Abstract:
A method, apparatus, system, and signal-bearing medium that in an embodiment switch between blocking I/O and non-blocking I/O based on the number of concurrent connections. If the number of concurrent connections is greater than a high threshold, then blocking I/O is switched to non-blocking I/O. If the number of concurrent connections is less than a low threshold, then non-blocking I/O is switched to blocking I/O. In this way, I/O may be optimized depending on the number of concurrent connections, which increases performance.

Description:
FIELD  
       [0001]     An embodiment of the invention generally relates to computers. In particular, an embodiment of the invention generally relates to optimizing for both blocking and non-blocking input/output.  
       BACKGROUND  
       [0002]     The development of the EDVAC computer system of 1948 is often cited as the beginning of the computer era. Since that time, computer systems have evolved into extremely sophisticated devices, and computer systems may be found in many different settings. Computer systems typically include a combination of hardware (such as semiconductors, integrated circuits, programmable logic devices, programmable gate arrays, and circuit boards) and software, also known as computer programs.  
         [0003]     Years ago, computers were isolated devices that did not communicate with each other. But, today computers are often connected in networks, such as the Internet or World Wide Web, and a user at one computer, often called a client, may wish to access information at multiple other computers, often called servers, via a network. Accessing and using information from multiple computers is often called distributed computing.  
         [0004]     One of the challenges of distributed computing is handling input/output (I/O) transmissions across communications channels. A channel represents an open connection to an entity, such as a hardware device, a file, a network socket, or a program component that is capable of performing one or more distinct I/O operations, such as reading or writing data. Data transfers to communications channels can be implemented using either blocking or non-blocking I/O. In blocking I/O, also called synchronous I/O, each communications connection is assigned its own programming thread. A programming thread (a process or a part of a process) is a programming unit that is scheduled for execution on a processor and to which resources such as execution time, locks, and queues may be assigned. Blocking I/O typically has faster response times and works well for smaller numbers of concurrently open connections than does non-blocking I/O.  
         [0005]     In non-blocking I/O, also called asynchronous I/O, all communications connections share the same programming thread or the same set of threads. Non-blocking I/O does not perform as well as blocking I/O for small numbers of concurrent connections, but non-blocking I/O does have the advantage that it scales well to large numbers of concurrent connections because non-blocking I/O does not associate a thread with each concurrent connection. Instead, in non-blocking I/O, the available thread(s) are shared between the concurrent connections, which reduces overhead since each additional thread has an associated overhead. Thus, non-blocking I/O scales to much larger numbers of concurrent connections, but trades off response time to gain this scalability.  
         [0006]     Current techniques provide two implementations: both blocking I/O and non-blocking I/O, which require two APIs (application programming interfaces) and two programming models. This means duplicate code, one supporting blocking I/O and another providing non-blocking I/O support. It also means that middleware can only handle one type of load efficiently, either fewer concurrent connections with optimal response time or more concurrent channels trading off response time. This forces a system administrator to guess which load is likely to occur and to configure either blocking I/O or non-block I/O based on that guess, which may be incorrect, leading to poor performance.  
         [0007]     Without a better way to handle a variety of I/O loads, distributed computing will continue to have difficulty handling a variety of numbers of concurrent connections, leading to poor performance.  
       SUMMARY  
       [0008]     A method, apparatus, system, and signal-bearing medium are provided that in an embodiment switch between blocking I/O and non-blocking I/O based on the number of concurrent connections. If the number of concurrent connections is greater than a high threshold, then blocking I/O is switched to non-blocking I/O. If the number of concurrent connections is less than a low threshold, then non-blocking I/O is switched to blocking I/O. In this way, I/O may be optimized depending on the number of concurrent connections, which increases performance. 
     
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0009]      FIG. 1  depicts a block diagram of an example system for implementing an embodiment of the invention.  
         [0010]      FIG. 2  depicts a flowchart of example processing for handling a request for a new connection by an I/O (Input/Output) manager, according to an embodiment of the invention.  
