JPH08202665A - Inter-computer coupling device of loosely coupled computer - Google Patents

Abstract

PURPOSE: To provide an inter-computer coupling device, which actualizes a fast broadcasting communication guaranteeing reliability, at a low cost for a network communication system. CONSTITUTION: A loosely coupled computer system is provided with a resend- requesting lock flag 113, which can be referred to by all computers on a network, and a counter 112 in the inter-computer coupling device, and each time the flag is referred to by a computer, the contents of the counter 112 are advanced by one. Further, history information on broadcasting is stored in lock information storage means 108 in all the computers. Consequently, the reliability of broadcasting communication can be guaranteed with small network resources and network packets required for mutual exclusion can be decreased.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a network construction method and its control method in a loosely coupled computer system.

[0002]

2. Description of the Related Art Conventionally, in a loosely coupled computer system,
There was a method of mutual exclusion while exchanging messages between computers. For example, various algorithms are introduced in a paper "Distributed Algorithm, Tsunehiko Kameda / Masashi Yamashita, Modern Science Co., Ltd., 1994". All of these distributed lock methods are realized using one-to-one message communication. In these methods, it is necessary to send a message to a computer that may acquire the lock and wait for all the messages to be returned. For example, in the Ricart-Agrawal algorithm, assuming that the number of computers requesting lock is N, 2 (N-1) messages are required to perform one lock / unlock, and N- One message is sent centrally to the computer that requested the lock. Since the processing is sequentially performed in one node, there is a problem that the completion of the lock request increases in proportion to the number N of computers that hold locks.

As described above, in the distributed lock algorithm, a message is sent to all the nodes that may set the lock. There is a method of realizing the operation of sending a message to all the nodes by a broadcast function using the support of hardware. For example,
Currently, LANs such as Ethernet, which are widely used, are provided with a broadcast function. However, even in the broadcast message, in order to confirm the arrival of the message,
It is necessary to guarantee that the message has arrived for the computers that have sent the simultaneous broadcast. It is conceivable that the computer that receives the simultaneous broadcast will send a message for confirmation response to the computer that sent the simultaneous broadcast, but this method causes a problem in the one-to-one communication as described above. Similarly, the processing amount becomes large.

In order to solve this problem, a method has been proposed in which a message is requested to be retransmitted only when a broadcast message has not arrived. MF Kaashoek et al. "An Efficient Reliable Broadcast", Operat
ing Systems Review, Vol.23, Oct.1989, pp.5-19. In this method, a computer (sequencer) that manages the order of broadcasts is determined in advance, and the computer that issues the broadcasts requests the broadcasts to computers with sequencers. When receiving the broadcast, it does not acknowledge the broadcast and requests the sequencer to retransmit only when a missing received packet is found.

[0005]

The method described in the conventional example has the following problems.

The first problem is that the method of MF Kaashoek et al. Sends a message to the sequencer once, and therefore requires two round-trip messages. In addition, the order in which the simultaneous broadcasts issued by the own computer are present can be known only when the simultaneous broadcasts arrive at the own computer from the computer serving as the sequencer. Therefore, when the lock is realized by the simultaneous broadcast communication, the lock request is kept waiting until the simultaneous broadcast communication is requested to the sequencer and the simultaneous broadcast is received from the sequencer.

A second problem is that the sequencer needs to retransmit a missing packet, and therefore it is necessary to have history information of broadcast messages. If a computer with history information, that is, a sequencer, fails, history information for simultaneous broadcast is lost,
It becomes difficult to guarantee the message loss.

