locking is required around pj_init_plus (partial revert of 2063) as it appears pj_init_plus will fail under high concurrent load even with proj 4.7.0 (only seen when reprojecting data) and will likely require use of a context (available in next release) if we wish to remove locks

CHANGELOG

@@ -24,7 +24,7 @@ Mapnik Trunk
 
 - Added xinclude (http://www.w3.org/TR/xinclude/) support to libxml2-based xml parser (oldtopos) (#567)
 
-- Optimized rendering speeds by avoiding locking in the projection code (r2063)
+- Optimized rendering speeds by avoiding locking in the projection code (r2063) (r2713)
 
 - Added support for setting global alignment of polygon pattern fills (#203)
 
@@ -115,9 +115,9 @@ Mapnik 0.7.0 Release
 
 - Shape Plugin: Fixed missing compiler flags that causes crashing on newer g++ versions (#436)
 
-- PNG: Fixed problem with garbled/striped png256 output along sharpe edges(#416,#445,#447,#202)
+- PNG: Fixed problem with garbled/striped png256 output along sharp edges(#416,#445,#447,#202)
 
-- PNG: Added support for semitransparency in png256 output (#477,#202)
+- PNG: Added support for semi-transparency in png256 output (#477,#202)
 
 - PolygonSymbolizer: Added 'gamma' attribute to allow for dilation of polygon edges - a solution
   to gap artifacts or "ghost lines" between adjacent polygons and allows for slight sharpening of

src/projection.cpp

@@ -124,10 +124,14 @@ projection::~projection()
     
 void projection::init()
 {
-// http://trac.osgeo.org/proj/wiki/ThreadSafety
-#if PJ_VERSION < 470 && MAPNIK_THREADSAFE
+// Based on http://trac.osgeo.org/proj/wiki/ThreadSafety
+// you could think pj_init was threadsafe in version 4.7.0
+// but its certainly not, and must only be in >= 4.7 with
+// usage of projCtx per thread
+//#if PJ_VERSION < 470 && MAPNIK_THREADSAFE
+//    mutex::scoped_lock lock(mutex_);
+//#endif
     mutex::scoped_lock lock(mutex_);
-#endif
     proj_=pj_init_plus(params_.c_str());
     if (!proj_) throw proj_init_error(params_);
     is_geographic_ = pj_is_latlong(proj_) ? true : false;