so, then wait until the status of the object is changed to "unsynchronised” and then acquire the lock by marking the object as synchronized, otherwise acquire the lock by marking the object as synchronized by this machine.
• a shared record table perhaps on a separate machine (eg machine X), or a coherent shared record table on the local machine, or a database
• the DRT determines that no other machine currently has a lock for this object (ie, no other machine has synchronized this object), then to acquire the lock for this object on all other machines, for example by means of modifiying the corresponding entry in a shared table of synchronization states, or alternatively, sequentially acquiring the lock on all other machines in addition the current machine. Only once this machine has successfully confirmed that no other machine has currently synchronized this object, and this machine has correspondingly synchronized locally, can the execution of the original synchronized code-block begin..
• this machine is to postpone execution of the original synchronize code-block until such a time as the DRT can confirm than no other machine is presently executing a synchronize statement for this object, and that this machine has correspondingly synchronized the object locally.
• the original code block is NOT to be executed until this machine can guarantee that no other machine is executing a synchronize statement for this object, as it will potentially corrupt the object across the participating machines due to race-conditions, inconsistency of memory, and so forth resulting from the concurrent execution of synchronized statements.
• the DRT determines that this object is presently "synchronized"
• the DRT prevents execution of the original code-block by pausing the execution of the "acquireLock()" operation until such a time as a corresponding "releaseLock()” operation is executed by the present owner of the lock.
• the machine which presently "owns” a lock indicates the close of its synchronized statement, for example by marking this object as “unsynchronised” in the shared table of synchronization states, or alternatively, sequentially releasing locks acquired on all other machines.
• any other machine waiting to begin execution of a corresponding synchronized statement can then claim ownership of this object's lock by resuming execution of its postponed (ie delayed) "acquireLock()" operation, for example, marking itself as executing a synchronized statement for this object in the shared table of synchronization states, or alternatively, sequentially acquiring local locks on each of the other machines.
• the application code is modified as it is loaded into the machine by changing the synchronization routine (consisting of a beginning "monitorenter” and an ending "monitorexit” instruction/s).
• the changes made are the initial instructions that the synchronization routine executes.
• These added instructions check if this lock has already been acquired by another machine. If this lock has not been acquired by another machine, then the DRT of this machine notifies all other machines that this machine has acquired the lock, and thereby stopping the other machines from executing synchronization routines for this lock.
• the DRT can record the lock status of the machines in many ways, for example:
• the DRT individually consults each machine to ascertain if this lock is already acquired. If so, the DRT pauses the execution of the synchronization routine until all other machines no longer own a lock on this asset or object. Otherwise, the DRT executes this synchronization routine.
• the DRT individually consults each machine to ascertain if this lock is already acquired. If so, the DRT pauses the execution of the synchronization routine until all other machines no longer own a lock on this asset or object. Otherwise, the DRT executes this synchronization routine.
• the DRT consults a shared table of records (for example a shared database, or a copy of a shared table on each of the participating machines) which indicate if any machine currently "owns" this lock. If so, the DRT then pauses execution of the synchronization routine on this machine until all other machines no longer own a lock on this object. Otherwise the DRT records this machine in the shared table (or tables, if there are multiple tables of records, eg, on multiple machines) as the owner of this lock, and then executes the synchronization routine .
• a shared table of records for example a shared database, or a copy of a shared table on each of the participating machines
• the DRT can "un-record" the lock status of machines in many alternative ways, for example: 1. corresponding to the exit to a synchronization routine, the DRT individually notifies each other machine that it no longer owns the lock. Alternatively, 2. corresponding to the exit to a synchronization routine, the DRT updates the record for this locked asset or object in the shared table(s) of records such that this machine is no longer recorded as owning this lock.
• the DRT can queue machines needing to acquire a locked object in multiple alternative ways, for example:
• the DRT notifies the present owner of the locked object that a specific machine would like to acquire the lock upon release by the current owning machine.