[0008]

In order to solve the above problems, according to the present invention, at least two flags that can be referred to by all the connected computers are provided in the inter-computer coupling device, and the computer is connected to the network. At least one counter that can be referred to from all the computers that have been referred to is provided, and this counter is characterized in that the content of the counter is incremented by one each time it is referred. By providing this counter, it is possible to reduce the number of messages, which was required at the time of the numbering of the simultaneous broadcast communication, which is the first problem, to two. The second problem is that all computers have history information for simultaneous broadcast, so that even if any computer fails, another computer can substitute it. However, in this case, if a retransmission request transmitted by broadcast is transmitted to all the computers, a retransmission packet is received from all the computers, which causes a third problem that the number of messages increases. In order to avoid such retransmission from all computers, all computers can refer to
By giving one flag, the number of retransmitted computers is limited to one.

[0009]

According to the present invention, in a network communication system, it is possible to inexpensively realize an inter-computer coupling device which realizes a simultaneous broadcast communication which guarantees reliability.

[0010]

FIG. 1 shows one embodiment of the loosely coupled computer system according to the present invention. The loosely coupled computer system includes a plurality of computers 101 and a computer coupling device 110 that connects the computers 101. Each computer 101 includes a processor 104, an auxiliary storage device 105, and a main memory 10.
6, a network interface 107, and a lock information storage means 108. Computer coupling device 110
Is a network interface 111 for connecting the computers 101 and a packet switching network 11 for interconnecting the network interfaces 111 to exchange packets.
5, and a counter 112 and a retransmission request lock flag 113 that can be referred to by the processor 104 of each computer 101 via each network interface 111. The computer coupling device 110 has a broadcast function for transmitting a packet from one computer 101 to all other computers. This broadcast function is introduced as a well-known example on page 101 of "Parallel Computer Construction, Shinji Tomita, Shokodo". Counter 112
Has a function of reading the value of the counter by a read command from each computer, sending it back to the computer that issued the request, and then incrementing the content of the counter by one. For example, TT
It can be configured by a logic circuit such as L or CMOS. The resend request lock flag 113 has a TestAndSet function. The TestAndSet function is a well-known technique, for example, “Basics of Operating System, A.
N. Page 73 of "Haberman, Translated by Norihisa Doi, Baifukan". This TestAndSet function reads the previous value of the lock flag 113, and if it is 0,
The value of the lock flag 113 is set to 1, and the previous value 0 is read. If the value of the lock flag 113 is 1, the value of the lock flag is set to 1 as it is. By allowing the above operations to be performed at one time without being disturbed by other operations, the lock flag can be used exclusively. The retransmission request lock flag 113 is a well-known technique, and is a TTL or CMO.
It can be configured by a logic circuit such as S. The lock information storage means 108, as shown in FIG.
It may be independently connected to the system bus, or may be built in the main memory 106 or the network interface 107.

In the present invention, in order to request the lock and release the lock, the simultaneous broadcast function is used to perform communication between the computers 101 so that the lock information is the same for all computers. Guarantee. Generally, there is a packet loss of the simultaneous broadcast communication due to disturbance on the network, so it is necessary to compensate by retransmitting the dropped packet. The counter 112 and the retransmission request bit 113 are used to compensate for this packet loss. Hereinafter, in the present invention, a process in which the lock function operates using the counter 112 and the retransmission request bit 113 will be described with reference to a PAD diagram.

FIG. 2 shows an embodiment of the lock information storage means 108 in the present invention. The lock information storage means 108 includes a lock waiting queue 201, an execution counter 206, and a latest reception counter 207. Lock waiting queue 20
1 is configured as a queue including a sequence number 202, a lock ID 203, a lock request computer number 204, and a request process number 205. Execution counter 206
Indicates the latest computer number that executed the lock, and the latest reception counter 207 indicates the latest computer number that executed the lock request. The lock waiting queue 201 includes lock requests from all computers 101. Lock requests from other computers are notified by broadcast communication. If broadcast packets are not lost on the network, the lock request will be the same on all computers. However, as described above, packet loss may occur in an actual network. An object of the present invention is to provide a technique for compensating for this missing packet by the packet contents 208 in the lock waiting queue 201 of another computer.

