Abstract:
A method and apparatus is provided for providing and integrating high-performance message queues. “Contexts” are provided that allow independent worlds to be created and execute in parallel. A context is created with one or more threads. Each object is created with context affinity, allowing any thread inside the context to modify the object or process pending messages. Threads in a different context are unable to modify the object or process pending messages for that context. To help achieve scalability and context affinity, both global and thread-local data is often moved into the context. Remaining global data has independent locks, providing synchronized access for multiple contexts. Each context has multiple message queues to create a priority queue. There are default queues for sent messages and posted messages, carry-overs from legacy window managers, with the ability to add new queues on demand. A queue bridge is also provided for actually processing the messages.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application claims the benefit of U.S. provisional patent application No. 06/244,481, filed Oct. 30, 2000, which is expressly incorporated herein by reference. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention generally relates to the field of computing devices with graphical user interfaces. More specifically, this invention relates to providing high-performance message queues and integrating such queues with message queues provided by legacy user interface window managers.  
         BACKGROUND OF THE INVENTION  
         [0003]    Graphical user interfaces typically employ some form of a window manager to organize and render windows. Window managers commonly utilize a window tree to organize windows, their child windows, and other objects to be displayed within the window such as buttons, menus, etc. To display the windows on a display screen, a window manager parses the window tree and renders the windows and other user interface objects in memory. The memory is then displayed on a video screen. A window manager may also be responsible for “hit-testing” input to identify the window in which window input was made. For instance, when a user moves a mouse cursor over a window and “clicks,” the window manager must determine the window in which the click was made and generate a message to that window.  
           [0004]    In some operating systems, such as Windows® NT from the Microsoft® Corporation of Redmond, Wash., there is a single window manager that threads in all executing processes call into. Because window manager objects are highly interconnected, data synchronization is achieved by taking a system-wide “lock”. Once inside this lock, a thread can quickly modify objects, traverse the window tree, or any other operations without requiring additional locks. As a consequence, this allows only a single thread into the messaging subsystem at a time. This architecture provides several advantages in that many operations require access to many components and also provides a greatly simplified programming model that eliminates most deadlock situations that would arise when using multiple window manager objects.  
           [0005]    Unfortunately, a system-wide lock seriously hampers the communications infrastructure between user interface components on different threads by allowing only a single message to be en-queued or de-queued at a time. Furthermore, such an architecture imposes a heavy performance penalty on component groups that are independent of each other and could otherwise run in parallel on independent threads.  
           [0006]    One solution to these problems is to change from a system-wide (or process-wide) lock to individual object locks that permits only objects affected by a single operation to be synchronized. This solution actually carries a heavier performance penalty, however, because of the number of locks introduced, especially in a world with control composition. Such a solution also greatly complicates the programming model.  
           [0007]    Another solution involves placing a lock on each user interface hierarchy, potentially stored in the root node of the window tree. This gives better granularity than a single, process-wide lock, but imposes many restrictions when performing cross tree operations between inter-related trees. This also does not solve the synchronization problem for non-window user interface components that do not exist in a tree.  
           [0008]    Therefore, in light of the above, there is a need for a method and apparatus for providing high-performance message queues in a user interface environment that does not utilize a system-wide lock but that minimizes the number of locked queues. There is a further need for a method and apparatus for providing high-performance message queues in a user interface environment that can integrate a high-performance non-locking queue with a queue provided by a legacy window manager.  
         SUMMARY OF THE INVENTION  
         [0009]    The present invention solves the above-problems by providing a method and apparatus for providing and integrating high-performance message queues in a user interface environment. Generally described, the present invention provides high-performance message queues in a user interface environment that can scale when more processors are added. This infrastructure provides the ability for user interface components to run independently of each other in separate “contexts.” In practice, this allows communication between different components at a rate of 10-100 times the number of messages per second than possible in previous solutions.  
           [0010]    More specifically described, the present invention provides contexts that allow independent “worlds” to be created and execute in parallel. A context is created with one or more threads. Each object is created with context affinity, which allows only threads associated with the context to modify the object or process pending messages. Threads associated with another context are unable to modify the object or process pending messages for that context.  
           [0011]    To help achieve scalability and context affinity, both global and thread-local data may be moved into the context. Remaining global data has independent locks that provide synchronized access for multiple contexts. Each context also has multiple message queues that together create a priority queue. There are default queues for “sent” messages and “posted” messages, carry-overs from legacy window managers, and new queues may be added on demand. A queue bridge is also provided for actually processing the messages that may be integrated with a legacy window manager.  