• the specified machine if there are no other waiting machines, then stores a record of the specified machine's interest in a table, which, following the exit of the synchronization routine of the locked object, then notifies the waiting machine that it can acquire this locked object, and thus begin executing its synchronization routine,
• the DRT notifies the present owner of the locked object that a specific machine (say machine M6) would like to acquire the lock upon release by that machine (say machine M4). That machine M4, if it finds after consulting its records of waiting machines for this locked object, finds that there are already one or more machines waiting, then either appends machine M6 to the end of the list of machines wanting to acquire this locked object, or alternatively, forwards the request from M6 to the first waiting, or any other machine waiting, machine which then, in turn, records machine M6 in their table of records,
• the DRT records itself in a shared table(s) of records (for example, a table stored in a shared database accessible by all machines, or multiple separate tables which are substantially similar). Still further, the DRT can notify other machines queued to acquire this lock corresponding to the exit of a synchronization routine by this machine in the following alternative ways, for example:
• the DRT notifies one of the awaiting machines (for example, this first machine in the queue of waiting machines) that the lock is released,
• the DRT notifies one of the awaiting machines (for example, the first machine in the queue of waiting machines) that the lock is released, and additionally, provides a copy of the entire queue of machines (for example, the second machine and subsequent machines awaiting for this lock).
• the second machine inherits the list of waiting machines from the first machine, and thereby ensures the continuity of the queue of waiting machines as each machine in turn down the list acquires and subsequently releases the lock.
• a modification to the general arrangement of Fig. 8 is provided in that machines Ml, M2...Mn are as before and run the same application program 50 (or programmes) on all machines simultaneously.
• a server machine X which is conveniently able to supply housekeeping functions, for example, and especially the synchronization of structures, assets and resources.
• Such a server machine X can be a low value commodity computer such as a PC since its computational load is low.
• two server machines X and X+l can be provided for redundancy purposes to increase the overall reliability of the system. Where two such server machines X and X+l are provided, they are preferably operated as dual machines in a cluster. It is not necessary to provide a server machine X as its computational load can be distributed over machines Ml, M2...Mn.
• a database operated by one machine in a master/slave type operation
• Fig. 16 shows a preferred general procedure to be followed. After loading 161 has been commenced, the instructions to be executed are considered in sequence and all synchronization routines are detected as indicated in step 162. In the JAVA language these are the "monitorenter” and “monitorexit” instructions. Other languages use different terms.
• a synchronization routine is detected, it is modified, typically by inserting further instructions into the routine. Alternatively, the modifying instructions could be inserted prior to the routine. Once the modification has been completed the loading procedure continues.
• the modifications preferably take the form of an "acquire lock on all other machines" operation and a "release lock on all other machines” modification as indicated at step 163.
• Fig. 17 illustrates a particular form of modification.
• the structures, assets or resources in JAVA termed classes or objects eg 50A, 50X-50Y
• This table also includes the synchronization status of the class or object. In the preferred embodiment, this table also includes a queue arrangement which stores the identities of machines which have requested use of this asset.
• step 173 of Fig. 17 next an "acquire lock" request is sent to machine X, after which, the sending machine awaits for confinnation of lock acquisition as shown in step 174.
• the global name is already locked (ie the corresponding asset is in use by another machine other than the machine proposing to acquire the lock) then this means that the proposed synchronization routine of the object or class should be paused until the object or class is unlocked by the current owner.
• the global name is not locked, this means that no other machine is using this class or object, and confirmation of lock acquisition is received straight away.
• execution of the synchronization routine is allowed to continue, as shown in step 175
• Fig. 18 shows the procedures followed by the application program executing machine which wishes to relinquish a lock.
• the initial step is indicated at step 181.
• the operation of this proposing machine is temporarily interrupted by steps 183, 184 until the reply is received from machine X, corresponding to step 184, and execution then resumes as indicated in step 185.
