Patent Publication Number: US-7917601-B1

Title: Agent-based event-driven web server architecture

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. application Ser. No. 11/888,005, filed Jul. 31, 2007, which is a continuation of U.S. application Ser. No. 09/974,292, filed Oct. 9, 2001, which claims the benefit under 35 U.S.C. §119(e) of U.S. Provisional Patent Application No. 60/239,544, filed Oct. 10, 2000, and U.S. Provisional Patent Application No. 60/308,234, filed on Jul. 26, 2001. These applications are herein incorporated by reference in their entireties. 
    
    
     TECHNICAL FIELD 
     The present invention relates generally to data transmission on computer networks, and more particularly to networking devices and methods that employ an agent-based and/or event-driven web server software architecture. 
     BACKGROUND OF THE INVENTION 
     The Internet has experienced explosive growth in recent years. The emergence of the World Wide Web has enabled millions of users around the world to download easily web pages containing text, graphics, video, and sound data while at home, work, or from remote locations via wireless devices. These web pages often are large in size and therefore require a long time to download, causing the user delay and frustration. Delay often causes users to abandon the requested web page and move on to another web page, resulting in lost revenue and exposure for many commercial web sites. 
     Delay downloading a web page can be caused by a number of factors. For example, at the server, a large volume of page requests may overload the capacity of the server and result in unanswered or late-answered requests. One specific factor in delay at the server is caused by the server program inefficiently reading and writing data to and from network sockets. Another factor in delay is that management of a large number of connections by a web server can slow down the server, because the connections must be polled to determine whether any activity has occurred on the connections. This consumes valuable processor time, slowing down the rate at which the server may respond to requests. A third factor in delay is that server socket queues may become congested with requests that are computationally intensive, such as downloading a large image, thus slowing down smaller requests queued up behind these computationally intensive requests. 
     These factors and many others combine to delay current web server response time, frustrating users with long wait times for downloading web pages. Thus, a need exists for systems, methods, and devices that decrease web server delay, to create a more pleasurable web browsing experience. 
     SUMMARY OF THE INVENTION 
     A networking device, method, and software architecture are provided. The device may include a web server application program configured to run on an operating system of the device, and an event-based signaling mechanism configured to signal the web server application program when data has arrived on a socket of the operating system, by triggering an operating system-level signaling event. The web server application program is configured to read data off of the socket in response to detecting the event, without polling the socket first to determine that data is ready to be read from the socket. 
     The method may include receiving data from a client at a client socket on a networking device and creating an operating system-level event in response to receiving the data. The method may further include detecting the event from a component of a web server application program executed on the networking device, and in response, reading data off of the socket with the web server application program, without polling the socket to determine whether data is ready to read on the socket. The method may also include sending the data to a target web server, and in response to the sent data, receiving data from the target server at the networking device. The method may also include forwarding the data received from the target server, from the networking device to the client. 
     According to another aspect of the invention, the method may include receiving data from a network at a networking device, temporarily storing the data on a socket of the networking device, detecting the data stored on the socket using an operating system-level software component, and alerting an application-level process that data is ready to be read on the socket by creating an operating system-level signaling event. The method may further include detecting the event at the application level, and in response, reading the data from the socket via the application-level process. 
     The software architecture may include an operating system configured to read data from a network and temporarily store the data in a socket for access by an application program. The architecture may further include an operating system-level filter configured to detect when data has reached the socket from the network, and in response, trigger an operating system-level event to instruct an application program to read data from the socket. Typically the socket is not polled by the application program to determine whether data is ready to be read on the socket. 
     According to another aspect of the invention, the networking device may include a web server application program configured to run on an operating system having sockets for communicating with a network, and an operating system-level event-based means for signaling the arrival of data on the socket to the web server application program. The device may further include multiplexing agent means for associating a client session with one or more server sessions managed by the web server application program. 
     According to another aspect of the invention, the device may include a proxy web server positioned intermediate a client and a target web server on a network, and a plurality of multiplexing agents managed by the web server. The agents are typically configured to multiplex data from a number of client sessions to a smaller number of target server sessions. 
     According to another aspect of the invention, the device may include a proxy web server positioned intermediate a client and a target web server on a network, and means for multiplexing data from a number of client sessions to a smaller number of server sessions managed by the web server. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of a networking system according to one embodiment of the present invention. 