         [0011]      FIG. 3  depicts a flowchart of example processing for handling a request to close a connection by the I/O manager, according to an embodiment of the invention.  
         [0012]      FIG. 4  depicts a flowchart of example processing for handling an I/O request by the I/O manager, according to an embodiment of the invention.  
     
    
     DETAILED DESCRIPTION  
       [0013]     Referring to the Drawing, wherein like numbers denote like parts throughout the several views,  FIG. 1  depicts a high-level block diagram representation of a computer system  100  connected to a client  132  via a network  130 , according to an embodiment of the present invention. The major components of the computer system  100  include one or more processors  101 , a main memory  102 , a terminal interface  111 , a storage interface  112 , an I/O (Input/Output) device interface  113 , and communications/network interfaces  114 , all of which are coupled for inter-component communication via a memory bus  103 , an I/O bus  104 , and an I/O bus interface unit  105 .  
         [0014]     The computer system  100  contains one or more general-purpose programmable central processing units (CPUs)  101 A,  101 B,  101 C, and  101 D, herein generically referred to as the processor  101 . In an embodiment, the computer system  100  contains multiple processors typical of a relatively large system; however, in another embodiment the computer system  100  may alternatively be a single CPU system. Each processor  101  executes instructions stored in the main memory  102  and may include one or more levels of on-board cache.  
         [0015]     The main memory  102  is a random-access semiconductor memory for storing data and programs. The main memory  102  is conceptually a single monolithic entity, but in other embodiments the main memory  102  is a more complex arrangement, such as a hierarchy of caches and other memory devices. For example, memory may exist in multiple levels of caches, and these caches may be further divided by function, so that one cache holds instructions while another holds non-instruction data, which is used by the processor or processors. Memory may further be distributed and associated with different CPUs or sets of CPUs, as is known in any of various so-called non-uniform memory access (NUMA) computer architectures.  
         [0016]     The memory  102  includes threads  144  and an I/O manager  150 . Although the threads  144  and the I/O manager  150  are illustrated as being contained within the memory  102  in the computer system  100 , in other embodiments some or all of them may be on different computer systems and may be accessed remotely, e.g., via the network  130 . The computer system  100  may use virtual addressing mechanisms that allow the programs of the computer system  100  to behave as if they only have access to a large, single storage entity instead of access to multiple, smaller storage entities. Thus, while the threads  144  and the I/O manager  150  are illustrated as residing in the memory  102 , these elements are not necessarily all completely contained in the same storage device at the same time.  
         [0017]     The I/O manager  150  receives and processes requests from the clients  132  to open and close connections and perform I/O requests, such as reads and writes of data to/from the clients  132 . The I/O manager  150  further allocates the connections and data transfer requests among the threads  144 , using either blocking I/O or non-blocking I/O. The threads  144  execute on the processor  101  to perform the data transfers. In an embodiment, the I/O manager  150  includes instructions capable of executing on the processor  101  or statements capable of being interpreted by instructions executing on the processor  101  to perform the functions as further described below with reference to  FIGS. 2, 3 , and  4 . In another embodiment, the I/O manager  150  may be implemented in microcode. In yet another embodiment, the I/O manager  150  may be implemented in hardware via logic gates and/or other appropriate hardware techniques, in lieu of or in addition to a processor-based system.  
         [0018]     The memory bus  103  provides a data communication path for transferring data among the processors  101 , the main memory  102 , and the I/O bus interface unit  105 . The I/O bus interface unit  105  is further coupled to the system I/O bus  104  for transferring data to and from the various I/O units. The I/O bus interface unit  105  communicates with multiple I/O interface units  111 ,  112 ,  113 , and  114 , which are also known as I/O processors (IOPs) or I/O adapters (IOAs), through the system I/O bus  104 . The system I/O bus  104  may be, e.g., an industry standard PCI (Peripheral Component Interconnect) bus, or any other appropriate bus technology. The I/O interface units support communication with a variety of storage and I/O devices. For example, the terminal interface unit  111  supports the attachment of one or more user terminals  121 ,  122 ,  123 , and  124 .  