FIG. 3 shows an embodiment of the contents of the packet for simultaneous broadcast communication used in the present invention. Broadcast packet 3
01 is composed of a packet header 302 and data 303. The packet header 302 is the sender computer 3
04, a packet type 305, and a sequence number 306. The sender computer 304 indicates the number of the computer that has sent the broadcast packet. There are the following three types of packet 305: lock request, unlock,
There is a resend request. Sequence number is computer coupling device 1
This is the value of the counter 112 in 10, and by using this number, the loss of the broadcast packet is detected by each computer.
The lock identifier 307 is prepared to request a plurality of types of locks. If all computers use one lock, this lock identifier is not needed.

The processing in each computer when transmitting or receiving the above three types of packets will be described below.

FIG. 4 is a PAD diagram showing a processing flow when a lock request is transmitted from an arbitrary computer according to the present invention. When there is a lock request, first, as shown in step 401, the contents of the counter 112 in the computer coupling device 110 are temporarily read into the main memory. Next, as shown in step 402, when the counter 112 is read, the value of the counter 112 is incremented by one. The value of the counter 112 read into the main memory 106 is calculated in step 40.
As shown in 3, the sequence number 306 in the packet header 302 is stored. Here, in step 404, if the value obtained by adding 1 to the execution counter 206 of the own computer is equal to the sequence number 306 in the packet header 302, it is known that there is no other computer that issued the lock request. In step 405, the fact that the lock request has been established is notified to the user process that made the lock request. Step 406
Then, the packet management information 209 is inserted into the lock waiting queue 201 of the own computer in order to indicate that the own computer has issued the lock request and has not released the lock request yet. The sequence number 202, the lock ID 203, and the lock request computer number 204 in the lock waiting queue 201 are the sequence number 305 and the sequence number 305 of the broadcast packet 301, respectively.
It corresponds to the lock identifier 307 and the sender computer 304.
The request process number 205 is used to store which process has made a request when receiving requests from a plurality of computers. For example, the process number in the UNIX operating system can be used instead.
For the process number of UNIX operating system, refer to "Design and Implementation of UNIX4.3BSD, SJL
effler et al., Translated by Akira Nakamura et al., Maruzen Co., Ltd. ”on page 25 for details. The order of inserting into the lock waiting queue 201 is the ascending order of the sequence numbers in the packet. In step 407, in order to notify another computer of the lock request of the own computer, the number of the own computer is stored in the sender computer 304, and after that, the sender computer 304 transmits the packet of the simultaneous broadcast communication. Through the above processing, the sender computer 304 notifies all computers of the lock request, and if there is no other request, the lock can be secured before notifying the lock request to other computers.

FIG. 5 is a PAD diagram showing a broadcast packet reception process in the present invention.

In step 501, the simultaneous broadcast communication is received,
The type of packet is checked in step 502. If the packet type is retransmission processing, retransmission processing is performed in step 503. Details of this retransmission processing will be described later. If there is no retransmission request, the latest reception counter 207 of the computer is incremented by 1 in step 504 and compared with the sequence number 306 in the packet. If smaller, it is determined that there is a packet loss and step 505. In, the resend request process is performed. Details of this retransmission request process will be described later. In step 506, the contents of the latest reception counter 207 of the own computer are set as the sequence number 306 in the packet, and the fact that the packet has been received without any packet loss is stored up to this packet. In step 507, the packet type is checked again, and if it is a lock request, the lock request is stored in the lock waiting queue 201. The position to insert the lock wait queue is
As described above, the sequence numbers in the packet are in ascending order. If the type of packet is unlocked in step 507, unlock receiving processing is performed in step 509. The details of the unlock reception processing will be described later.