         FIG. 2  is a schematic view of a networking device of the networking system of  FIG. 1 . 
         FIG. 3  is a schematic view of a software architecture of the networking device of  FIG. 2 . 
         FIG. 4  is a schematic view of the networking system of  FIG. 1 , showing a plurality of multiplexing agents linking a number of client session state machines to a smaller number of server session state machines. 
         FIG. 5  is a schematic view of the networking system of  FIG. 1 , showing a single multiplexing agent communicating with a plurality of server session state machines. 
         FIG. 6  is a flowchart of a method according to one embodiment of the present invention. 
         FIG. 7  is a schematic view of a prior art server. 
         FIG. 8  is a diagram of a prior art input/output methods. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring initially to  FIGS. 7-8 , a prior art computing device is shown generally at  5 . Prior art computing device  5  typically includes a server program  5   a  and an operating system kernel  5   b . Server program  5   a  is configured to read and write data to and from an external computer network using input/output routines in the kernel  5   b . As data passes from the network into computing device  5 , it travels through a network interface, Internet Protocol (IP) input queue, and TCP/IP processing routines, to eventually arrive at a socket  5   c . Server program  5   a  executes a server process with the responsibility of reading data from socket  5   c.    
     Prior computing device  5  may be configured to read data off the socket using blocking I/O, nonblocking I/O, multiplexed I/O, or signal based I/O, as illustrated in  FIG. 7 . In blocking I/O, a server process  5   d  typically sends a command (e.g. RECVD) to read the socket, and waits for data to be ready on the socket. The process is blocked until the data is completely read from the socket. Prior web servers that use blocking I/O suffer from the problem that the server processes are blocked for lengthy time periods while waiting for data to appear on the sockets. Blocked processes consume valuable processor resources, and, in aggregate, slow the overall operation of the web server. 
     In nonblocking I/O, the server process repeatedly checks the socket to determine if data is ready, using, e.g., the EWOULDBLOCK command. The process sends a command to read the data (e.g. RECVD) only once it is determined that data is ready on the socket. Thus, the process is not continuously blocked while waiting for data to become ready on the socket. While an improvement over blocking I/O in terms of performance, the server process is blocked during the repeated checks to the socket to determine if data is ready. Prior web servers that use nonblocking I/O must manage these repeated checks for thousands of sockets at once, causing problematic delay under heavy loads. 
     In multiplexed I/O, the server process uses a command such as SELECT or POLL Unix commands to monitor a server socket to determine if data is ready to be read. The monitoring process is blocked while waiting for data to become ready on the socket, and again blocked when data is read from the socket. SELECT and POLL are not adequate for multiplexing I/O in a real world web server, because the web server would need to devote considerable processor time in order to monitor a large number of sockets at once, thereby resulting in delay and poor server performance under high load. 
     Regarding signal I/O, the author of perhaps the most widely used textbook on network programming has stated that “signal-driven I/O is next to useless with a TCP socket.” See, W. Richard Stevens, Unix Network Programming Volume 1, 22.2 (p. 590) (1998 2 nd  Edition), the entire disclosure of which is herein incorporated by reference. The reason for this is that according to prior approaches the signal is generated by a large number of events on the socket, and does not always indicate that data is ready on the socket. In the Unix operating environment, for example, the signal I/O can be attempted using the SIGIO command. However, the signal is generated whenever a connection request has been completed on a listening socket, a disconnect request has been initiated, a disconnect request has been completed, half of a connection has been shut down, data has arrived on a socket, data has been sent to a socket, or an asynchronous error occurred. (Stevens, 591) Thus, the server process will spend considerable processor time responding to “false alarms” when data is not actually ready for reading on the socket. 
     None of these prior approaches adequately address the need of the modern web server under heavy load to respond quickly to requests from thousands of simultaneously requesting clients. Instead, each causes the web server to consume valuable processor time while waiting for data to be made available on the socket, or, in the case of the prior signal I/O approach, while responding to signals that turn out to be “false alarms.” 