           [0012]    The present invention also provides a method, computer-controlled apparatus, and a computer-readable medium for providing and integrating high-performance message queues in a user interface environment. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, wherein:  
         [0014]    [0014]FIG. 1 is a block diagram showing an illustrative operating environment for an actual embodiment of the present invention.  
         [0015]    [0015]FIG. 2 is a block diagram showing aspects of an operating system utilized in conjunction with the present invention.  
         [0016]    [0016]FIG. 3 is a block diagram illustrating additional aspects of an operating system utilized in conjunction with the present invention.  
         [0017]    [0017]FIG. 4 is a block diagram showing an illustrative software architecture for aspects of the present invention.  
         [0018]    [0018]FIG. 5 is a block diagram showing an illustrative software architecture for additional aspects of the present invention.  
         [0019]    [0019]FIG. 6 is a flow diagram showing an illustrative routine for transmitting a message between user interface objects according to an actual embodiment of the present invention.  
         [0020]    [0020]FIG. 7 is a flow diagram showing an illustrative routine for transmitting a message from one user interface component to another user interface component in another context according to an actual embodiment of the present invention.  
         [0021]    [0021]FIG. 8 is a flow diagram showing an illustrative routine for atomically adding an object into an s-list according to an actual embodiment of the present invention.  
         [0022]    [0022]FIG. 9 is a flow diagram showing an illustrative routine for posting a message according to an actual embodiment of the present invention.  
         [0023]    [0023]FIG. 10 is a flow diagram showing an illustrative routine for processing a message queue according to an actual embodiment of the present invention  
         [0024]    [0024]FIG. 11 is a flow diagram showing additional aspects an illustrative routine for processing a message queue according to an actual embodiment of the present invention.  
         [0025]    [0025]FIG. 12 is a flow diagram showing an illustrative routine for processing an s-list according to an actual embodiment of the present invention.  
         [0026]    [0026]FIG. 13 is a flow diagram showing the operation of a queue bridge for integrating a high-performance message queue with a legacy message queue according to an embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0027]    The present invention is directed to a method and apparatus for providing high-performance message queues and for integrating these queues with message queues provided by legacy window managers. Aspects of the invention may be embodied in a computer executing an operating system capable of providing a graphical user interface.  
         [0028]    As will be described in greater detail below, the present invention provides a reusable, thread-safe message queue that provides “First in, All Out” behavior, allowing individual messages to be en-queued by multiple threads. By creating multiple instances of these low-level queues, a higher-level priority queue can be built for all window manager messages. According to one actual embodiment of the present invention, a low-level queue is provided that does not have synchronization and is designed to be used by a single thread. According to another actual embodiment of the present invention, a low-level queue is provided that has synchronization and is designed to be safely accessed by multiple threads. Because both types of queues expose common application programming interfaces (“APIs”), the single threaded queue can be viewed as an optimized case of the synchronized queue.  
         [0029]    As also will be described in greater detail below, the thread-safe, synchronized queue, is built around “S-Lists.” S-Lists are atomically-created singly linked lists. S-Lists allow multiple threads to en-queue messages into a common queue without taking any “critical section” locks. By not using critical sections or spin-locks, more threads can communicate using shared queues than in previous solutions because the atomic changes to the S-List do not require other threads to sleep on a shared resource. Moreover, because the present invention utilizes atomic operations available in hardware, a node may be safely added to an S-List on a symmetric multi-processing (“SMP”) system in constant-order time. De-queuing is also performed atomically. In this manner, the entire list may be extracted and made available to other threads. The other threads may continue adding messages to be processed.  
         [0030]    Referring now to the figures, in which like numerals represent like elements, an actual embodiment of the present invention will be described. Turning now to FIG. 1, an illustrative personal computer  20  for implementing aspects of the present invention will be described. The personal computer  20  comprises a conventional personal computer, including a processing unit  21 , a system memory  22 , and a system bus  23  that couples the system memory to the processing unit  21 . The system memory  22  includes a read only memory (“ROM”)  24  and a random access memory (“RAM”)  25 . A basic input/output system  26  (“BIOS”) containing the basic routines that help to transfer information between elements within the personal computer  20 , such as during start-up, is stored in ROM  24 . The personal computer  20  further includes a hard disk drive  27 , a magnetic disk drive  28 , e.g., to read from or write to a removable disk  29 , and an optical disk drive  30 , e.g., for reading a CD-ROM disk  31  or to read from or write to other optical media such as a Digital Versatile Disk (“DVD”).  
