Micro Focus Visual COBOL 2.3 Update 2 for Eclipse (Windows) > Programming > Data Access > File Handling > Fileshare Guide > Introduction > How Fileshare Works

How Fileshare Works

Using the base COBOL file handling system, a typical COBOL I/O request to a shared data file causes the file handler to make several accesses to that data file across the network. See Figure 1.

Figure 1. Conventional Network

With Fileshare, a program that needs to access a data file has its request processed by the File Handling Redirector (FHRedir) module. The FHRedir module sends the request over the network to a Fileshare Server that performs the low-level I/O operations and then passes the result of the I/O operation, including the file status, back to FHRedir. FHRedir returns the result to the program. See Figure 2.

Figure 2. Fileshare Network

A Fileshare System is made up of:

Fileshare Clients	A Fileshare Client comprises a user program, making data file I/O requests, via the FHRedir module. FHRedir redirects the I/O requests to a Fileshare Server.
Fileshare Servers	A Fileshare Server runs on the same machine as the data files that you want to access. The Fileshare Server accepts requests across the network from the Fileshare Client, processes them by calling a local copy of the Micro Focus File Handler and then returns the result to the Fileshare Client.

Note:

The Fileshare Server and the Fileshare Client can be running on the same physical machine. For example, with a multi-tasking operating system such as Windows, the Fileshare Client can run in one session and the Fileshare Server can run in another session. Using this method, you can develop Fileshare applications on a single PC without actually sending data across a network. You should be aware, however, that performance improvements will not be observed, as no network is being used.
You can also run the Fileshare Server in the same session as the Fileshare Client using the single user mode of operation. This enables you to take advantage of advanced Fileshare features, such as transaction processing, without the need for a network or multiple sessions. For more information on the single user mode of operation, see the section Single User Mode in the chapter Advanced Operations.

Since a single Fileshare Server processes all the requests from several Fileshare Clients, it can use a single copy of the Micro Focus File Handler, regardless of how many users are accessing the Fileshare Server. This has several advantages:

The Fileshare Server can open the data files exclusively making full use of both its own cache and the operating system's cache
The Fileshare Server does not need to obtain semaphores on the data file. Normally semaphores are needed to control concurrent access to shared data files.
The Fileshare Server can process record locks internally without the need to make calls to the operating system