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Simplify the GC.gc interface. (JuliaLang#34303)
(cherry picked from commit b0ed147)
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‎base/gcutils.jl‎

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# This file is a part of Julia. License is MIT: https://julialang.org/license
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==(w::WeakRef, v::WeakRef) = isequal(w.value, v.value)
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==(w::WeakRef, v) = isequal(w.value, v)
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==(w, v::WeakRef) = isequal(w, v.value)
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"""
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finalizer(f, x)
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Register a function `f(x)` to be called when there are no program-accessible references to
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`x`, and return `x`. The type of `x` must be a `mutable struct`, otherwise the behavior of
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this function is unpredictable.
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`f` must not cause a task switch, which excludes most I/O operations such as `println`.
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Using the `@async` macro (to defer context switching to outside of the finalizer) or
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`ccall` to directly invoke IO functions in C may be helpful for debugging purposes.
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# Examples
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```julia
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finalizer(my_mutable_struct) do x
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@async println("Finalizing \$x.")
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end
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finalizer(my_mutable_struct) do x
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ccall(:jl_safe_printf, Cvoid, (Cstring, Cstring), "Finalizing %s.", repr(x))
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end
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```
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"""
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function finalizer(@nospecialize(f), @nospecialize(o))
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if !ismutable(o)
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error("objects of type ", typeof(o), " cannot be finalized")
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end
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ccall(:jl_gc_add_finalizer_th, Cvoid, (Ptr{Cvoid}, Any, Any),
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Core.getptls(), o, f)
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return o
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end
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function finalizer(f::Ptr{Cvoid}, o::T) where T
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@_inline_meta
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if !ismutable(o)
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error("objects of type ", typeof(o), " cannot be finalized")
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end
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ccall(:jl_gc_add_ptr_finalizer, Cvoid, (Ptr{Cvoid}, Any, Ptr{Cvoid}),
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Core.getptls(), o, f)
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return o
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end
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"""
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finalize(x)
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Immediately run finalizers registered for object `x`.
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"""
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finalize(@nospecialize(o)) = ccall(:jl_finalize_th, Cvoid, (Ptr{Cvoid}, Any,),
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Core.getptls(), o)
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"""
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Base.GC
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Module with garbage collection utilities.
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"""
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module GC
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# mirrored from julia.h
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const GC_AUTO = 0
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const GC_FULL = 1
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const GC_INCREMENTAL = 2
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"""
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GC.gc([full=true])
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Perform garbage collection. The argument `full` determines the kind of
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collection: A full collection (default) sweeps all objects, which makes the
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next GC scan much slower, while an incremental collection may only sweep
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so-called young objects.
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!!! warning
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Excessive use will likely lead to poor performance.
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"""
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gc(full::Bool=true) =
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ccall(:jl_gc_collect, Cvoid, (Cint,), full ? GC_FULL : GC_INCREMENTAL)
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"""
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GC.enable(on::Bool)
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Control whether garbage collection is enabled using a boolean argument (`true` for enabled,
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`false` for disabled). Return previous GC state.
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!!! warning
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Disabling garbage collection should be used only with caution, as it can cause memory
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use to grow without bound.
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"""
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enable(on::Bool) = ccall(:jl_gc_enable, Int32, (Int32,), on) != 0
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"""
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GC.@preserve x1 x2 ... xn expr
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Mark the objects `x1, x2, ...` as being *in use* during the evaluation of the
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expression `expr`. This is only required in unsafe code where `expr`
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*implicitly uses* memory or other resources owned by one of the `x`s.
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*Implicit use* of `x` covers any indirect use of resources logically owned by
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`x` which the compiler cannot see. Some examples:
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* Accessing memory of an object directly via a `Ptr`
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* Passing a pointer to `x` to `ccall`
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* Using resources of `x` which would be cleaned up in the finalizer.
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`@preserve` should generally not have any performance impact in typical use
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cases where it briefly extends object lifetime. In implementation, `@preserve`
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has effects such as protecting dynamically allocated objects from garbage
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collection.
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# Examples
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When loading from a pointer with `unsafe_load`, the underlying object is
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implicitly used, for example `x` is implicitly used by `unsafe_load(p)` in the
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following:
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```jldoctest
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julia> let
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x = Ref{Int}(101)
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p = Base.unsafe_convert(Ptr{Int}, x)
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GC.@preserve x unsafe_load(p)
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end
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101
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```
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When passing pointers to `ccall`, the pointed-to object is implicitly used and
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should be preserved. (Note however that you should normally just pass `x`
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directly to `ccall` which counts as an explicit use.)
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```jldoctest
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julia> let
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x = "Hello"
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p = pointer(x)
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GC.@preserve x @ccall strlen(p::Cstring)::Cint
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# Preferred alternative
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@ccall strlen(x::Cstring)::Cint
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end
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5
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```
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"""
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macro preserve(args...)
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syms = args[1:end-1]
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for x in syms
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isa(x, Symbol) || error("Preserved variable must be a symbol")
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end
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esc(Expr(:gc_preserve, args[end], syms...))
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end
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"""
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GC.safepoint()
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Inserts a point in the program where garbage collection may run.
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This can be useful in rare cases in multi-threaded programs where some threads
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are allocating memory (and hence may need to run GC) but other threads are doing
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only simple operations (no allocation, task switches, or I/O).
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Calling this function periodically in non-allocating threads allows garbage
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collection to run.
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!!! compat "Julia 1.4"
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This function is available as of Julia 1.4.
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"""
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safepoint() = ccall(:jl_gc_safepoint, Cvoid, ())
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end # module GC
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# This file is a part of Julia. License is MIT: https://julialang.org/license
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==(w::WeakRef, v::WeakRef) = isequal(w.value, v.value)
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==(w::WeakRef, v) = isequal(w.value, v)
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==(w, v::WeakRef) = isequal(w, v.value)
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"""
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finalizer(f, x)
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Register a function `f(x)` to be called when there are no program-accessible references to
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`x`, and return `x`. The type of `x` must be a `mutable struct`, otherwise the behavior of
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this function is unpredictable.
13+
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`f` must not cause a task switch, which excludes most I/O operations such as `println`.
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Using the `@async` macro (to defer context switching to outside of the finalizer) or
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`ccall` to directly invoke IO functions in C may be helpful for debugging purposes.
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# Examples
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```julia
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finalizer(my_mutable_struct) do x
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@async println("Finalizing \$x.")
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end
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finalizer(my_mutable_struct) do x
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ccall(:jl_safe_printf, Cvoid, (Cstring, Cstring), "Finalizing %s.", repr(x))
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end
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```
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"""
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function finalizer(@nospecialize(f), @nospecialize(o))
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if !ismutable(o)
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error("objects of type ", typeof(o), " cannot be finalized")
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end
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ccall(:jl_gc_add_finalizer_th, Cvoid, (Ptr{Cvoid}, Any, Any),
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Core.getptls(), o, f)
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return o
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end
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function finalizer(f::Ptr{Cvoid}, o::T) where T
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@_inline_meta
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if !ismutable(o)
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error("objects of type ", typeof(o), " cannot be finalized")
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end
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ccall(:jl_gc_add_ptr_finalizer, Cvoid, (Ptr{Cvoid}, Any, Ptr{Cvoid}),
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Core.getptls(), o, f)
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return o
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end
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"""
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finalize(x)
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Immediately run finalizers registered for object `x`.
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"""
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finalize(@nospecialize(o)) = ccall(:jl_finalize_th, Cvoid, (Ptr{Cvoid}, Any,),
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Core.getptls(), o)
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"""
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Base.GC
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Module with garbage collection utilities.
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"""
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module GC
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# mirrored from julia.h
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const GC_AUTO = 0
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const GC_FULL = 1
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const GC_INCREMENTAL = 2
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"""
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GC.gc([full=true])
70+
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Perform garbage collection. The argument `full` determines the kind of
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collection: A full collection (default) sweeps all objects, which makes the
73+
next GC scan much slower, while an incremental collection may only sweep
74+
so-called young objects.
75+
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!!! warning
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Excessive use will likely lead to poor performance.
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"""
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gc(full::Bool=true) =
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ccall(:jl_gc_collect, Cvoid, (Cint,), full ? GC_FULL : GC_INCREMENTAL)
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"""
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GC.enable(on::Bool)
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Control whether garbage collection is enabled using a boolean argument (`true` for enabled,
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`false` for disabled). Return previous GC state.
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!!! warning
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Disabling garbage collection should be used only with caution, as it can cause memory
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use to grow without bound.
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"""
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enable(on::Bool) = ccall(:jl_gc_enable, Int32, (Int32,), on) != 0
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"""
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GC.@preserve x1 x2 ... xn expr
96+
97+
Mark the objects `x1, x2, ...` as being *in use* during the evaluation of the
98+
expression `expr`. This is only required in unsafe code where `expr`
99+
*implicitly uses* memory or other resources owned by one of the `x`s.
100+
101+
*Implicit use* of `x` covers any indirect use of resources logically owned by
102+
`x` which the compiler cannot see. Some examples:
103+
* Accessing memory of an object directly via a `Ptr`
104+
* Passing a pointer to `x` to `ccall`
105+
* Using resources of `x` which would be cleaned up in the finalizer.
106+
107+
`@preserve` should generally not have any performance impact in typical use
108+
cases where it briefly extends object lifetime. In implementation, `@preserve`
109+
has effects such as protecting dynamically allocated objects from garbage
110+
collection.
111+
112+
# Examples
113+
114+
When loading from a pointer with `unsafe_load`, the underlying object is
115+
implicitly used, for example `x` is implicitly used by `unsafe_load(p)` in the
116+
following:
117+
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```jldoctest
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julia> let
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x = Ref{Int}(101)
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p = Base.unsafe_convert(Ptr{Int}, x)
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GC.@preserve x unsafe_load(p)
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end
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101
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```
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When passing pointers to `ccall`, the pointed-to object is implicitly used and
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should be preserved. (Note however that you should normally just pass `x`
129+
directly to `ccall` which counts as an explicit use.)
130+
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```jldoctest
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julia> let
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x = "Hello"
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p = pointer(x)
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GC.@preserve x @ccall strlen(p::Cstring)::Cint
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# Preferred alternative
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@ccall strlen(x::Cstring)::Cint
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end
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5
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```
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"""
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macro preserve(args...)
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syms = args[1:end-1]
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for x in syms
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isa(x, Symbol) || error("Preserved variable must be a symbol")
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end
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esc(Expr(:gc_preserve, args[end], syms...))
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end
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"""
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GC.safepoint()
152+
153+
Inserts a point in the program where garbage collection may run.
154+
This can be useful in rare cases in multi-threaded programs where some threads
155+
are allocating memory (and hence may need to run GC) but other threads are doing
156+
only simple operations (no allocation, task switches, or I/O).
157+
Calling this function periodically in non-allocating threads allows garbage
158+
collection to run.
159+
160+
!!! compat "Julia 1.4"
161+
This function is available as of Julia 1.4.
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"""
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safepoint() = ccall(:jl_gc_safepoint, Cvoid, ())
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end # module GC

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