minor cleanups to MemoryRef (JuliaLang#51937)

Author: vtjnash

base/abstractarray.jl

@@ -1034,6 +1034,8 @@ the other elements are left untouched.
 
 See also [`copy!`](@ref Base.copy!), [`copy`](@ref).
 
+$(_DOCS_ALIASING_WARNING)
+
 # Examples
 ```jldoctest
 julia> x = [1., 0., 3., 0., 5.];

base/array.jl

@@ -276,8 +276,6 @@ source and `do` in the destination (1-indexed).
 The `unsafe` prefix on this function indicates that no validation is performed to ensure
 that N is inbounds on either array. Incorrect usage may corrupt or segfault your program, in
 the same manner as C.
-
-$(_DOCS_ALIASING_WARNING)
 """
 function unsafe_copyto!(dest::Array, doffs, src::Array, soffs, n)
     n == 0 && return dest
@@ -291,24 +289,26 @@ end
 Copy `N` elements from collection `src` starting at the linear index `so`, to array `dest` starting at
 the index `do`. Return `dest`.
 """
-function copyto!(dest::Array, doffs::Integer, src::Array, soffs::Integer, n::Integer)
-    return _copyto_impl!(dest, doffs, src, soffs, n)
-end
+copyto!(dest::Array, doffs::Integer, src::Array, soffs::Integer, n::Integer) = _copyto_impl!(dest, doffs, src, soffs, n)
+copyto!(dest::Array, doffs::Integer, src::Memory, soffs::Integer, n::Integer) = _copyto_impl!(dest, doffs, src, soffs, n)
+copyto!(dest::Memory, doffs::Integer, src::Array, soffs::Integer, n::Integer) = _copyto_impl!(dest, doffs, src, soffs, n)
 
 # this is only needed to avoid possible ambiguities with methods added in some packages
-function copyto!(dest::Array{T}, doffs::Integer, src::Array{T}, soffs::Integer, n::Integer) where T
-    return _copyto_impl!(dest, doffs, src, soffs, n)
-end
+copyto!(dest::Array{T}, doffs::Integer, src::Array{T}, soffs::Integer, n::Integer) where {T} = _copyto_impl!(dest, doffs, src, soffs, n)
 
-function _copyto_impl!(dest::Array, doffs::Integer, src::Array, soffs::Integer, n::Integer)
+function _copyto_impl!(dest::Union{Array,Memory}, doffs::Integer, src::Union{Array,Memory}, soffs::Integer, n::Integer)
     n == 0 && return dest
     n > 0 || _throw_argerror("Number of elements to copy must be non-negative.")
     @boundscheck checkbounds(dest, doffs:doffs+n-1)
     @boundscheck checkbounds(src, soffs:soffs+n-1)
-    unsafe_copyto!(dest, doffs, src, soffs, n)
+    @inbounds let dest = GenericMemoryRef(dest isa Array ? getfield(dest, :ref) : dest, doffs)
+                  src = GenericMemoryRef(src isa Array ? getfield(src, :ref) : src, soffs)
+        unsafe_copyto!(dest, src, n)
+    end
     return dest
 end
 
+
 # Outlining this because otherwise a catastrophic inference slowdown
 # occurs, see discussion in #27874.
 # It is also mitigated by using a constant string.

base/genericmemory.jl

@@ -68,7 +68,7 @@ end
 @eval isassigned(a::GenericMemoryRef) = memoryref_isassigned(a, :not_atomic, $(Expr(:boundscheck)))
 
 ## copy ##
-@eval function unsafe_copyto!(dest::MemoryRef{T}, src::MemoryRef{T}, n) where {T}
+function unsafe_copyto!(dest::MemoryRef{T}, src::MemoryRef{T}, n) where {T}
     @_terminates_globally_meta
     n == 0 && return dest
     @boundscheck GenericMemoryRef(dest, n), GenericMemoryRef(src, n)
@@ -118,6 +118,13 @@ end
 
 copy(a::T) where {T<:Memory} = ccall(:jl_genericmemory_copy, Ref{T}, (Any,), a)
 
+function copyto!(dest::Memory, doffs::Integer, src::Memory, soffs::Integer, n::Integer)
+    n < 0 && _throw_argerror("Number of elements to copy must be non-negative.")
+    unsafe_copyto!(dest, doffs, src, soffs, n)
+    return dest
+end
+
+
 ## Constructors ##
 
 similar(a::Memory{T}) where {T}                   = Memory{T}(undef, length(a))

doc/src/manual/embedding.md

@@ -432,14 +432,14 @@ object has just been allocated and no garbage collection has run since then. Not
 `jl_...` functions can sometimes invoke garbage collection.
 
 The write barrier is also necessary for arrays of pointers when updating their data directly.
-For example:
+Calling `jl_array_ptr_set` is usually much preferred. But direct updates can be done. For example:
 
 ```c
 jl_array_t *some_array = ...; // e.g. a Vector{Any}
 void **data = jl_array_data(some_array, void*);
 jl_value_t *some_value = ...;
 data[0] = some_value;
-jl_gc_wb(some_array, some_value);
+jl_gc_wb(jl_array_owner(some_array), some_value);
 ```
 
 ### Controlling the Garbage Collector

stdlib/Base64/src/buffer.jl

@@ -2,37 +2,37 @@
 
 # Data buffer for pipes.
 mutable struct Buffer
-    data::Memory{UInt8}
-    ptr::Ptr{UInt8}
+    const data::Memory{UInt8}
+    offset::Int
     size::Int
 
     function Buffer(bufsize)
         data = Memory{UInt8}(undef, bufsize)
-        return new(data, pointer(data), 0)
+        return new(data, 0, 0)
     end
 end
 
 Base.empty!(buffer::Buffer) = buffer.size = 0
-Base.getindex(buffer::Buffer, i::Integer) = unsafe_load(buffer.ptr, i)
-Base.setindex!(buffer::Buffer, v::UInt8, i::Integer) = unsafe_store!(buffer.ptr, v, i)
+Base.getindex(buffer::Buffer, i::Integer) = buffer.data[buffer.offset + i]
+Base.setindex!(buffer::Buffer, v::UInt8, i::Integer) = buffer.data[buffer.offset + i] = v
 Base.firstindex(buffer::Buffer) = 1
 Base.lastindex(buffer::Buffer) = buffer.size
-Base.pointer(buffer::Buffer) = buffer.ptr
-capacity(buffer::Buffer) = Int(pointer(buffer.data, lastindex(buffer.data)) - buffer.ptr) + 1
+Base.pointer(buffer::Buffer) = pointer(buffer.data) + buffer.offset
+capacity(buffer::Buffer) = length(buffer.data) - buffer.offset
 
 function consumed!(buffer::Buffer, n::Integer)
     @assert n ≤ buffer.size
-    buffer.ptr += n
+    buffer.offset += n
     buffer.size -= n
 end
 
 function read_to_buffer(io::IO, buffer::Buffer)
-    offset = buffer.ptr - pointer(buffer.data)
+    offset = buffer.offset
     copyto!(buffer.data, 1, buffer.data, offset + 1, buffer.size)
-    buffer.ptr = pointer(buffer.data)
+    buffer.offset = 0
     if !eof(io)
         n = min(bytesavailable(io), capacity(buffer) - buffer.size)
-        unsafe_read(io, buffer.ptr + buffer.size, n)
+        unsafe_read(io, pointer(buffer) + buffer.size, n)
         buffer.size += n
     end
     return