     Turning now to  FIG. 1 , a networking system according to one embodiment of the present invention is shown generally at  10 . Networking system  10  typically includes a plurality of clients  12  configured to exchange data with target web servers  14 , via a networking device  18 . Typically, clients  12  are configured to connect to networking device  18  via a Wide Area Network (WAN)  16  such as the Internet, and networking device  18  is configured to connect to target servers  14  via a Local Area Network (LAN)  20 . Alternatively, other suitable computer networks may be used in place of WAN  16  and LAN  20 . Networking device  18  is typically an acceleration device that acts as a proxy for the target server  14 , and is configured to increase the speed of the exchange of data between clients  12  and target servers  14 , as discussed below. 
     Typically, clients  12  are computing devices such as personal computers, portable computing devices, personal data assistants (PDAs), web-enabled wireless telephones, etc., and are configured to run a web browser  22  and to download web resources using the Hypertext Transfer Protocol (HTTP) and/or TCP/IP protocols from target web servers  14 . Exemplary web resources include static HyperText Markup Language (HTML) files, dynamically generated HTML data, image data, video data, sound data, graphics data, executable code such as applets written in Javascript, common gateway interface modules, and virtually any other data downloadable at a Uniform Resource Indicator (URI) using the HTTP protocol, and interpretable by a web browser. Exemplary web browser programs  22  include the Netscape browser commercially available from Netscape Communications Corporation of Santa Clara, Calif. and the Internet Explorer browser commercially available from Microsoft Corporation of Redmond, Wash. 
     As shown in  FIG. 2 , clients  12  typically include a processor  24  configured to communicate with volatile memory  26 , such as RAM, and non-volatile memory  28 , such as Flash Memory, ROM, a hard drive, etc., via a bus  30 , in order to execute a web server application program  32  and an operating system  34  stored in non-volatile memory  28 . Typically, the operating system is a Unix compatible operating system, such as the BSD operating system developed at the University of California at Berkeley. Typically, the operating system includes a kernel, that is, a central module of the operating system responsible for process, task, and memory management. Although the term kernel is common to the Unix compatible operating systems, it will be understood that the present invention may be implemented using other operating systems, such as Microsoft WINDOWS and MacOS. Thus, any use of the term kernel should be understood not to be limited to the Unix environment, but as referring generally to that portion of any operating system that is responsible for process, task, and memory management. Typically the kernel is continuously resident in volatile memory  26  while the networking device is in operation. 
     Networking device  18  also typically includes a network interface  36  configured to enable the device to send and receive data, such as web resources, to and from WAN  16  and LAN  20 . The data typically travels in packets according to the TCP/IP protocols. It will be understood that networking device  18  may be connected to a plurality of servers  14  in a one to many relationship, as shown in  FIG. 1 , or to only one server  14  in a one to one relationship. Networking device  18  may alternatively be installed as an integrated networking device  18 ′, which typically includes software and/or hardware components that are installed within a server  14 ′. 
     In addition to the features described above, networking devices  18 ,  18 ′ also may have features described with relation to the networking devices and acceleration devices disclosed in co-pending U.S. patent application Ser. Nos. 09/680,675, 09/680,997, and 09/680,998, filed Oct. 6, 2000, Nos. 60/239,552 and 60/239,071, filed Oct. 10, 2000, No. 60/287,188, filed Apr. 27, 2002, No. 09/882,375 filed Jun. 15, 2001, and No. 60/308,234 filed Jul. 26, 2001, and No. 60/313,006 filed Aug. 16, 2001, the disclosures of each of which are herein incorporated by reference. 
       FIG. 3  shows a software architecture of networking device  18 . Networking device  18  is typically configured to execute an operating system  34  having a kernel. As discussed above, the operating system is typically a Unix compatible operating system such as BSD, although WINDOWS, MacOS, or virtually any other suitable operating system may be used. Networking device  18  is also typically configured to execute a web server application program  32 . Because the web server application program  32  is typically positioned intermediate clients  12  and target servers  14 , and serves data directly to clients  12  in the place of target servers  14 , program  32  may be referred to as a “proxy” web server application program. 
     The operating system kernel is typically referred to as being at operating system level or kernel level, while application program  32  is typically referred to as being at application level or user process level. Management and scheduling routines in kernel  34  control which user processes have access to processor time for execution. 
