PRB: "Too Many Files" Open in FoxPro for Macintosh

• Microsoft FoxPro for Macintosh, versions 2.5x, 2.6a
• Microsoft Visual FoxPro for Macintosh, version 3.0b

SYMPTOMS

When several users are running a FoxPro for Macintosh application and using tables stored on a server, it is possible to receive the message:

   Too many files open

CAUSE

This indicates that there are not enough file handles on the server for the number of users and files that are open. This usually happens when the server is another Macintosh connected to through the AppleTalk services provided with the System Software. The absolute limit of file handles on a Macintosh is 342. Note that each user that opens a file on a server uses another file handle.

WORKAROUND

The following are suggestions that may help reduce the number of file handles being used on the server:

1. Place the application the local hard drive (on each workstation).

2. Use the TMPFILES setting in the CONFIG.FPM file to make sure that temporary files are going to the local hard drive (of each workstation).

3. Change the application so that tables and other files are only open as long as they are needed, instead of keeping them open throughout the application.

MORE INFORMATION

The following information was provided by Apple Developer Support on the maximum number of File Control Blocks (FCBs) available in the Macintosh Operating System File Manager, and therefore, the number of files that can be open at one time. This information only applies to System 7.x.

"While System 7 increases the number of FCBs as required, there is an absolute limit imposed by the File Manager. This limit is 342 FCBs and is documented in Inside Macintosh, File p. 2-81:

'The initial size of the FCB buffer is determined by the system startup

You can find the beginning of any particular FCB by adding the size of all preceding FCBs to the size of the FCB buffer length word (that is, 2). This offset from the head of the FCB buffer is used as the file reference number of the corresponding open file. Because the current size of an FCB is 94 bytes, the first few valid file reference numbers are 2, 96, 190, 284, 378, 472, and so on. The maximum size of an expandable FCB buffer is 32,535 bytes, so there is an absolute limit of 342 FCBs in the FCB buffer.' "