         [0019]     The storage interface unit  112  supports the attachment of one or more direct access storage devices (DASD)  125 ,  126 , and  127  (which are typically rotating magnetic disk drive storage devices, although they could alternatively be other devices, including arrays of disk drives configured to appear as a single large storage device to a host). The contents of the DASD  125 ,  126 , and  127  may be loaded from and stored to the memory  102  as needed. The storage interface unit  112  may also support other types of devices, such as a tape device  131 , an optical device, or any other type of storage device.  
         [0020]     The I/O and other device interface  113  provides an interface to any of various other input/output devices or devices of other types. Two such devices, the printer  128  and the fax machine  129 , are shown in the exemplary embodiment of  FIG. 1 , but in other embodiment many other such devices may exist, which may be of differing types. The network interface  114  provides one or more communications paths from the computer system  100  to other digital devices and computer systems; such paths may include, e.g., one or more networks  130 .  
         [0021]     Although the memory bus  103  is shown in  FIG. 1  as a relatively simple, single bus structure providing a direct communication path among the processors  101 , the main memory  102 , and the I/O bus interface  105 , in fact the memory bus  103  may comprise multiple different buses or communication paths, which may be arranged in any of various forms, such as point-to-point links in hierarchical, star or web configurations, multiple hierarchical buses, parallel and redundant paths, etc. Furthermore, while the I/O bus interface  105  and the I/O bus  104  are shown as single respective units, the computer system  100  may in fact contain multiple I/O bus interface units  105  and/or multiple I/O buses  104 . While multiple I/O interface units are shown, which separate the system I/O bus  104  from various communications paths running to the various I/O devices, in other embodiments some or all of the I/O devices are connected directly to one or more system I/O buses.  
         [0022]     The computer system  100  depicted in  FIG. 1  has multiple attached terminals  121 ,  122 ,  123 , and  124 , such as might be typical of a multi-user “mainframe” computer system. Typically, in such a case the actual number of attached devices is greater than those shown in  FIG. 1 , although the present invention is not limited to systems of any particular size. The computer system  100  may alternatively be a single-user system, typically containing only a single user display and keyboard input, or might be a server or similar device which has little or no direct user interface, but receives requests from other computer systems (clients). In other embodiments, the computer system  100  may be implemented as a personal computer, portable computer, laptop or notebook computer, PDA (Personal Digital Assistant), tablet computer, pocket computer, telephone, pager, automobile, teleconferencing system, appliance, or any other appropriate type of electronic device.  
         [0023]     The network  130  may be any suitable network or combination of networks and may support any appropriate protocol suitable for communication of data and/or code to/from the computer system  100 . In various embodiments, the network  130  may represent a storage device or a combination of storage devices, either connected directly or indirectly to the computer system  100 . In an embodiment, the network  130  may support Infiniband. In another embodiment, the network  130  may support wireless communications. In another embodiment, the network  130  may support hard-wired communications, such as a telephone line or cable. In another embodiment, the network  130  may support the Ethernet IEEE (Institute of Electrical and Electronics Engineers) 802.3x specification. In another embodiment, the network  130  may be the Internet and may support IP (Internet Protocol). In another embodiment, the network  130  may be a local area network (LAN) or a wide area network (WAN). In another embodiment, the network  130  may be a hotspot service provider network. In another embodiment, the network  130  may be an intranet. In another embodiment, the network  130  may be a GPRS (General Packet Radio Service) network. In another embodiment, the network  130  may be a FRS (Family Radio Service) network. In another embodiment, the network  130  may be any appropriate cellular data network or cell-based radio network technology. In another embodiment, the network  130  may be an IEEE 802.11B wireless network. In still another embodiment, the network  130  may be any suitable network or combination of networks. Although one network  130  is shown, in other embodiments any number of networks (of the same or different types) may be present.  
         [0024]     The client  132  requests the I/O manager  150  to open and close connections to the computer system  100  and sends I/O requests to I/O manager  150 . The client  132  may include some or all of the hardware components previously described above for the computer system  100 . Although only one client  132  is illustrated, in other embodiments any number of clients may be present.  