FIG. 6 is a PAD diagram showing a retransmission request process according to the present invention. In the resending process, first, in step 601, the latest reception counter 207 of the own computer.
It is checked whether it is smaller than the value obtained by adding 1 to the value of the sequence number in the received packet. If it is smaller, it means that the broadcast packets having sequence numbers in between are missing. The following is a process of requesting that a missing packet be transmitted from another computer.
In step 602, the value of the resend request lock flag 111 in the computer coupling apparatus is checked by the TestAndSet function, and if the value obtained by the TestAndSet function is 1, another computer is in the process of resending, so wait as it is. to continue. If the value of TestAndSet is 0, it is found that there is no computer that is performing retransmission processing, and the process proceeds to step 603. In step 603, the type of the broadcast packet is set as a retransmission request, and the latest reception counter 207 of the own computer is set.
Broadcasting is performed using the value obtained by adding 1 to the sequence number as the sequence number. In step 604, the process waits until another computer retransmits the packet. Since the lock request requested by the own computer must be stored in the lock request waiting queue 201 of the own computer in step 406 of the lock request processing, even if the broadcast packet does not reach all the computers. , At least one computer can be guaranteed to have the lock request packet corresponding to the sequence number. Step 604 is a process of receiving the retransmitted packet. This step 60
The retransmission packet reception processing in 4 is realized by one-to-one communication with the retransmitting computer, and confirms the arrival of the packet, and sends an acknowledgment back to the retransmitting computer. In addition, there is a possibility that the broadcast communication for the resend request does not arrive at any of the computers. Therefore, assuming such a situation, a timer is set before the waiting process of step 604, and When the set time has elapsed, step 604 also includes the process of executing step 603 again. In step 605, the retransmitted packet is put in the head of the lock waiting queue 201. At step 606, the retransmission request lock bit 1
The value of 13 is set to 0. Finally, in step 607, 1 is added to the latest reception counter 207 of the own computer. If the counter value does not satisfy the condition of step 601, the processes of steps 602 to 606 are repeated again, and the missing packet is transmitted from another computer.
FIG. 7 is a PAD diagram showing a retransmission process in the present invention.
The computer that has received the resend request performs resend processing as follows. In step 701, the sequence number 202 in the lock waiting queue 201 is scanned, and if there is a sequence number 202 that is equal to the sequence number for which a resend request has been made, the process proceeds to step 702 and subsequent steps. If it does not exist, the retransmission process is terminated. In step 702, it is checked whether or not the packet corresponding to the sequence number 202 found in step 701 is transmitted from the computer. If the corresponding packet is transmitted from the computer, in step 703, step 701.
The packet corresponding to the result of the inspection in step 2 is transmitted to the retransmission request computer. As described above, the transmission process in step 701 is realized by using the one-to-one communication including the confirmation response process.

By the processing shown in FIG. 6 and FIG. 7, the lock request packet using the simultaneous broadcast communication can be held by all the computers, so that the lock information can be obtained even if any computer fails. It will be recoverable.

FIG. 8 is a PAD diagram showing the process of receiving the lock release request according to the present invention. In step 801, the execution packet counter and the sequence number in the packet are checked. If the value of the execution counter 206 and the sequence number in the packet are the same, it is known that there is lock information at the head of the lock wait queue 201, and that information is deleted. As shown in steps 802 and 803, the process of deleting the lock wait information is performed by the lock wait queue 2
This can be realized by the process of removing the head from 01. In step 804, it is checked whether or not the head of the lock waiting queue in the local computer is a request from the local computer. If so, in step 805, the lock can be acquired in the program for which the local computer has requested locking. Notify that.
In step 801, if the value of the execution counter 206 is not equal to the sequence number in the packet, the lock request packet is missing. Therefore, in step 806, the retransmission request process is performed, and then the step 801 is performed. The process of is repeated.

[0021]

According to the present invention, a plurality of computers are connected by a network, each computer has an independent address space, and a shared data memory for sharing data among a plurality of computers on a memory in each computer. In a loosely coupled computer system that has, it is possible to reduce network packets required for synchronization to guarantee consistency of shared data and synchronization for controlling parallel programs, so network resources can be effectively used. You can do it.
In addition, since the consistency of shared data can be guaranteed as well as the synchronization for controlling the parallel program, the burden on the programmer who writes the parallel program can be reduced. As a result, in particular, it becomes possible to efficiently deal with the problem of parallel processing in which the calculation time is longer than the communication time and it is difficult to automatically distribute the load.

