On 03.09.2012 20:47, Stefan Küng wrote: > Hi, > > It seems that the svn_config_t structure isn't thread safe, i.e. can't > be shared among multiple threads. > See here for a detailed report on what problems this causes: > http://tortoisesvn.tigris.org/ds/viewMessage.do?dsForumId=757&dsMessageId=3003152 > > > Is this by design? I assumed that all svn APIs are thread safe for > read access at least unless noted otherwise (example: the API > svn_utf_initialize states its thread-unsafeness in the note section of > the docs).
Subversion's functions are re-entrant. Data structures, including svn_config_t, are thread-specific. We don't promise any more than that. > While we can work around that thread problem a little bit, that > workaround has its own big problems: > * each thread would need its own svn_config_t structure > --> for each thread the config file is read (open, read, close) > which results in multiple unnecessary disk accesses One would assume that the config file is contents are cached once they've been read, so disk accesses shouldn't be an issue. > --> when the config file is read multiple times, sometimes the read > fails (at least on Windows) because the file is opened already - > usually because virus scanners open and scan every file that a > process accesses, even when only for reading. So we have to add a delay loop. Why a file that has not been changes should be locked by virus scanners is, IMO, an issue to be taken up with Windows virus scanner writers. Also, one can always use a mutex to control access to the svn_config_t. Surely that's preferable to re-reading it any number of times. > Joel Jirak made a patch for subversion/libsvn_subr/config.c which > would fix the problem (see the thread linked above). Would that be an > acceptable solution? The patch creates a new pool for almost every access, so no, that's not acceptable. The only way to make this work would be to rev all the svn_config_* global APIs to accept a scratch pool argument from which allocations should be made. Either that, or add a new API that creates a deep-copy of the in-memory svn_config_t structure, making this another way to avoid re-reading the config file for each thread and avoiding the hassle of managing a mutex. -- Brane -- Certified & Supported Apache Subversion Downloads: http://www.wandisco.com/subversion/download