         [0025]     It should be understood that  FIG. 1  is intended to depict the representative major components of the computer system  100  and the client  132  at a high level, that individual components may have greater complexity than represented in  FIG. 1 , that components other than or in addition to those shown in  FIG. 1  may be present, and that the number, type, and configuration of such components may vary. Several particular examples of such additional complexity or additional variations are disclosed herein; it being understood that these are by way of example only and are not necessarily the only such variations.  
         [0026]     The various software components illustrated in  FIG. 1  and implementing various embodiments of the invention may be implemented in a number of manners, including using various computer software applications, routines, components, programs, objects, modules, data structures, etc., referred to hereinafter as “computer programs,” or simply “programs.” The computer programs typically comprise one or more instructions that are resident at various times in various memory and storage devices in the computer system  100 , and that, when read and executed by one or more processors  101  in the computer system  100 , cause the computer system  100  to perform the steps necessary to execute steps or elements embodying the various aspects of an embodiment of the invention.  
         [0027]     Moreover, while embodiments of the invention have and hereinafter will be described in the context of fully functioning computer systems, the various embodiments of the invention are capable of being distributed as a program product in a variety of forms, and the invention applies equally regardless of the particular type of signal-bearing medium used to actually carry out the distribution. The programs defining the functions of this embodiment may be delivered to the computer system  100  via a variety of signal-bearing media, which include, but are not limited to: 
        (1) information permanently stored on a non-rewriteable storage medium, e.g., a read-only memory device attached to or within a computer system, such as a CD-ROM readable by a CD-ROM drive;     (2) alterable information stored on a rewriteable storage medium, e.g., a hard disk drive (e.g., DASD  125 ,  126 , or  127 ) or diskette; or     (3) information conveyed to the computer system  100  by a communications medium, such as through a computer or a telephone network, e.g., the network  130 , including wireless communications.        
 
         [0031]     Such signal-bearing media, when carrying machine-readable instructions that direct the functions of the present invention, represent embodiments of the present invention.  
         [0032]     In addition, various programs described hereinafter may be identified based upon the application for which they are implemented in a specific embodiment of the invention. But, any particular program nomenclature that follows is used merely for convenience, and thus embodiments of the invention should not be limited to use solely in any specific application identified and/or implied by such nomenclature.  
         [0033]     The exemplary environments illustrated in  FIG. 1  are not intended to limit the present invention. Indeed, other alternative hardware and/or software environments may be used without departing from the scope of the invention.  
         [0034]      FIG. 2  depicts a flowchart of example processing for handling a request for a new connection by the I/O (Input/Output) manager  150 , according to an embodiment of the invention. Control begins at block  200 . Control then continues to block  205  where the I/O manager  150  receives a request for a new connection from the client  132  for a protocol. In various embodiments, the protocol may be HTTP (Hypertext Transport Protocol), JMS (Java Message Service), SMTP (Simple Mail Transfer Protocol), or any other appropriate protocol. The I/O manager  150  processes the requests for new connections on a protocol-by-protocol basis.  
         [0035]     Control then continues to block  210  where the I/O manager  150  determines whether the number of concurrent connections for the protocol exceeds a high threshold. In various embodiments, each of the protocols may have the same high threshold, or some or all of the protocols may have different high thresholds. If the determination at block  210  is true, then the number of concurrent connections for the protocol exceeds the high threshold, so control continues to block  215  where the I/O manager  150  switches to non-blocking I/O for the protocol between the computer system  100  and the client  132  if non-blocking I/O is not already being used. Thus, the I/O manager  150  will transfer data on the connection using non-blocking I/O, meaning that concurrent connections for the protocol are processed by the same thread  144 .  
