/// <summary>
/// Tries to fulfill the specified <paramref name="demand"/>. Adds the result to <see cref="Selections"/> if successful.
/// </summary>
/// <returns><c>true</c> if the demand could be met, <c>false</c> if not.</returns>
protected bool TryFulfill(SolverDemand demand)
{
var candidates = GetCompatibleCandidates(demand);
var existingSelection = Selections.GetImplementation(demand.Requirements.InterfaceUri);
if (existingSelection == null)
{ // Try to make new selection
return(TryFulfill(demand, candidates));
}
else
{ // Try to use existing selection
// Ensure existing selection is one of the compatible candidates
if (candidates.All(x => x.Implementation.ID != existingSelection.ID))
{
return(false);
}
if (!existingSelection.ContainsCommand(demand.Requirements.Command))
{ // Add additional command to selection if needed
var command = existingSelection.AddCommand(demand.Requirements, from: CandidateProvider.LookupOriginalImplementation(existingSelection));
return((command == null) || TryFulfill(DemandsFor(command, demand.Requirements.InterfaceUri)));
}
return(true);
}
}
/// <summary>
/// Gets all <see cref="SelectionCandidate"/>s for the <paramref name="demand"/> that are compatible with the current <see cref="Selections"/> state.
/// </summary>
private IEnumerable <SelectionCandidate> GetCompatibleCandidates(SolverDemand demand) => demand.Candidates.Where(candidate =>
{
if (!candidate.IsSuitable)
{
return(false);
}
var nativeImplementation = candidate.Implementation as ExternalImplementation;
// Ensure the candidate does not conflict with restrictions of existing selections
foreach (var restriction in Selections.RestrictionsFor(demand.Requirements.InterfaceUri))
{
// Prevent mixing of 32-bit and 64-bit binaries
if (candidate.Implementation.Architecture.Cpu.Is32Bit() && Selections.Is64Bit)
{
return(false);
}
if (candidate.Implementation.Architecture.Cpu.Is64Bit() && Selections.Is32Bit)
{
return(false);
}
if (restriction.Versions != null && !restriction.Versions.Match(candidate.Version))
{
return(false);
}
if (nativeImplementation != null && !restriction.Distributions.ContainsOrEmpty(nativeImplementation.Distribution))
{
return(false);
}
}
// Ensure the existing selections do not conflict with restrictions of the candidate
foreach (var restriction in candidate.Implementation.GetEffectiveRestrictions())
{
var selection = Selections.GetImplementation(restriction.InterfaceUri);
if (selection != null)
{
if (restriction.Versions != null && !restriction.Versions.Match(selection.Version))
{
return(false);
}
if (nativeImplementation != null && !restriction.Distributions.ContainsOrEmpty(nativeImplementation.Distribution))
{
return(false);
}
}
}
return(true);
});
protected override bool TryFulfill(SolverDemand demand, IEnumerable <SelectionCandidate> candidates)
{
foreach (var selection in candidates.ToSelections(demand))
{
Selections.Implementations.Add(selection);
if (TryFulfill(DemandsFor(selection, demand.Requirements)))
{
return(true);
}
else
{
Selections.Implementations.RemoveLast();
}
}
if (_backtrackCounter++ >= MaxBacktrackingSteps)
{
throw new SolverException("Too much backtracking; dependency graph too complex.");
}
return(false);
}
/// <summary> /// Tries to fulfill the specified solver demand. Adds the result to <see cref="Selections"/> if successful. /// </summary> /// <param name="demand">The demand to fulfill.</param> /// <param name="candidates">The candidates to consider for fulfilling the demand.</param> /// <returns><c>true</c> if the demand could be met, <c>false</c> if not.</returns> protected abstract bool TryFulfill(SolverDemand demand, IEnumerable <SelectionCandidate> candidates);
/// <summary> /// Turns <see cref="SelectionCandidate"/>s into <see cref="ImplementationSelection"/>s. /// </summary> /// <param name="candidates">The selection candidates.</param> /// <param name="demand">The solver demand the candidates were chosen for.</param> public static IEnumerable <ImplementationSelection> ToSelections(this IEnumerable <SelectionCandidate> candidates, SolverDemand demand) => candidates.Select(x => x.ToSelection(demand.Requirements, allCandidates: demand.Candidates));