     Typically, data from client  12  comes to networking device  18  through WAN  16  and enters a network input/output (I/O) routines  40  for processing. Network I/O routines  40  typically include a network interface  42  configured to initially receive data from the network, a IP input queue  44  configured to temporarily store data received from the network interface, TCP/IP processing routines  46  for managing TCP/IP connections, and a socket  48  for making the data available to application programs on networking device  18 . Typically, data passes through the network interface  42  to be stored in IP input queue  44  until TCP/IP routines  46  are free to read the data from the IP input queue  44  and process the data. Once TCP/IP routines have processed the data, removing IP headers, etc., the data passes to a socket  48 . A socket  48  that is associated with a particular client  12  may be referred to as a client socket. 
     Networking device  18  also typically includes an event-based signaling mechanism  52  configured to signal the web server application program  32  when data has arrived on a socket  48  of the operating system  34 . The signaling mechanism  52  typically includes a filter  54 , and a queue  56  of signaling events  58 . Typically, filter  54  is configured to detect the arrival of data on the socket from the network, and in response, create a signaling event  58  in the queue  56  to signal to web server application  32  that data is ready for reading on the socket. Typically, the filter is not configured to cause signaling events to enter the queue under any other circumstances, thus ensuring that data is ready for reading on the socket when a signaling event is written into the queue. This reduces false alarms that occurred in prior art signaling methods, discussed above. 
     Typically the queue is a KQUEUE, and the events are KEVENTS, which are routines available for the 4.3 BSD operating system. Filter  54 , event  58 , and queue  56  are all operation system level components, and thus typically are given high priority by scheduling routines within operating system  34 . 
     The web server application program  32  is typically configured to detect the entry of signaling event  58  into queue  56 . Thus, the web server application program is configured to read data off of the socket in response to detecting signaling event  58 , without polling the socket first to determine that data is ready to be read from the socket. Typically, accept state machine  62 , described below, is the component of the web server application program  32  that is configured to detect event  58  in queue  56 , although other components may alternatively be assigned this functionality. 
     Web server application program  32  typically is a configured as a proxy server, such that the web server application program receives requests from a client, sends the requests to a target server, receives responses from the target server, and forwards the responses to the requesting clients. Web server application program  32  typically includes a state machine subsystem  60  configured to accomplish these tasks. As used herein, the term state machine defines a program consisting of a set of states, and one or more transition functions which map input to from a current state to a next state. This is a very simple, but powerful, computational model, and its use in the present invention allows the web server application program to process data very quickly, consuming a minimum amount of processor time. 
     State machine subsystem  60  typically includes a first accept state machine  62  configured to detect event  58  created in queue  56  by the event-based signaling mechanism  52 , and, in response, read data off of the socket  48  associated with the requesting client. State machine subsystem  60  also includes a forward state machine  66  configured to write data to the socket  48  associated with the requesting client. Typically, data written to the socket  48  will be related to a response from target server  14 . 
     State machine subsystem  60  also includes a client session state machine  64  configured to manage network communications with the requesting client, via socket  48  associated with the client. Typically, this is accomplished by utilizing the first accept state machine  62  and the forward state machine  66  to read and write data to socket  48 , as needed. 
     State machine subsystem  60  further includes a multiplexing agent  68  configured to control the flow of data between client session state machine  64  and one or more server session state machines  70 , as described in more detail below with reference to  FIGS. 4-5 . Server session state machine  70  typically is configured to manage network communications with the target server, via the socket associated with the target server  48   a . This is typically accomplished by utilizing a second accept machine  74  and a target state machine  72 . The target state machine  72  is configured to write data to a socket  48   a  associated with a target server  14 , and the second accept state machine  74  is configured to read data from a socket  48   a  associated with the target server. Socket  48   a  may alternatively be referred to as a target server socket. While only one target server socket is shown in  FIG. 3 , it should be appreciated that a single client typically connects to a server  14  through more than one server socket and more than one server session state machine, depending on congestion, as described in co-pending U.S. patent application Ser. No. 09/882,375 filed Jun. 15, 2001, the disclosure of which is herein incorporated by reference, and as described below with reference to  FIGS. 4-5 . 
     Similar to the first accept state machine, the second accept machine is configured to detect an event  58   a  created by a second event signaling mechanism  52   a , and, in response, read data of off the socket  48   a  associated with the target server. The second event signaling mechanism  52   a  includes a filter  54   a  and event queue  56   a  similar to those described above, and functions similar to signaling mechanism  52 , and will not be redescribed in detail for the sake of brevity. 