• the machine requesting release of a lock is made to lookup the "global name" for this lock preceding a request being made to machine X. This way, multiple locks on multiple machines can be acquired and released without interfering with one another.
• Fig. 19 shows the activity carried out by machine X in response to an "acquire lock" enquiry (of Fig. 17).
• the lock status is determined at steps 192 and 193 and, if no - the named resource is not free, the identity of the enquiring machine is added at step 194 to (or forms) the queue of awaiting acquisition requests.
• the answer is yes - the named resource is free- the corresponding reply is sent at step 197.
• the waiting enquiring machine is then able to execute the synchronization routine accordingly by carrying out step 175 of Fig. 17.
• the shared table is updated at step 196 so that the status of the globally named asset is changed to "locked".
• Fig. 20 shows the activity carried out by machine X in response to a "release lock" request of Fig. 18.
• machine X After receiving a "release lock” request at step 201, machine X optionally, and preferably, confirms that the machine requesting to release the lock is indeed the current owner of the lock", as indicated in step 202.
• the queue status is determined at step 203 and, if no-one is waiting to acquire this lock, machine X marks this lock as "unowned” in the shared table, as shown in step 207, and optionally sends a confirmation of release back to the requesting machine, as indicated by step 208. This enables the requesting machine to execute step 185 of Fig. 18.
• step 204 if yes - that is, other machines are waiting to acquire this lock - machine X marks this lock as now acquired by the next machine in the queue, as shown in step 204, and then sends a confirmation of lock acquisition to the queued machine at step 205, and consequently removes the new lock owner from the queue of waiting machines, as indicated in step 206.
• a particular machine say machine M2 loads the synchronization routine on itself, modifies it, and then loads each of the other machines Ml, M3 ... Mn (either sequentially or simultaneously) with the modified synchronization routine.
• machine M2 which may be termed "master/slave" each of machines Ml, M3, ... Mn loads what it is given by machine M2.
• machine M2 loads the synchronization routine in unmodified form on machine M2 and then on the other machines deletes the synchronization routine in its entirety and loads the modified code.
• the modification is not a by-passing of the synchronization routine but a deletion of it on all machines except one.
• each machine receives the synchronization routine, but modifies it and loads the modified routine on that machine. This enables the modification carried out by each machine to be slightly different being optimized based upon its architecture and operating system, yet still coherent with all other similar modifications.
• a particular machine say Ml, loads the unmodified synchronization routine and all other machines M2, M3 ... Mn do a modification to delete the original synchronization routine and load the modified version.
• the supply can be branched (ie M2 supplies each of Ml, M3, M4, etc directly) or cascaded or sequential (ie M2 applies Ml which then supplies M3 which then supplies M4, and so on).
• the machines Ml to Mn can send all load requests to an additional machine X (of Fig. 15), which performs the modification via any of the afore mentioned methods, and returns the modified routine to each of the machines Ml to Mn which then load the modified routine locally.
• machines Ml to Mn forward all load requests to machine X, which returns a modified routine to each machine.
• the modifications performed by machine X can include any of the modifications covered under the scope of the present invention.
• the first is to make the modification in the original (source) language.
• the second is to convert the original code (in say JAVA) into an intermediate representation (or intermediate language). Once this conversion takes place the modification is made and then the conversion is reversed. This gives the desired result of modified JAVA code.
• the third possibility is to convert to machine code (either directly or via the abovementioned intermediate language). Then the machine code is modified before being loaded and executed.
• the fourth possibility is to convert the original code to an intermediate representation, which is then modified and subsequently converted into machine code.
• the present invention encompasses all four modification routes and also a combination of two, three or even all four, of such routes.
• the computers 101 and 102 are not necessarily identical and indeed, one can be an IBM or IBM-clone and the other can be an APPLE computer.
• the computers 101 and 102 have two screens 105, 115 two keyboards 106, 116 but a single mouse 107.
• the two machines 101, 102 are interconnected by a means of a single coaxial cable or twisted pair cable 314.
