Abstract:
A system for managing threads to handle transaction requests connected to input/output (I/O) subsystems to enable notification to threads to complete operations.

Description:
1. FIELD OF THE INVENTION  
       [0001]     Embodiments of the invention relate to a system for managing threads.  
       2. GENERAL BACKGROUND  
       [0002]     In computing systems, such as web servers or application servers, threads are used to handle transaction requests. A “thread” is generally defined as a sequence of instructions that, when executed, perform a task. Multiple threads may be processed concurrently to perform different tasks such as those tasks necessary to collectively handle a transaction request. A “transaction request” is a message transmitted over a network that indicates what kind of service is requested. For instance, the message may request to browse some data contained in a database. In order to service the request, the recipient initiates a particular task that corresponds to the nature of the requested task.  
         [0003]     One problem associated with conventional computing systems is that a significant amount of processing time is spent by a central processing unit (CPU) on thread management. In general, “thread management” involves management of queues, synchronizing, waking up and putting-to-sleep threads, context switches and many other known functions. For instance, in systems with a very high thread count, on the order of thousands for example, operations of the systems can be bogged down simply due to thread management and overhead, namely the time it takes to process threads.  
         [0004]     A proposed solution of reducing the high processing demands is to preclude the use of a large number of threads to handle transaction requests. Rather, single threads or a few threads may be configured to handle such requests. This leads to poor system scalability.  
         [0005]     Currently, there are computing systems that have threading control built into the CPU such as a CRAY® MTA™ computer. However, these systems suffer from a number of disadvantages. First, only a maximum of 128 threads are supported per CPU. As a result, support of a larger thread count would need to be implemented in software. Second, integrating circuitry to support up to 128 threads occupies a significant amount of silicon real estate, and thereby, increases the overall costs for the CPU. Third, the threading control hardware of conventional computing systems is stand-alone and is not connected to the rest of the system (e.g., input/output “I/O” circuitry). Since this hardware does not have the proper interface with the rest of the system, true automatic thread management is not provided (e.g., waking up a thread when a “file read” operation that the thread has been waiting on is completed).  
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0006]     The invention may best be understood by referring to the following description and accompanying drawings that are used to illustrate embodiments of the invention.  
         [0007]      FIG. 1  is a first exemplary diagram of a computing system featuring a thread control processor (TCP);  
         [0008]      FIG. 2  is a second exemplary diagram of a computing system featuring the TCP; and  
         [0009]      FIG. 3  is an exemplary block diagram illustrating operations of the TCP.  
     
    
     DETAILED DESCRIPTION  
       [0010]     Certain embodiments of the invention relate to a computing system, co-processor and method for managing threads. For one embodiment of the invention, thread management overhead is off-loaded to specialized hardware implemented in circuitry proximate to a system processor. In another embodiment of the invention, thread management is integrated into the system processor.  
         [0011]     Certain details are set forth below in order to provide a thorough understanding of various embodiments of the invention, albeit the invention may be practiced through many embodiments other that those illustrated. Well-known circuitry and operations are not set forth in detail in order to avoid unnecessarily obscuring this description.  
         [0012]     Herein, a “computing system” may generally be considered as hardware, software, firmware or any combination thereof that is configured to process transaction requests. Some illustrative examples of a computing system include a server (e.g., web server or application server), a set-top box and the like.  
         [0013]     A “thread” is a sequence instructions that, when executed, perform one or more functions or tasks. The threads may be stored in a processor-readable medium, which is any medium that can store or transfer information. Examples of “processor-readable medium” include, but are not limited or restricted to a programmable electronic circuit, a semiconductor memory device, a volatile memory (e.g., random access memory, etc.), a non-volatile memory (e.g., read-only memory, flash memory, etc.), a floppy diskette, an optical disk such as a compact disk (CD) or digital versatile disc (DVD), a hard drive disk, or any type of communication link.  
         [0014]     Referring to  FIG. 1 , an exemplary diagram of a computing system  100  is shown. The computing system  100  comprises a processor unit  110 , a thread control processor (TCP)  120 , a system memory  130 , synchronization primitives  140  and one or more I/O subsystems  150 .  
         [0015]     As shown in this embodiment of the invention, processor unit  110  comprises one or more (M) processors  112   1 - 112   M . The particular number “M” of processors forming processor unit  110  is optimized on the basis cost versus performance. For simplicity in the present description, two processors  112   1  and  112   M  are illustrated. An operating system (O/S)  114  is accessible to processors  112   1  and  112   M  and uses a driver  116  to communicate with TCP  120 .  
         [0016]     Each “processor” represents a central processing unit (CPU) of any type of architecture, such as complex instruction set computers (CISC), reduced instruction set computers (RISC), very long instruction word (VLIW), or hybrid architecture. Of course, a processor may be implemented as an application specific integrated circuit (ASIC), a digital signal processor, a state machine, or the like.  
