Method and system for controlling data flow

• US 6,032,188 A
• Filed: 03/12/1997
• Issued: 02/29/2000
• Est. Priority Date: 03/12/1997
• Status: Expired due to Term

• Current Assignee: Picturetel Corporation (HP Inc.), Microsoft Technology Licensing LLC (Microsoft Corporation)
• Original Assignee: Picturetel Corporation (HP Inc.), Microsoft Corporation
• Inventors: May, Philip, Mairs, Christopher J.
• Primary Examiner(s): Asta, Frank J.
• Assistant Examiner(s): YUAN, ALMARI ROMERO
• Application Number:
  US08/815,091
• Time in Patent Office: 1,084 Days
• Field of Search: 709/226, 709/234, 709/235, 709/213, 709/104, 709/105, 370/229, 370/232, 370/234, 370/235
• US Class Current: 709/234
• CPC Class Codes: G06F 3/14 Digital output to display device ; Cooperation and interconnection of the display device with other functional units
• CPC Class Codes: G06F 9/52 Program synchronisation; Mutual exclusion, e.g. by means of semaphores

Abstract

A method and system for controlling flow of output data between computers sharing an application program. The application program is executed on a host computer and shared with shadow computers. Each computer has a sharing system for coordinating the sharing of the application program. The sharing system of the host computer requests a flow control system of the host computer for permission to transmit output data. The flow control system of the host computer, upon receiving the request for permission, determines whether the amount of output data currently in transit from the host computer to the shadow computers exceeds the amount that can be in transit. When the amount is not exceeded, the flow control system grants permission to the sharing system of the host computer; and when the amount is exceeded, the flow control system denies permission to the sharing system of the host computer. Periodically, the flow control system calculates a shadow display time that represents time needed to transmit a certain amount of output data to the shadow computers and to process the certain amount of output data at the shadow computers. The flow control system also adjusts the amount of data that can be in transit when the calculated shadow display time is not acceptable so that the host computer and shadow computers can be displaying output data at approximately the same time. The sharing system transmits the output data to the shadow computers when permission is granted.

Claims

1. A method in a computer system for controlling flow of output data between computers sharing an application program, the application program being executed on a host computer and shared with shadow computers, each computer having a sharing system for coordinating the sharing of the application program, the method comprising:

under control of the sharing system of the host computer, requesting a flow control system of the host computer for permission to transmit the output data to all of the shadow computer; and

under control of the flow control system of the host computer,

upon receiving the request for permission,

determining whether the amount of output data currently in transit from the host computer to all of the shadow computers exceeds an amount that can be in transit;

when the amount is not exceeded, granting permission to the sharing system of the host computer; and

when the amount is exceeded, denying permission to the sharing system of the host computer; and

periodically calculating a shadow display time that represents a time needed to allow for the transmitting of a certain amount of the output data to all of the shadow computers and to allow all of the shadow computers to process the certain amount of the output data; and

using the shadow display time to determine the amount of the data that can be transmitted to all of the shadow computers within given time segments so that the host computer and all of the shadow computers can be displaying transmitted amounts of the output data at approximately the same time; and

under control of the sharing system, when permission is granted, transmitting the output data to all of the shadow computers in the determined amount.

2. The method of claim 1 wherein the calculating of the shadow display time includes transmitting a data notification message to the flow control system of each shadow computer and wherein the flow control system of each shadow computer transmits a notification acknowledgment message to the flow control system of the host computer when the sharing system of the shadow computer is ready to receive more output data and the data notification message has not yet been acknowledged.

3. The method of claim 2 including:

under control of the flow control system of the host computer, when permission was previously denied and upon receiving a notification acknowledgment message from the flow control system of each shadow computer, notifying the sharing system of the host computer that the output data can now be transmitted.

4. The method of claim 1 wherein the amount of data that can be transmitted with the given time segments is decreased when the shadow display time is larger than acceptable and is increased when the shadow display time is smaller than acceptable.

5. A method for controlling flow of output data between computers sharing an application program, the application program being executed on a host computer and shared with shadow computers, the method comprising:

transmitting amounts of the output data from the host computer to all of the shadow computers within given time segments;

determining a shadow display time representing the time it takes for all of the shadow computers to receive and display transmitted amounts of the output data;

when the shadow display time is greater than an acceptable time, decreasing the amount of the output data that can be transmitted from the host computer to all of the shadow computers within the given time segment; and

when the shadow time is less than the acceptable time, increasing the amount of the output data that can be transmitted from the host computer to all of the shadow computers within the given time segments.

6. The method of claim 5 wherein each computer has a sharing system for coordinating the sharing of the application program, the sharing system of the host computer having a flow control system that calculates the shadow display time and adjusts the amount of data that can be transmitted within the given time segments.

7. The method of claim 5 wherein each computer has a sharing system for coordinating the sharing of the application program, each sharing system having a flow control system, wherein a shadow sharing system of a shadow computer notifies a shadow control system of the shadow computer when output data has been displayed, and wherein upon being notified, the shadow flow control system notifies a host flow control system of the host computer so that the host flow control system can calculate the shadow display time.

8. A computer-readable medium containing instructions for causing a computer system to control flow of output data between computers sharing an application program, the application program being executed on a host computer and shared with shadow computers, the instructions performing the steps comprising:

determining a shadow display time representing a time it takes for all of the shadow computers to receive and display an amount of the output data transmitted to all of the shadow computers by the host computer;

when the shadow display time is not within a predetermined range, adjusting the amount of the output data that can be transmitted within a given time unit from the host computer to all of the shadow computers; and

delaying transmission of the adjusted amount of the output data when the total amount of data to be transmitted between the host computer and all of the shadow computers would exceed a predetermined limit so that the shadow computers can be displaying the same output data as the host computer.

9. The computer-readable medium of claim 8 wherein each computer has a sharing system for coordinating the sharing of the application program, the sharing system of the host computer having a flow control system that calculates the shadow display time and that adjusts the amount of data that can be in transit.

10. The computer-readable medium of claim 8 wherein each computer has a sharing system for coordinating the sharing of the application program, each sharing system having a flow control system, wherein a shadow sharing system of a shadow computer notifies a shadow control system of the shadow computer when output data has been displayed, and wherein upon receiving the notification, the shadow flow control system notifies a host flow control system of the host computer so that the host flow control system can calculate the shadow display time.

11. A method for controlling flow of output data between computers sharing an application program, the application program being executed on a host computer and shared with shadow computers, the method comprising:

transmitting an amount of the output data from the host computer to all of the shadow computers within a given time segment;

determining a time representing the time it takes for all of the shadow computers to receive and display the transmitted output data; and

when the determined time is not acceptable, adjusting the amount of the output data that can be transmitted from the host computer to all of the shadow computers within the given time segment.