         [0031]    The hard disk drive  27 , magnetic disk drive  28 , and optical disk drive  30  are connected to the system bus  23  by a hard disk drive interface  32 , a magnetic disk drive interface  33 , and an optical drive interface  34 , respectively. The drives and their associated computer-readable media provide nonvolatile storage for the personal computer  20 . As described herein, computer-readable media may comprise any available media that can be accessed by the personal computer  20 . By way of example, and not limitation, computer-readable media may comprise computer storage media and communication media. Computer storage media includes volatile and nonvolatile, removable and non-removable media implemented in any method or technology for storage of information such as computer readable instructions, data structures, program modules or other data. Computer storage media includes, but is not limited to, RAM, ROM, EPROM, EEPROM, flash memory or other solid-state memory technology, CD-ROM, DVD or other optical storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to store the desired information and which can be accessed by the personal computer  20 .  
         [0032]    A number of program modules may be stored in the drives and RAM  25 , including an operating system  35 , such as Windows®98, Windows® 2000, or Windows® NT from Microsoft® Corporation. As will be described in greater detail below, aspects of the present invention are implemented within the operating system  35  in the actual embodiment of the present invention described herein.  
         [0033]    A user may enter commands and information into the personal computer  20  through input devices such as a keyboard  40  or a mouse  42 . Other input devices (not shown) may include a microphone, touchpad, joystick, game pad, satellite dish, scanner, or the like. These and other input devices are often connected to the processing unit  21  through a serial port interface  46  that is coupled to the system bus  23 , but may be connected by other interfaces, such as a game port or a universal serial bus (“USB”). A monitor  47  or other type of display device is also connected to the system bus  23  via a display interface, such as a video adapter  48 . In addition to the monitor, the personal computer  20  may include other peripheral output devices, such as speakers  45  connected through an audio adapter  44  or a printer (not shown).  
         [0034]    As described briefly above, the personal computer  20  may operate in a networked environment using logical connections to one or more remote computers through the Internet  58 . The personal computer  20  may connect to the Internet  58  through a network interface  55 . Alternatively, the personal computer  20  may include a modem  54  and use an Internet Service Provider (“ISP”)  56  to establish communications with the Internet  58 . The modem  54 , which may be internal or external, is connected to the system bus  23  via the serial port interface  46 . It will be appreciated that the network connections shown are illustrative and other means of establishing a communications link between the personal computer  20  and the Internet  58  may be used.  
         [0035]    Referring now to FIG. 2, additional aspects of the operating system  35  will be described. The operating system  35  comprises a number of components for executing applications  72  and for communicating with the hardware that comprises the personal computer  20 . At the lowest level, the operating system  35  comprises device drivers  60  for communicating with the hardware of the personal computer  20 . The operating system  35  also comprises a virtual machine manager  62 , an installable file system manager  64 , and a configuration manager  66 . Each of these managers may store information regarding the state of the operating system  35  and the hardware of the personal computer  20  in a registry  74 . The operating system  35  also provides a shell  70 , which includes user interface tools. An operating system core  68  is also provided which supplies low-level functionality and hardware interfaces. According to the embodiment of the present invention described herein, aspects of the present invention are implemented in the operating system core  68 . The operating system core  68  is described in greater detail below with respect to FIG. 3.  
         [0036]    Turning now to FIG. 3, an illustrative operating system core  68  will be described. As mentioned above, the Windows® operating system from the Microsoft® Corporation provides an illustrative operating environment for the actual embodiment of the present invention described herein. The operating system core  68  of the Windows® operating system comprises three main components: the kernel  70 ; the graphical device interface (“GDI”)  72 ; and the User component  74 . The GDI  72  is a graphical system that draws graphic primitives, manipulates bitmaps, and interacts with device-independent graphics drivers, including those for display and printer output devices. The kernel  70  provides base operating system functionality, including file I/O services, virtual memory management, and task scheduling. When a user wants to start an application, the kernel  70  loads the executable (“EXE”) and dynamically linked library (“DLL”) files for the application. The kernel  70  also provides exception handling, allocates virtual memory, resolves import references, and supports demand paging for the application. As an application runs, the kernel  70  schedules and runs threads of each process owned by an application.  
         [0037]    The User component  74  manages input from a keyboard, mouse, and other input devices and output to the user interface (windows, icons, menus, and so on). The User component  74  also manages interaction with the sound driver, timer, and communications ports. The User component  74  uses an asynchronous input model for all input to the system and applications. As the various input devices generate interrupts, an interrupt handler converts the interrupts to messages and sends the messages to a raw input thread area, which, in turn, passes each message to the appropriate message queue. Each Win32-based thread may have its own message queue.  
         [0038]    In order to manage the output to the user interface, the User component  74  maintains a window manager  76 . The window manager  76  comprises an executable software component for keeping track of visible windows and other user interface objects, and rendering these objects into video memory. Aspects of the present invention may be implemented as a part of the window manager  74 . Also, although the invention is described as implemented within the Windows® operating system, those skilled in the art should appreciate that the present invention may be advantageously implemented within any operating system that utilizes a windowing graphical user interface.  
         [0039]    Referring now to FIG. 4, additional aspects of the present invention will be described. As shown in FIG. 4, the present invention provides a new system component for providing message queues  88 A- 88 N to threads  90 A- 90 N executing within an application  80 . According to an embodiment of the invention, the new system component provides separate contexts  84 A- 84 N. Each message queue  88 A- 88 N is associated with a corresponding context  84 A- 84 N. Any thread  90 A- 90 N in a given context  84 A- 84 N can process messages in the context&#39;s message queue. Threads  90 A- 90 N can send messages to other threads by utilizing their respecting message queues  88 A- 88 N. Contexts  84 A- 84 N also maintain locks  86 A- 86 N. As will be described in greater detail below, threads  90 A- 90 N within a particular context can send messages to other threads  90 A- 90 N within the same context without utilizing the message queue  88 A- 88 N. Moreover, the message queues  88 A- 88 N associated with each context  84 A- 84 N are implemented as non-locking using “atomic” hardware instructions known to those skilled in the art. Aspects of the present invention for sending messages, posting messages, and processing messages will be described below with respect to FIGS.  6 - 12 .  
         [0040]    Referring now to FIG. 5, additional aspects of the present invention will be described. As mentioned briefly above, in addition to providing high-performance message queues, the present invention also provides a method and apparatus for interfacing such queues with legacy window managers. According to the actual embodiment of the invention described herein, a queue bridge  94  is provided between a new window manager  84  having non-locking queues  88 A-N and a legacy window manager  76 , such as the window manager provided in the User component of Windows NT®.  
         [0041]    The queue bridge  94  satisfies all of the requirements of the User component message queue  92 , including: on legacy systems, only GetMessage(), MsgWaitForMultipleObjectsEx() and WaitMsg() can block the thread until a queue has an available message; once ready, only GetMessage() or PeekMessage() can be used to remove one message; legacy User component queues for Microsoft Windows®95 or Microsoft Windows® NT/4 require all messages to be processed between calls of MsgWaitForMultipleObjectsEx(); only the queue on the thread that created the HWND can receive messages for that window; the application must be able to use either ANSI or UNICODE versions of APIs to ensure proper data processing; and all messages must be processed in FIFO nature, for a given mini-queue.  
         [0042]    Later versions of Microsoft Windows® have been modified to expose message pump hooks (“MPH”) which allow a program to modify system API implementations. As known to those skilled in the art, a message pump  85  is a program loop that receives messages from a thread&#39;s message queue, translates them, offers them to the dialog manager, informs the Multiple Document Interface (“MDI”) about them, and dispatches them to the application.  
         [0043]    The queue bridge  94  also satisfies the requirements of the window manager having non-locking queues  82 , such as: operations on the queues must not require any locks, other than interlocked operations; any thread inside the context that owns a Visual Gadget may process messages for that Visual Gadget; and multiple threads may try to process messages for a context simultaneously, but all messages must be processed in FIFO nature, for a given queue.  
         [0044]    The queue bridge  94  also provides functionality for extensible idle time processing  83 , including animation processing, such as: objects must be able to update while the user interface is waiting for new messages to process; the user interface must be able to perform multiple animations on different objects simultaneously in one or more threads; new animations may be built and started while the queues are already waiting for new messages; animations must not be blocked waiting for a new message to become available to exit the wait cycle; and the overhead of integrating these continuous animations with the queues must not incur a significant CPU performance penalty. The operation of the queue bridge  94  will be described in greater detail below with reference to FIG. 13.  