         [0036]     Control then continues to block  220  where the I/O manager  150  determines whether the number of concurrent connections is greater than the maximum number of connections for the protocol. In an embodiment, the maximum number of connections for the protocol is greater than the high threshold for the protocol. If the determination at block  220  is true, then the number of concurrent connections is greater than the maximum number of connections for the protocol, so control continues from block  220  to block  225  where the I/O manager  150  selects an active connection that has the minimum disruption for I/O operations between the computer system  100  and the clients  132 , i.e., a connection that can be closed safely because it&#39;s at an appropriate point (called a window) in the protocol that allows it to be safely closed without interrupting I/O operations. Many protocols have such windows, such as HTTP and IIOP (Internet Inter-object Request Broker Protocol). Control then continues to block  230  where the I/O manager  150  closes the selected connection. Control then continues to block  299  where the logic of  FIG. 2  returns.  
         [0037]     If the determination at block  220  is false, then the number of concurrent connections is not greater than the maximum number of connections for the protocol, so control continues from block  220  to block  299  where the logic of  FIG. 2  returns.  
         [0038]     If the determination at block  210  is false, then the number of concurrent connections for the protocol does not exceed the high threshold for the protocol, so control continues from block  210  to block  299  where the logic of  FIG. 2  returns.  
         [0039]      FIG. 3  depicts a flowchart of example processing for handling a request from the client  132  to close a connection by the I/O manager  150 , according to an embodiment of the invention. Control begins at block  300 . Control then continues to block  305  where the I/O manager  150  receives a request from the client  132  to close a connection.  
         [0040]     Control then continues to block  310  where the I/O manager  150  determines whether the number of concurrent connections for the protocol is less than a low threshold. In an embodiment, the low threshold for the protocol is less than the high threshold for the protocol, and each protocol may have the same or a different low threshold. If the determination at block  310  is true, then the number of concurrent connections for the protocol is less than the low threshold, so control continues from block  310  to block  315  where the I/O manager  150  switches from non-blocking I/O to blocking I/O between the computer system  100  and the client  132  if the I/O manager  150  was previously using non-blocking I/O for the protocol. Blocking I/O means that concurrent connections for the protocol are processed by different of the threads  144 . Control then continues to block  399  where the logic of  FIG. 3  returns.  
         [0041]     If the determination at block  310  is false, then the number of concurrent connections for the protocol is not less than the low threshold, so control continues from block  310  to block  399  where the logic of  FIG. 3  returns.  
         [0042]      FIG. 4  depicts a flowchart of example processing for handling an I/O request by the I/O manager  150 , according to an embodiment of the invention. Control begins at block  400 . Control then continues to block  405  where the I/O manager  150  receives an I/O request for a thread from the client  132 . Control then continues to block  410  where the I/O manager  150  increments a count of I/O requests for the thread. Control then continues to block  415  where the I/O manager  150  determines whether the count of I/O requests is greater than a threshold. If the determination at block  415  is true, then the count of I/O requests is greater than the threshold, so control continues to block  420  where the I/O manager  150  starts a new thread for the connection and processes the request using the new thread. Control then continues to block  499  where the logic of  FIG. 4  returns.  
         [0043]     If the determination at block  415  is false, then the count of the I/O requests is not greater than the threshold, so control continues from block  415  to block  425  where the I/O manager  150  processes the received request in the current thread. Control then continues to block  499  where the logic of  FIG. 4  returns.  
         [0044]     In the previous detailed description of exemplary embodiments of the invention, reference was made to the accompanying drawings (where like numbers represent like elements), which form a part hereof, and in which is shown by way of illustration specific exemplary embodiments in which the invention may be practiced. These embodiments were described in sufficient detail to enable those skilled in the art to practice the invention, but other embodiments may be utilized and logical, mechanical, electrical, and other changes may be made without departing from the scope of the present invention. Different instances of the word “embodiment” as used within this specification do not necessarily refer to the same embodiment, but they may. The previous detailed description is, therefore, not to be taken in a limiting sense, and the scope of the present invention is defined only by the appended claims.  
         [0045]     In the previous description, numerous specific details were set forth to provide a thorough understanding of embodiments of the invention. But, embodiments of the invention may be practiced without these specific details. In other instances, well-known circuits, structures, and techniques have not been shown in detail in order not to obscure the invention.