[fpc-devel] Rather large flaw in TJSONConfig component

[Hans-Peter Diettrich]

Graeme Geldenhuys schrieb:

> FPC finally has a working TMultiReadExclusiveWriteSynchronizer
> implementation (tiOPF implemented it's own), but I don't know if that
> implementation is available for FPC 2.4.x yet, or if it is still only in
> Trunk.  Either way, TXXXConfig classes could use the same synchronizer to
> manage access - with a bit of refactoring.

I don't see how this can be useful. Either the first user keeps the file 
open for writing, so that every other request will fail, or the file is 
closed after reading, so that any number of writes can follow.

For source code we have several VCS, which try to keep the files 
consistent, but even these fail to merge multiple changes from time to 
time. And such systems are quite useless with other (config) data, where 
little context is available for synchronization attempts - here the XML 
format provides the most context information, with best chances for 
successful merges. In either case every update should read the current 
file contents, and merge it with the local changes before writing the 
entire file back to disk. Then also writelocks make sense, so that only 
one update can be applied after another.

DoDi