         [0045]    Referring now to FIG. 6, an illustrative Routine  600  will be described for sending a Visual Gadget event, or message. The Routine  600  begins at block  602 , where the message request is received. Routine  600  continues from block  602  to block  604 , where parameters received with the message request are validated. From block  604 , the Routine  600  continues to block  605 , where the context associated with the current thread is determined. The Routine  600  then continues to block  606 , where a determination is made as to whether the context of the current thread is the same as the context of the thread for which the message is destined. If the contexts are the same, the Routine  600  branches to block  608 , where the queues are bypassed and the message is transmitted from the current thread directly to the destination thread. Sending a message to a component that has the same context (see below) is the highest priority message and can be done bypassing all queues. From block  608 , the Routine  600  continues to block  611 , where it ends.  
         [0046]    If, at block  606 , it is determined that the source and destination contexts are not the same, the Routine  600  continues from block  606  to block  610 , where the SendNL process is called. As will be described in detail below with respect to FIG. 7, the SendNL process sends a message to a non-locking queue in another context. From block  610 , the Routine  600  continues to block  611 , where it ends.  
         [0047]    Turning now to FIG. 7, a Routine  700  will be described that illustrates the SendNL process for sending a message to a component that has a different context Sending a message to a component that has a different context requires the message to be en-queued onto the receiving context&#39;s “sent” message queue, with the sending thread blocking until the message has been processed. Once the message has been processed, the message information must be recopied back, since the message processing may fill in “out” arguments for return values. “Sending” a message is higher-level functionality built on top of the message queue.  
         [0048]    The Routine  700  begins at block  702 , where the parameters received with the message are validated. The Routine  702  then continues to block  704 , where a processing function to handle when the message is “de-queued” is identified. The Routine  700  then continues to block  706  where memory is allocated for the message entry and the message entry is filled with the passed parameters. The Routine  700  then continues to block  708 , where an event handle signaling that the message has been processed is added to the message entry. Similarly, at block  710 , an event handle for processing outside messages received while the message is being processed is added to the message entry. At block  712 , the AddMessageEntry routine is called with the message entry. The AddMessageEntry routine atomically adds the message entry to the appropriate message queue and is described below with respect to FIG. 8.  
         [0049]    Routine  700  continues from block  712  to block  713 , where the receiving context is marked as having data. This process is performed “atomically.” As known to those skilled in the art, hardware instructions can be used to exchange the contents of memory without requiring a critical section lock. For instance, the “CMPXCHG8B” instruction of the Intel 80×86 line of processors accomplishes such a function. Those skilled in the art should appreciate that similar instructions are also available on other hardware platforms.  
         [0050]    From block  713 , the Routine  700  continues to block  714 , where a determination is made as to whether the message has been processed. If the message has not been processed, the Routine  700  branches to block  716 , where the thread waits for a return object and processes outside messages if any become available. From block  716 , the Routine  700  returns to block  714  where an additional determination is made as to whether the message has been processed. If, at block  714 , it is determined that the message has been processed, the Routine  700  continues to block  718 . At block  718 , the processed message information is copied back into the original message request. At block  720 , any allocated memory is de-allocated. The Routine  700  then returns at block  722 .  
         [0051]    Referring now to FIG. 8, an illustrative Routine  800  will be described for adding a message entry to a queue. The Routine  800  begins at block  802 , where the object is locked so that it cannot be fully destroyed. The Routine  800  then continues to block  804 , where the object is atomically added onto the queue. As briefly described above, according to an embodiment of the invention, the queue is implemented as an S-list. An S-list is a singly-linked list that can add a node, pop a node, or remove all nodes atomically. From block  804 , the Routine  800  continues to block  806 , where it returns.  
         [0052]    Referring now to FIG. 9, an illustrative Routine  900  will be described for “posting” a message to a queue. Messages posted to a component in any context must be deferred until the next time the application requests processing of messages. Because a specific thread may exit after posting a message, the memory may not be able to be returned to that thread. In this situation, memory is allocated off the process heap, allowing the receiving thread to safely free the memory.  
         [0053]    The Routine  900  begins at block  902 , where the parameters received with the post message request are validated. The Routine  900  then continues to block  904 , where the processing function that should be notified when the message is “de-queued” is identified. At block  906 , memory is allocated for the message entry and the message entry is filled with the appropriate parameters. The Routine  900  then continues to block  908 , where the AddMessageEntry routine is called. The AddMessageEntry routine is described above with reference to FIG. 8. From block  908 , the Routine  900  continues to block  910 , where the receiving context is atomically marked as having data. The Routine  900  then continues to block  912 , where it ends.  