• Two simple application programs are downloaded onto each of the machines 101, 102, the programs being modified as they are being loaded as described above.
• the first application is a simple calculator program and results in the image of a calculator 108 being displayed on the screen 105.
• the second program is a graphics program which displays four coloured blocks 109 which are of different colours and which move about at random within a rectangular box 310. Again, after loading, the box 310 is displayed on the screen 105.
• Each application operates independently so that the blocks 109 are in random motion on the screen 105 whilst numerals within the calculator 108 can be selected (with the mouse 107) together with a mathematical operator (such as addition or multiplication) so that the calculator 108 displays the result.
• the mouse 107 can be used to "grab" the box 310 and move same to the right across the screen 105 and onto the screen 115 so as to arrive at the situation illustrated in Fig. 22.
• the calculator application is being conducted on machine 101 whilst the graphics application resulting in display of box 310 is being conducted on machine 102.
• JAVA includes both the JAVA language and also JAVA platform and architecture.
• memory locations include, for example, both fields and array types.
• the above description deals with fields and the changes required for array types are essentially the same mutatis mutandis.
• the present invention is equally applicable to similar programming languages (including procedural, declarative and object orientated) to JAVA including Micrsoft.NET platform and architecture (Visual Basic, Visual CVC**, and C#) FORTRAN, C/C "1" , COBOL, BASIC etc.
• synchronization routine is to be understood to include within its scope both the JAVA synchronization routine and the "combination" of the JAVA synchronization routine and the LINUX or HOTSPOT code fragments which perform lock acquisition and release.
• object and class used herein are derived from the JAVA environment and are intended to embrace similar terms derived from different environments such as dynamically linked libraries (DLL), or object code packages, or function unit or memory locations.
• DLL dynamically linked libraries
• This first excerpt is part of the modification code. It searches through the code array, and when it finds a putstatic instruction (opcode 178), it implements the modifications.
• This third excerpt is part of the DRT Sending.
• This code fragment shows the DRT in a separate thread, after being notified, sending the value across the network.
• Field field modifiedClass . getDeclaredField ("myFieldl") ; // Stores // the field // from the // modified // class.
• the field is a byte field, while (DRT. isRunnin () ) ⁇ synchronized (ALERT_LOCK) ⁇ ALERT_LOCK.wait() ; // The DRT thread is waiting for the alert // method to be called.
• byteU b new byte [] ⁇ nameTag, field. getByte (null) ⁇ ; // Stores // the // nameTag // and the // value // of the // field from // the modified // class in a // buffer.
• DatagramPacket dp new DatagramPacket (b, 0, b. length); ms.send(dp); // Send the buffer out across the network.
• the fourth excerpt is part of the DRT receiving. This is a fragment of code to receive a DRT sent alert over the network.
• MulticastSocket ms DRT .getMulticastSocket ( ) ; // The multicast socket // used by the DRT for // communication.
• Field field modifiedClass .getDeclaredField( "myFieldl") ; // Stores the // field from // the modified // class.
• the field is a byte field, while (DRT.isRunning) ⁇ ms. receive (dp) ; // Receive the previously sent buffer from the network.
• the seventh excerpt is the source-code of the example application used in excerpt 5 and 6. import java.lang.*; public class example ⁇
• the eighth excerpt is the source-code of FieldAlert, which alerts the "distributed run-time" to propagate a changed value.
• */ public final static Hashtable alerts new Hashtable(); /** Object handle.
• */ public Object reference null;
• the ninth excerpt is the source-code of FieldSend, which propagates changes values alerted to it via FieldAlert.
• int globallD (int) (( (buffer [index++] & Oxff) « 24) I ( (buffer [index++] & Oxff) « 16) I ( (buffe [index++] & Oxff) « 8) I (buffer [index++] & Oxff)); // Now, need to resolve the object in question.
• Object reference globallDToObject .ge ( new Intege (globallD) ) ; // Next, get the array of fields for this object.
