[SYCL] Guard access to the cache of device lib programs

We cache device library programs (like fallback assertion) in the
context. In multi-threaded applications simultaneous access to the
cache of device lib programs is possible in program_manager::build().
That's why access to the this cache needs to be guarded to avoid data
race.

Author: againull

sycl/source/detail/context_impl.hpp

@@ -140,6 +140,9 @@ class context_impl {
   /// reference.
   const std::vector<device> &getDevices() const { return MDevices; }
 
+  using CachedLibProgramsT =
+      std::map<std::pair<DeviceLibExt, RT::PiDevice>, RT::PiProgram>;
+
   /// In contrast to user programs, which are compiled from user code, library
   /// programs come from the SYCL runtime. They are identified by the
   /// corresponding extension:
@@ -151,10 +154,10 @@ class context_impl {
   /// See `doc/design/DeviceLibExtensions.rst' for
   /// more details.
   ///
-  /// \returns a map with device library programs.
-  std::map<std::pair<DeviceLibExt, RT::PiDevice>, RT::PiProgram> &
-  getCachedLibPrograms() {
-    return MCachedLibPrograms;
+  /// \returns an instance of sycl::detail::Locked which wraps a map with device
+  /// library programs and the corresponding lock for synchronized access.
+  Locked<CachedLibProgramsT> acquireCachedLibPrograms() {
+    return {MCachedLibPrograms, MCachedLibProgramsMutex};
   }
 
   KernelProgramCache &getKernelProgramCache() const;
@@ -179,8 +182,8 @@ class context_impl {
   PlatformImplPtr MPlatform;
   property_list MPropList;
   bool MHostContext;
-  std::map<std::pair<DeviceLibExt, RT::PiDevice>, RT::PiProgram>
-      MCachedLibPrograms;
+  CachedLibProgramsT MCachedLibPrograms;
+  std::mutex MCachedLibProgramsMutex;
   mutable KernelProgramCache MKernelProgramCache;
   mutable PropertySupport MSupportBufferLocationByDevices;
 };

sycl/source/detail/program_manager/program_manager.cpp

@@ -568,7 +568,7 @@ RT::PiProgram ProgramManager::getBuiltPIProgram(
     ProgramPtr BuiltProgram =
         build(std::move(ProgramManaged), ContextImpl, CompileOpts, LinkOpts,
               getRawSyclObjImpl(Device)->getHandleRef(),
-              ContextImpl->getCachedLibPrograms(), DeviceLibReqMask);
+              ContextImpl->acquireCachedLibPrograms().get(), DeviceLibReqMask);
 
     emitBuiltProgramInfo(BuiltProgram.get(), ContextImpl);
 
@@ -1900,7 +1900,7 @@ device_image_plain ProgramManager::build(const device_image_plain &DeviceImage,
     ProgramPtr BuiltProgram =
         build(std::move(ProgramManaged), ContextImpl, CompileOpts, LinkOpts,
               getRawSyclObjImpl(Devs[0])->getHandleRef(),
-              ContextImpl->getCachedLibPrograms(), DeviceLibReqMask);
+              ContextImpl->acquireCachedLibPrograms().get(), DeviceLibReqMask);
 
     emitBuiltProgramInfo(BuiltProgram.get(), ContextImpl);