Lock-free ROOTFile.fobj

[Moelf]

there's a super free optimization that is especially effectively for network I/O:

First:

diff --git a/src/iteration.jl b/src/iteration.jl
index 04e5d7d..7e30835 100644
--- a/src/iteration.jl
+++ b/src/iteration.jl
@@ -333,7 +333,7 @@ function Base.getindex(ba::LazyBranch{T,J,B}, range::UnitRange) where {T,J,B}
     ib2 = findfirst(x -> x > (last(range) - 1), ba.fEntry) - 1
     offset = ba.fEntry[ib1]
     range = (first(range)-offset):(last(range)-offset)
-    return vcat([basketarray(ba, i) for i in ib1:ib2]...)[range]
+    return Vcat(asyncmap(i->basketarray(ba, i), ib1:ib2)...)[range]
 end

but to make this useful, we also need:

diff --git a/src/root.jl b/src/root.jl
index e4eb852..abb1c09 100644
--- a/src/root.jl
+++ b/src/root.jl
@@ -472,17 +472,17 @@ function readbasket(f::ROOTFile, branch, ith)
 end
 
 function readbasketseek(f::ROOTFile, branch::Union{TBranch, TBranchElement}, seek_pos::Int, nb)
-    lock(f)
-    local basketkey, compressedbytes
+    # lock(f)
+    local rawbuffer
     try
         seek(f.fobj, seek_pos)
         rawbuffer = OffsetBuffer(IOBuffer(read(f.fobj, nb)), seek_pos)
-        basketkey = unpack(rawbuffer, TBasketKey)
-        compressedbytes = compressed_datastream(rawbuffer, basketkey)
     catch
         finally
-        unlock(f)
+        # unlock(f)
     end
+    basketkey = unpack(rawbuffer, TBasketKey)
+    compressedbytes = compressed_datastream(rawbuffer, basketkey)

Now, the problem of course is that removing the lock will fuck up our multi-threaded reading, because the current cursor location is stored in IOStream. Technically, network based ones don't need a position() since each read is bytes range based, but our on-disk IOStream will surely complain.

1. One possibility is to use MMap based for on-disk files
2. or we can "duplicate" cursor object for each file for each thread...

[Moelf]

#150 attempted to add a MmapStream