private ViewCompilerWorkItem CreatePrecompiledWorkItem(string normalizedPath, CompiledViewDescriptor precompiledView)
{
// We have a precompiled view - but we're not sure that we can use it yet.
//
// We need to determine first if we have enough information to 'recompile' this view. If that's the case
// we'll create change tokens for all of the files.
//
// Then we'll attempt to validate if any of those files have different content than the original sources
// based on checksums.
if (precompiledView.Item == null || !CustomChecksumValidator.IsRecompilationSupported(precompiledView.Item))
{
return(new ViewCompilerWorkItem()
{
// If we don't have a checksum for the primary source file we can't recompile.
SupportsCompilation = false,
ExpirationTokens = Array.Empty <IChangeToken>(), // Never expire because we can't recompile.
Descriptor = precompiledView, // This will be used as-is.
});
}
var item = new ViewCompilerWorkItem()
{
SupportsCompilation = true,
Descriptor = precompiledView, // This might be used, if the checksums match.
// Used to validate and recompile
NormalizedPath = normalizedPath,
ExpirationTokens = GetExpirationTokens(precompiledView),
};
// We also need to create a new descriptor, because the original one doesn't have expiration tokens on
// it. These will be used by the view location cache, which is like an L1 cache for views (this class is
// the L2 cache).
item.Descriptor = new CompiledViewDescriptor()
{
ExpirationTokens = item.ExpirationTokens,
Item = precompiledView.Item,
RelativePath = precompiledView.RelativePath,
};
return(item);
}
private Task <CompiledViewDescriptor> OnCacheMiss(string normalizedPath)
{
ViewCompilerWorkItem item;
TaskCompletionSource <CompiledViewDescriptor> taskSource;
MemoryCacheEntryOptions cacheEntryOptions;
// Safe races cannot be allowed when compiling Razor pages. To ensure only one compilation request succeeds
// per file, we'll lock the creation of a cache entry. Creating the cache entry should be very quick. The
// actual work for compiling files happens outside the critical section.
lock (_cacheLock)
{
// Double-checked locking to handle a possible race.
if (_cache.TryGetValue(normalizedPath, out Task <CompiledViewDescriptor> result))
{
return(result);
}
if (_precompiledViews.TryGetValue(normalizedPath, out var precompiledView))
{
_logger.ViewCompilerLocatedCompiledViewForPath(normalizedPath);
item = CreatePrecompiledWorkItem(normalizedPath, precompiledView);
}
else
{
item = CreateRuntimeCompilationWorkItem(normalizedPath);
}
// At this point, we've decided what to do - but we should create the cache entry and
// release the lock first.
cacheEntryOptions = new MemoryCacheEntryOptions();
Debug.Assert(item.ExpirationTokens != null);
for (var i = 0; i < item.ExpirationTokens.Count; i++)
{
cacheEntryOptions.ExpirationTokens.Add(item.ExpirationTokens[i]);
}
taskSource = new TaskCompletionSource <CompiledViewDescriptor>(creationOptions: TaskCreationOptions.RunContinuationsAsynchronously);
if (item.SupportsCompilation)
{
// We'll compile in just a sec, be patient.
}
else
{
// If we can't compile, we should have already created the descriptor
Debug.Assert(item.Descriptor != null);
taskSource.SetResult(item.Descriptor);
}
_cache.Set(normalizedPath, taskSource.Task, cacheEntryOptions);
}
// Now the lock has been released so we can do more expensive processing.
if (item.SupportsCompilation)
{
Debug.Assert(taskSource != null);
if (item.Descriptor?.Item != null &&
CustomChecksumValidator.IsItemValid(_projectEngine.FileSystem, item.Descriptor.Item))
{
// If the item has checksums to validate, we should also have a precompiled view.
Debug.Assert(item.Descriptor != null);
taskSource.SetResult(item.Descriptor);
return(taskSource.Task);
}
_logger.ViewCompilerInvalidingCompiledFile(item.NormalizedPath);
try
{
var descriptor = CompileAndEmit(normalizedPath);
descriptor.ExpirationTokens = cacheEntryOptions.ExpirationTokens;
taskSource.SetResult(descriptor);
}
catch (Exception ex)
{
taskSource.SetException(ex);
}
}
return(taskSource.Task);
}