         [0054]    Referring now to FIG. 10, an illustrative Routine  1000  will be described for processing a message queue. As mentioned briefly above, only one thread is allowed to process messages at a given time. This is necessary to ensure that all messages are processed in a first-in first-out (“FIFO”) order. When a thread is ready to process messages for a given message queue, because of the limitations of S-Lists, all messages must be de-queued. After the list is de-queued, the singly-linked list must be converted from a stack into a queue, giving the messages first-in, first-out (“FIFO”) ordering. At this point, all entries in the queue may be processed.  
         [0055]    The Routine  1000  begins at block  1002 , where a determination is atomically made as to whether any other thread is currently processing messages. If another thread is processing, the Routine  1000  branches to block  1012 . If no other thread is processing, the Routine  1002  continues to block  1004 , where an indication is atomically made that the current thread is processing the message queue. From block  1004 , the Routine  1000  continues to block  1006 , where a routine for atomically processing the sent message queue is called. Such a routine is described below with respect to FIG. 11.  
         [0056]    From block  1006 , the Routine  1000  continues to block  1008 , where routine for atomically processing the post message queue is called. Such a routine is described below with respect to FIG. 11. The Routine  1000  then continues to block  1010  where an indication is made that no thread is currently processing the message queue. The Routine  1000  then ends at block  1012 .  
         [0057]    Referring now to FIG. 11, an illustrative Routine  1100  will be described for processing the send and post message queues. The Routine  1100  begins at block  1102 , where a determination is made as to whether the S-list is empty. If the S-list is empty, the Routine  1100  branches to block  1110 , where it returns. If the S-list is not empty, the Routine  1100  continues to block  1104 , where the contents of the S-list are extracted atomically. The Routine  1100  then continues to block  1106 , where the list is reversed, to convert the list from a stack into a queue. The Routine  1100  then moves to block  1108 , where the ProcessList routine is called. The ProcessList routine is described below with reference to FIG. 12.  
         [0058]    Turning now to FIG. 12, an illustrative Routine  1200  for implementing the ProcessList routine will be described. The Routine  1200  begins at block  1202 , where a determination is made as to whether the S-list is empty. If the S-list is empty, the Routine  1200  branches to block  1216 , where it returns. If the S-list is not empty, the Routine  1200  continues to block  1204 , where the head message entry is extracted from the list. At block  1206 , the message entry is processed. From block  1206 , the Routine  1200  continues to block  1208 , where the context lock is taken. From block  1208 , the Routine  1200  continues to block  1210 , where the object is unlocked. At block  1212 , the context lock is released. At block  1214 , an S-list “add” is atomically performed to return memory to the sender. The Routine  1200  then continues to block  1216 , where it returns.  
         [0059]    Turning now to FIG. 13, an illustrative Routine  1300  will be described for providing a queue bridge between a window manager utilizing high-performance message queues and a legacy window manager. The Routine  1300  begins at block  1302 , where a determination is made as to whether a message has been received from the high-performance window manager. If a message has been received, the Routine  1300  branches to block  1310 , where all of the messages in the high-performance message manager queue are extracted and processed. This maintains the constraints required by non-locking queues. As described above, to ensure strict FIFO behavior, only one thread at a time within a context may process messages. The Routine  1300  then returns from block  1310  to block  1302 .  
         [0060]    If, at block  1302 , it is determined that no high-performance window manager messages are ready, the Routine  1300  continues to block  1304 . At block  1304 , a determination is made as to whether messages are ready to be processed from the legacy window manager. If no messages are ready to be processed, the Routine  1300  continues to block  1306 , where idle-time processing is performed. In this manner, background components are given an opportunity to update. Additionally, the wait time until the background components will have additional work may be computed.  
         [0061]    If, at block  1304 , it is determined that messages are ready to be processed from the legacy window manager, the Routine  1300  branches to block  1306 , where the next available message is processed. At decision block  1307 , a test is performed to determine whether the operating system has indicated that a message is ready. If the operating system has not indicated that a message is ready, the Routine  1300  returns to block  1306 . If the operating system has indicated that a message is ready, the Routine  1300  returns to block  1302 . This maintains existing queue behavior with legacy applications. The Routine  1300  then continues from block  1308  to block  1302  where additional messages are processed in a similar manner. Block  1308  saves the state and returns to the caller to process the legacy message.  
         [0062]    In light of the above, it should be appreciated by those skilled in the art that the present invention provides a method, apparatus, and computer-readable medium for providing high-performance message queues. It should also be appreciated that the present invention provides a method, apparatus, and computer-readable medium for integrating a high-performance message queue with a legacy message queue. While an actual embodiment of the invention has been illustrated and described, it will be appreciated that various changes can be made therein without departing from the spirit and scope of the invention.