don't rely on weakref being null, fix blobcache

- Checking weakref value to be null as an indicator of gc is not reliable. We probably need a finalizer for that, but all finalizers don't get called immediately at the moment (ref: JuliaLang/julia#13995). Going without that optimization for now.
- fixed an issue where cache eviction was corrupting the cache

src/blob.jl

@@ -315,8 +315,7 @@ function load_local(collid::UUID, blob::UUID)
 end
 function load_local{T}(coll::BlobCollection, blob::Blob{T})
     if !haskey(coll.cache, blob.id)
-        val = blob.data.value
-        (val == nothing) && (val = load(blob.metadata, coll.reader))
+        val = load(blob.metadata, coll.reader)
         blob.data.value = coll.cache[blob.id] = val
         blob.locality = locality(coll.reader, coll.nodemap)
     end
@@ -328,12 +327,9 @@ load(coll::BlobCollection, blobid::UUID) = load(coll, coll.blobs[blobid])
 load{T,L<:WeakLocality}(coll::BlobCollection, blob::Blob{T,L}) = load_local(coll, blob)
 function load{T,L<:StrongLocality}(coll::BlobCollection, blob::Blob{T,L})
     if !haskey(coll.cache, blob.id)
-        val = blob.data.value
-        if val == nothing
-            # select a node from blob's local nodes
-            fetchfrom = select_local(coll, blob)
-            val = (fetchfrom == myid()) ? load_local(coll.id, blob.id) : remotecall_fetch(load_local, fetchfrom, coll.id, blob.id)
-        end
+        # select a node from blob's local nodes
+        fetchfrom = select_local(coll, blob)
+        val = (fetchfrom == myid()) ? load_local(coll.id, blob.id) : remotecall_fetch(load_local, fetchfrom, coll.id, blob.id)
         blob.data.value = coll.cache[blob.id] = val
     end
     (coll.cache[blob.id])::T

src/cache/blobcache.jl

@@ -93,7 +93,7 @@ function Base.setindex!{K, V}(lru::LRU{K, V}, v, key)
     end
 
     while lru.isfull(lru)
-        rm = pop!(lru.q)
+        rm = last(lru.q)
         delete!(lru, rm.k)
     end
 
@@ -104,7 +104,7 @@ function Base.resize!(lru::LRU, n::Int)
     n < 0 && error("size must be a positive integer")
     lru.maxsize = n
     while lru.isfull(lru)
-        rm = pop!(lru.q)
+        rm = last(lru.q)
         delete!(lru, rm.k)
     end
     return lru