     As shown in  FIG. 4 , networking device  18  typically includes a plurality of multiplexing agents, the agents being configured to multiplex a number of client sessions handled by client session state machines  64  to a smaller number of server sessions handled by server session state machines  70 . Typically, each multiplexing agent is configured to be associated with a single client session state machine, and is configured to be associated with a plurality of server session state machines, as shown in  FIG. 5 . Thus, data for a first request from a client  12   a  may pass through a client session  64   a  through a multiplexing agent  68   a , and along path  71  to a first server session, while data for a second request from the same client may pass through a client session  64   a , through a multiplexing agent  68   a , and along path  73  to a second server session  70   b . This enables the multiplexing agents to route requests to a least busy server socket, in order to optimize the response time of server  14 . Alternatively, the multiplexing agent may be associated with more than one client session state machine, and/or only a single server session state machine. 
     In addition to performance advantages gained by routing requests to the least busy server socket, multiplexing the client sessions down to a smaller number of server sessions enables faster response time from server  14  because the server  14  is freed from managing a large number of simultaneous connections. Managing a large number of connections typically slows down a web server, because the server is constantly polling open connections to determine whether there is any activity on the connection. 
     Turning now to  FIG. 6 , a method according to one embodiment of the present invention is shown generally at  100 . Networking device  18 , described above, is typically configured to implement method  100 , and the other method embodiments described herein. Typically, method  100  includes, at  102 , receiving data from a client at a client socket on networking device  18 . The method further includes, at  104 , creating an operating system-level event  58  in response to receiving the data. Typically, filter  54  is configured create the event upon detection of data entering socket  48 , as described above. The event is typically entered in event queue  56 . 
     At  106 , the method further includes detecting the event  58  from a component of a web server application program  32  executed on the networking device. As described above, the event is typically detected by a first or second accept state machine  62 ,  74 . Alternatively other components of web server application program  32  may be assigned this functionality, such as client session state machine  64 , server state machine  70 , or multiplexing agent state machine  68 . 
     At  108 , the method typically further includes, in response, reading data off of the socket with the web server application program, without polling the socket to determine whether data is ready to read on the socket. 
     At  110 , the method typically includes sending the data to a target web server  14 , via a target server socket. At  112 , the method typically includes, in response to the sent data, receiving data from the target server  14  at the networking device  18 , via the target server socket. At  114 , the method typically includes forwarding the data received from the target server, from the networking device to the client via the client socket. 
     Method  100  may also include multiplexing the data from a number of client sessions handled by client session state machines to one of a smaller number of server sessions handled by server session state machines. Typically, the multiplexing is accomplished using multiplexing agents, as described above. The multiplexing agent is typically associated with a client session and at least one server session. Data traveling to and from a single client may be sent to a target server via one of a plurality of target server sockets, using the multiplexing agents as described above with reference to  FIGS. 4-5 . 
     According to another embodiment of the invention, a method for processing data received from a computer network by a networking device may be practiced. The method typically includes receiving data from a network at a networking device, temporarily storing the data on a socket of the networking device, and detecting the data stored on the socket using an operating system-level software component, and alerting an application-level process that data is ready to be read on the socket by creating an operating system-level signaling event. The method further typically includes detecting the event at the application level, and, in response, reading the data from the socket via the application-level process. 
     According to the embodiments of the present invention, faster networking devices, methods, and software architectures may be implemented for use with web technologies. Speed improvements are realized due to a number of factors. In particular, the event-based signaling mechanisms for alerting an application that data is ready on a socket, the state machine architecture of the web server application program components, and the use multiplexing state agents all contribute to improved performance for the devices, methods, and architectures described herein. 
     While the present invention has been particularly shown and described with reference to the foregoing preferred embodiments, those skilled in the art will understand that many variations may be made therein without departing from the spirit and scope of the invention as defined in the following claims. The description of the invention should be understood to include all novel and non-obvious combinations of elements described herein, and claims may be presented in this or a later application to any novel and non-obvious combination of these elements. Where the claims recite “a” or “a first” element or the equivalent thereof, such claims should be understood to include incorporation of one or more such elements, neither requiring nor excluding two or more such elements.