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PHP RFC: Native TLS
- Version: 1.0
- Date: 2014-11-19
- Author: Anatol Belski, email@example.com
- Status: Draft /* (or Under Discussion or Accepted or Declined) */
/* * First Published at: http://wiki.php.net/rfc/your_rfc_name */
Currently, to access module globals in TS mode, a global resource array is used. That array contains globals from all the threads and per thread globals are identified by the thread key. The thread key is passed to every function requiring access to the globals. Or, it has to be fetched on demand. Consequently
- many functions have to take an additional argument used only in TS mode, that makes code to be overloaded with TSRMLS_* macros
- forgetting to declare/pass a TS parameter wouldn't do any harm in NTS mode (as those are all macros), but may cause build breach in the TS
- additionally it might introduce some C89 incompatibility in NTS mode when TSRMLS_FETCH() is used before var declarations
- in some cases TS related code has to be explicitly conditioned with preprocessor directives (#ifdef ZTS)
- when the thread id isn't passed directly, TSRMLS_FETCH() has to be used, which is slow
This RFC bases on https://wiki.php.net/rfc/tls , however I don't mention it under the “First Published” position. While the key points are the same, the patch and the meaning undergone some changes. Still teh base RFC contains a lot of useful info about cross platform compatibility and various TLS implementations, so I would say it is useful to briefly read through it as well.
The technique of passing thread id explicitly should be removed where possible. Ideally, one global thread specific variable should be used to hold the thread key (while it's not possible exactly the way on every platform, see the implementation details).
The current patch focuses on stability and code quality improvement more than on performance. Whereby the latest tests show that the patched version is at least as fast as the mainstream.
Backward Incompatible Changes
- thread id will not be passed explicitly anymore, many signatures have to loose their TSRM_* parts
- a few places with “#ifdef ZTS” have to be reworked to fetch the thread key the new way
The current implementation is done by the following scheme -
Proposed PHP Version(s)
Threading capable SAPIs may need to be reworked. Currently it regards only to Apache mpm_worker and mpm_winnt. See implemtation details.
To Existing Extensions
See implementation details.
The patch from the base RFC used an offset mechanism instead of the array indexing to access globals. That part wasn't ported in the current patch as it has caused too much issues. This however should be still done as using offsets would speedup the data access.
Unaffected PHP Functionality
Userland is not affected, the change is internals only.
- faster data access using offsets instead of array indexes
- depending on compiler evolution, fetching thread id per function could be replaced with a real global variable shared across all the binary units (.so, .dll, .exe)
Proposed Voting Choices
50%+1 majority required
Patches and Tests
Keep this updated with features that were discussed on the mail lists.*/