From e67dac1d7493741cf88b411f68e31fc496179bf2 Mon Sep 17 00:00:00 2001 From: Qyriad Date: Mon, 15 Jul 2024 18:19:54 -0600 Subject: [PATCH] libexpr: rename confusing makeImmutableString -> gcCopyStringIfNeeded The purpose of this function has little to do with immutability. Value's strings are never mutated, and the point of this function is to singleton empty strings. Change-Id: Ifd41dd952409d54e4d3de9ab59064e6928b0e480 --- src/libexpr/eval.cc | 21 +++------------------ src/libexpr/gc-alloc.cc | 23 +++++++++++++++++++++++ src/libexpr/gc-alloc.hh | 5 +++++ src/libexpr/meson.build | 1 + 4 files changed, 32 insertions(+), 18 deletions(-) create mode 100644 src/libexpr/gc-alloc.cc diff --git a/src/libexpr/eval.cc b/src/libexpr/eval.cc index ce469e5c5..06b1f27f5 100644 --- a/src/libexpr/eval.cc +++ b/src/libexpr/eval.cc @@ -49,21 +49,6 @@ using json = nlohmann::json; namespace nix { -// When there's no need to write to the string, we can optimize away empty -// string allocations. -// This function handles makeImmutableString(std::string_view()) by returning -// the empty string. -static const char * makeImmutableString(std::string_view s) -{ - const size_t size = s.size(); - if (size == 0) - return ""; - auto t = gcAllocString(size + 1); - memcpy(t, s.data(), size); - t[size] = '\0'; - return t; -} - RootValue allocRootValue(Value * v) { #if HAVE_BOEHMGC @@ -784,7 +769,7 @@ DebugTraceStacker::DebugTraceStacker(EvalState & evalState, DebugTrace t) void Value::mkString(std::string_view s) { - mkString(makeImmutableString(s)); + mkString(gcCopyStringIfNeeded(s)); } @@ -795,7 +780,7 @@ static void copyContextToValue(Value & v, const NixStringContext & context) v.string.context = (const char * *) gcAllocBytes((context.size() + 1) * sizeof(char *)); for (auto & i : context) - v.string.context[n++] = makeImmutableString(i.to_string()); + v.string.context[n++] = gcCopyStringIfNeeded(i.to_string()); v.string.context[n] = 0; } } @@ -815,7 +800,7 @@ void Value::mkStringMove(const char * s, const NixStringContext & context) void Value::mkPath(const SourcePath & path) { - mkPath(makeImmutableString(path.path.abs())); + mkPath(gcCopyStringIfNeeded(path.path.abs())); } diff --git a/src/libexpr/gc-alloc.cc b/src/libexpr/gc-alloc.cc new file mode 100644 index 000000000..558a2f2bc --- /dev/null +++ b/src/libexpr/gc-alloc.cc @@ -0,0 +1,23 @@ +#include "gc-alloc.hh" + +#include +#include + +namespace nix +{ + +char const * gcCopyStringIfNeeded(std::string_view toCopyFrom) +{ + if (toCopyFrom.empty()) { + return ""; + } + + size_t const size = toCopyFrom.size(); + char * cstr = gcAllocString(size + 1); + memcpy(cstr, toCopyFrom.data(), size); + cstr[size] = '\0'; + + return cstr; +} + +} diff --git a/src/libexpr/gc-alloc.hh b/src/libexpr/gc-alloc.hh index a16bc65e4..f691bfc4b 100644 --- a/src/libexpr/gc-alloc.hh +++ b/src/libexpr/gc-alloc.hh @@ -7,6 +7,7 @@ #include #include #include +#include #include #if HAVE_BOEHMGC @@ -116,4 +117,8 @@ inline char * gcAllocString(size_t size) return cstr; } +/// Returns a C-string copied from @ref toCopyFrom, or a single, static empty +/// string if @ref toCopyFrom is also empty. +char const * gcCopyStringIfNeeded(std::string_view toCopyFrom); + } diff --git a/src/libexpr/meson.build b/src/libexpr/meson.build index d29359298..b11e4c2e0 100644 --- a/src/libexpr/meson.build +++ b/src/libexpr/meson.build @@ -22,6 +22,7 @@ libexpr_sources = files( 'eval.cc', 'function-trace.cc', 'get-drvs.cc', + 'gc-alloc.cc', 'json-to-value.cc', 'nixexpr.cc', 'parser/parser.cc',