         [0017]     As shown in  FIG. 1 , processor unit  110  is in communication with TCP  120 . TCP  120  may be implemented as (i) a co-processor (as shown) separately positioned on a circuit board featuring processor unit  110  or (ii) additional circuitry implemented either on the same integrated circuit chip of a processor (e.g., processor  112   1 ) or on a separate integrated circuit chip within the same processor package (see  FIG. 2 ).  
         [0018]     TCP  120  is responsible for maintaining threads (e.g., JAVA® threads) operating within the computing system  100 . For instance, TCP  120  performs wake-up and put-to-sleep, thread scheduling, event notification and other miscellaneous tasks such as queue management, priority computation and other like functions. Interconnects  160  and  170  are provided from the TCP  120  to synchronization primitives  140  and I/O subsystems  150 , respectively.  
         [0019]     For this embodiment of the invention, I/O subsystems  150  comprise networking network interface controllers (NICs)  152  and disk controllers  154 . These I/O devices may be configured to communicate with TCP  120 .  
         [0020]     Herein, embodied in hardware or software, synchronization primitives  140  include a mutual exclusion object (Mutex)  142  and/or a Semaphore  144 . Both of these primitives are responsible for coordinating the usage of shared resources such as files stored in system memory  130  or operating system (OS) routines.  
         [0021]     In general, Mutex  142  is a program object created to enable the sharing of the same resource by multiple threads. Typically, when a multi-threaded program is commenced, it creates a mutex for each selected resource. Thereafter, when a thread accesses a resource, a corresponding mutex is configured to indicate that the resource is unavailable. Once the thread has concluded its use of the resource, the mutex is unlocked to allow another thread access to the resource.  
         [0022]     Similar in purpose to Mutex  142 , Semaphore  144  is a variable with a value that indicates the status of a shared operating system (OS) resource. Hence, Semaphore  144  is normally located in designated place in operating system (or kernel) storage.  
         [0023]     Referring now to  FIG. 3 , an exemplary block diagram illustrating operations of the TCP  120  is shown. The TCP  120  manages all active threads in the computing system  100 . For simplicity in illustration, eight (8) threads  200 ,  210 ,  220 ,  230 ,  240 ,  250 ,  260  and  270  (generally referred to as “thread(s)  280 ”) are illustrated.  
         [0024]     In practice, however, thousands of threads may be utilized. The threads may be in either a RUN state, a WAIT state or a SLEEP state. For instance, threads existing in a RUN state and loaded in processor unit  110  include threads  200  and  210 .  
         [0025]     Other threads may be existing in a WAIT state such as threads  220  and  230  waiting on an I/O event within any of the I/O subsystems  150 . Hence, the TCP  120  supports automatic event notification, which allows signals to notify the TCP  120  about I/O events such as completion of a file read operation, completion of transmission of a message over a network via NIC and the like.  
         [0026]     Also, threads  240 ,  250  and  260  may also exist in a WAIT state by waiting on synchronization primitives such as Mutex  142   1 , Mutex  142   2  and/or Semaphore  144   1 . Alternatively, a thread such as thread  270  may simply be in a SLEEP state.  
         [0027]     As indicated upon, any thread  280  is placed in a RUN state when one of a number of conditions is satisfied. For instance, a thread  280  is ready-to-run when an I/O event that the thread is waiting on is completed. Alternatively, a thread  280  is ready-to-run when a synchronization primitive  140  that the thread  280  is waiting on is triggered. Yet another example is that a thread  280  is ready-to-run when it is awoken from a SLEEP state. The TCP  120  selects threads in a RUN state (i.e., ready-to-run threads) and provides them to one of the available processor  112   1 - 112   M  in the processor unit  110  for execution.  
         [0028]     In case of multiple threads in a RUN state being available, a priority-based scheduler (not shown) can be used to select one of the threads based on the chosen priority rules. Other scheduling algorithms such as the well-known round-robin technique can be used. Threads are placed into a SLEEP state when either time quanta expires or threads request an I/O operation from an I/O device.  
         [0029]     In general, TCP  120  can support multiple threading models. For example, JAVA® Threads or native operating system threads operate in accordance with embodiments of the invention. However, JAVA® threads are one preferred target for the TCP  120  because of their widespread use in current systems.  
         [0030]     In an embodiment where the TCP  120  is a separate co-processor, the TCP  120  may reside on a circuit board. Lower cost is enabled since the separate processor can use older technology and support a high number of threads. Thus, for the embodiment of  FIG. 1 , thread management hardware can be coupled directly to each of the I/O subsystems  150  and enable automatic event notification to threads such as completion of a file read operation. In contrast, traditional threading control hardware deals with threading control only.  
         [0031]     While the invention has been described in terms of various embodiments, the invention should not limited to only those embodiments described, but can be practiced with modification and alteration within the spirit and scope of the appended claims. The description is thus to be regarded as illustrative instead of limiting.