• Field [] fields reference. getClass (). getDeclaredFields () ; while (index ⁇ length) ⁇ // Decode the field id.
• int fieldID (int) (( (buffe [index++] & Oxff) « 24) ] ( (buffer [index++] & Oxff) « 16) I ( (buffer [index++] & Oxff) « 8) I (buffer [index++] & Oxff) ) ; // Determine value length based on corresponding field // type.
• CONSTANT_Fieldref_info fi (CONSTANT_Fieldref_info) cf .
• CONSTANT_Class_info ci (C0NSTANT_Class_info) cf .
• ca.code[z+3] new byte [3];
• ca.code[z+3] [0] (byte) 184;
• ca.code[z+3] [1] (byte) ((alertindex » 8) & Oxff);
• ca.code [z+3] [2] (byte) (alertindex & Oxff); // And lastly, increase the CODE_LENGTH and
• Convience class for representing attribute nfo structures within ClassFiles import java.lang.*; import java.io.*;
• Convience class for representing ClassFile structures import java.lang.*; import java.io.*; import java.util . *;
• the ClassFile follows verbatim from the JVM specification. */ public final class ClassFile ⁇ public int magic; public int minor_version; public int major_version; public int constant_pool_count; public cp_info[] constant_pool; public int access_flags; public int this_class; public int super_class; public int interfaces_count; public int [ ] interfaces; public int fields_count; public field_info[] fields; public int methods_count; public method_info [] methods; public int attributes_count; public attribute_info [] attributes; /** Constructor. Takes in a byte stream representation and transforms * each of the attributes in the ClassFile into objects to allow for * easier manipulation.
• Convience class for representing Code_attribute structures within ClassFiles import java.util.*; import java.lang.*; import j ava . io . * ;
• Convience class for representing CONS TANT_NameAndType Jnfo structures within ClassFiles import java.io.*; import java.lang.*;
• ClassFiles import java . lang . * ; import j ava . io . * ; /** String subtype of a constant pool entry.
• */ public final class CONSTANT_String_info extends cp_info ⁇ /** The index to the actual value of the string .
• Convience class for representing cp Jnfo structures within ClassFiles import java.lang.*; import java.io.*;
• Convience class for representing Deprecated_attribute structures within ClassFiles import java.lang.*; import java.io.*;
• Convience class for representing Exceptions_attribute structures within ClassFiles import java.lang.*; import java.io.*;
• Convience class for representing fieldjnfo structures within ClassFiles import java.lang.*; import java.io.*;
• Convience class for representing InnerClasses_attribute structures within ClassFiles import java.lang.*; import java.io.*;
• Convience class for representing methodjnfo structures within ClassFiles import java.lang.*; import java.io.*;
• Convience class for representing SourceFile_attribute structures within ClassFiles import java.lang.*; import java.io.*;
• Convience class for representing Synthetic_attribute structures within ClassFiles import java.lang.*; import java.io.*;
• Example method using synchronization This method serves to illustrate the use of synchronization to implement thread-safe modification of a shared memory location by potentially multiple threads. */ public void run ( ) ⁇
• Annexure D4 import java.lang.*; import java.util.*; import java.net.*; import java.io.*;
• Hashtable hashCodeToGloballD new Hashtable
• Annexure D5 import java.lang.*; import java.util.*; import java.net.*; import java.io.*;
• Serversocket serversocket new ServerSocket (serverPort) ; while ( ! Thread. interrupted () ) ⁇
• Socket socket serverSocket . accept () ;
• This excerpt is the source-code of LockLoader, which modifies an application as it is being loaded.
• ca.code[z+2] new byte [3];
• ca.code[z+2] [0] (byte) 184;
• ca.code[z+2] [1] (byte) ((exitindex » 8) & Oxff) ;
• ca.code[z+2] [2] (byte) (exitindex & Oxff) ; // And lastly, increase the CODE_LENGTH and

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