[Brief description of drawings]

FIG. 1 is a block diagram of a loosely coupled computer system according to an embodiment of the present invention.

FIG. 2 is a diagram showing an embodiment of lock information storage means in the present invention.

FIG. 3 is a diagram showing an embodiment of a broadcast packet according to the present invention.

FIG. 4 is a PAD diagram showing a process of transmitting a broadcast packet at the time of locking in the present invention.

FIG. 5 is a PAD diagram showing a receiving process of a broadcast packet according to the present invention.

FIG. 6 is a PAD diagram showing retransmission request processing of a broadcast packet according to the present invention.

FIG. 7 is a PAD diagram showing retransmission processing of a broadcast packet according to the present invention.

FIG. 8 is a PAD diagram showing processing when a lock release packet is received in the present invention.

[Explanation of symbols]

100: Loosely Coupled Computer System, 101: Computer, 103: System Bus, 104: Processor, 105: Auxiliary Storage Device, 106: Main Memory, 107: Network Interface in Computer, 108: Lock Information Storage Means, 110: Between Computers Coupling device, 111: Network interface in computer coupling device, 112: Counter, 113: Retransmission request lock flag, 115: Packet switching network, 201: Lock wait queue, 202: Sequence number, 203: Lock ID, 204: Lock request Computer number, 205: Request process number, 206: Execution counter, 207: Latest reception counter, 301: Network packet, 302: Packet header, 303: Data in network packet, 304: Broadcast packet 305: Type of broadcast packet, 306: Sequence number of broadcast packet, 307: Lock identifier realized by broadcast packet, 401-407: Broadcast when locked Communication processing, 501 to 509: Reception processing of broadcast packet, 601 to 607: Processing for requesting retransmission of packet lost in broadcast communication, 701 to 703: Retransmission of packet lost in broadcast communication Processing, 801 to 805: lock release reception processing

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Satoshi Yoshizawa, Satoshi Yoshizawa, 1-280, Higashi Koikeku, Kokubunji, Tokyo Inside Hitachi Research Laboratory, Central Research Institute (72) Takehisa Hayashi 1-280, Higashi Koikeku, Kokubunji, Tokyo Hitachi, Ltd. Central Research Laboratory (72) Inventor Masahiro Kitano 810 Shimoimaizumi, Ebina, Kanagawa Stock Company Hitachi, Ltd. Office Systems Division

Claims (4)

[Claims] 1. A loosely coupled computer system in which computers are coupled via a network, which is a switching network for exchanging communication packets generated between the computers, and at least a counter which can be referred to by all the computers connected to the network. An inter-computer coupling device characterized by having one counter, incrementing the content of the counter by each reference, and having at least one flag that can be referenced by all the computers connected to the network. 2. A loosely coupled computer system having a computer-to-computer coupling device according to claim 1, wherein any one computer connected to the computer-to-computer coupling device sends a communication packet to all other computers. Claim 1 having a broadcast function
An inter-computer coupling device characterized in that the counter value read by the counter is included in the simultaneous broadcast communication packet. 3. A computer of the loosely coupled computer system according to claim 2, which stores a history of received broadcast communication packets and a counter value included in the received broadcast communication packets. And a means for comparing the counter value storage means stored in the header information of the received broadcast communication packet, the comparing means comprising:
The difference between the stored counter value and the counter value of the header information is 1
If not, the inter-computer coupling device is characterized in that it judges that the broadcast communication packet has not arrived. 4. The loosely coupled computer system according to claim 3, wherein when a broadcast packet including a counter value does not arrive at the receiving computer, a retransmission request is made using the broadcast communication, If the computer that received the resend request is the computer that sent the broadcast packet containing the counter value, resend the broadcast packet containing the counter value to the computer that issued the resend request. An inter-computer coupling device characterized by: