Add GC.logging_enabled() (#51647)

Author: fingolfin

NEWS.md

@@ -74,6 +74,7 @@ New library functions
 * `eachrsplit(string, pattern)` iterates split substrings right to left.
 * `Sys.username()` can be used to return the current user's username ([#51897]).
 * `wrap(Array, m::Union{MemoryRef{T}, Memory{T}}, dims)` which is the safe counterpart to `unsafe_wrap` ([#52049]).
+* `GC.logging_enabled()` can be used to test whether GC logging has been enabled via `GC.enable_logging` ([#51647]).
 
 New library features
 --------------------

base/gcutils.jl

@@ -262,4 +262,13 @@ function enable_logging(on::Bool=true)
     ccall(:jl_enable_gc_logging, Cvoid, (Cint,), on)
 end
 
+"""
+    GC.logging_enabled()
+
+Return whether GC logging has been enabled via [`GC.enable_logging`](@ref).
+"""
+function logging_enabled()
+    ccall(:jl_is_gc_logging_enabled, Cint, ()) != 0
+end
+
 end # module GC

doc/src/base/base.md

@@ -491,6 +491,7 @@ Base.GC.enable
 Base.GC.@preserve
 Base.GC.safepoint
 Base.GC.enable_logging
+Base.GC.logging_enabled
 Meta.lower
 Meta.@lower
 Meta.parse(::AbstractString, ::Int)

src/gc-debug.c

@@ -1207,6 +1207,10 @@ JL_DLLEXPORT void jl_enable_gc_logging(int enable) {
     gc_logging_enabled = enable;
 }
 
+JL_DLLEXPORT int jl_is_gc_logging_enabled(void) {
+    return gc_logging_enabled;
+}
+
 void _report_gc_finished(uint64_t pause, uint64_t freed, int full, int recollect, int64_t live_bytes) JL_NOTSAFEPOINT {
     if (!gc_logging_enabled) {
         return;

src/gc.h

@@ -726,6 +726,7 @@ void gc_count_pool(void);
 size_t jl_genericmemory_nbytes(jl_genericmemory_t *a) JL_NOTSAFEPOINT;
 
 JL_DLLEXPORT void jl_enable_gc_logging(int enable);
+JL_DLLEXPORT int jl_is_gc_logging_enabled(void);
 JL_DLLEXPORT uint32_t jl_get_num_stack_mappings(void);
 void _report_gc_finished(uint64_t pause, uint64_t freed, int full, int recollect, int64_t live_bytes) JL_NOTSAFEPOINT;
 

test/misc.jl

@@ -1343,8 +1343,10 @@ end
         open(tmppath, "w") do tmpio
             redirect_stderr(tmpio) do
                 GC.enable_logging(true)
+                @test GC.logging_enabled()
                 GC.gc()
                 GC.enable_logging(false)
+                @test !GC.logging_enabled()
             end
         end
         @test occursin("GC: pause", read(tmppath, String))