support BOOST_URL_DISABLE_THREADS

fix boostorg#684

.drone.star

@@ -25,7 +25,13 @@ def main(ctx):
          'freebsd-clang latest',
          'x86-msvc latest'],
         # Standards
-        '>=11')
+        '>=11') + [
+               linux_cxx("GCC 12 (no-mutex)", "g++-12", packages="g++-12", buildscript="drone", buildtype="boost",
+                         image="cppalliance/droneubuntu2204:1",
+                         environment={'B2_TOOLSET': 'gcc-12', 'B2_DEFINES': 'BOOST_URL_DISABLE_THREADS=1',
+                                      'B2_CXXSTD': '17'}, globalenv={'B2_CI_VERSION': '1', 'B2_VARIANT': 'release'}),
+           ]
+
 
 # from https://github.com/boostorg/boost-ci
 load("@boost_ci//ci/drone/:functions.star", "linux_cxx", "windows_cxx", "osx_cxx", "freebsd_cxx")
@@ -418,6 +424,7 @@ def generate(compiler_ranges, cxx_range, max_cxx=2, coverage=True, docs=True, as
 
     return jobs
 
+
 # Returns whether the specified compiler/version support a given standard
 # Ex: Checking if GCC 14 supports C++11
 # - compiler_supports('gcc', '14', '11') -> True
@@ -447,6 +454,7 @@ def compiler_supports(compiler, version, cxx):
             (cxx == '03' or cxx == '98')
     return False
 
+
 # Get list of available compiler versions in a semver range
 # - compilers_in_range('gcc >=10') -> [('gcc', '12'), ('gcc', '11'), ('gcc', '10')]
 def compilers_in_range(compiler_range_str):
@@ -480,6 +488,7 @@ def compilers_in_range(compiler_range_str):
             compilers.append((name, supported_version_str))
     return compilers
 
+
 # Get the C++ standard versions in a range of versions
 # Each C++ standard version can be represented by the two or
 # four char year version.
@@ -507,6 +516,7 @@ def cxxs_in_range(ranges):
             cxxs.append(str(v)[-2:])
     return cxxs
 
+
 # Check if a semver range contains a version
 # Each parameter can be a string or a version or range that has already been parsed.
 # - version_match('1.2.4', '>1.2.3') -> True
@@ -560,6 +570,7 @@ def version_match(v, ranges):
             break
     return any_in_disjunction
 
+
 # Parse a semver range
 # A semver range contains one or more semver comparators.
 # Each comparator can have one of the following operators:
@@ -623,6 +634,7 @@ def parse_semver_range(range_strs):
                     ranges[-1].append(['<', major + 1, 0, 0])
     return ranges
 
+
 # Parse a semver string
 # Ex:
 # - parse_semver('1.2.3') -> [1, 2, 3]

include/boost/url/grammar/detail/impl/recycled.ipp

@@ -11,8 +11,9 @@
 #define BOOST_URL_GRAMMAR_DETAIL_IMPL_RECYCLED_IPP
 
 #include <cstdlib>
-#include <mutex>
 #include <utility>
+#include <atomic>
+
 #ifdef BOOST_URL_REPORT
 # ifdef _MSC_VER
 #  include <intrin.h>
@@ -26,22 +27,20 @@ namespace detail {
 
 struct all_reports
 {
-    std::mutex m;
-
     // current count
-    std::size_t count = 0;
+    std::atomic<std::size_t> count = {0};
 
     // current bytes
-    std::size_t bytes = 0;
+    std::atomic<std::size_t> bytes = {0};
 
     // highest total ptr count
-    std::size_t count_max = 0;
+    std::atomic<std::size_t> count_max = {0};
 
     // highest total bytes
-    std::size_t bytes_max = 0;
+    std::atomic<std::size_t> bytes_max = {0};
 
     // largest single allocation
-    std::size_t alloc_max = 0;
+    std::atomic<std::size_t> alloc_max = {0};
 
     ~all_reports()
     {
@@ -61,30 +60,36 @@ void
 recycled_add_impl(
     std::size_t n) noexcept
 {
-    std::lock_guard<
-        std::mutex> m(all_reports_.m);
-
     auto& a = all_reports_;
 
-    a.count++;
-    if( a.count_max < a.count)
-        a.count_max = a.count;
-
-    a.bytes += n;
-    if( a.bytes_max < a.bytes)
-        a.bytes_max = a.bytes;
-
-    if( a.alloc_max < n)
-        a.alloc_max = n;
+    std::size_t new_count = ++a.count;
+    std::size_t old_count_max = a.count_max;
+    while (
+        old_count_max < new_count &&
+        !a.count_max.compare_exchange_weak(
+            old_count_max, new_count))
+    {}
+
+    std::size_t new_bytes = a.bytes.fetch_add(n);
+    std::size_t old_bytes_max = a.bytes_max;
+    while (
+        old_bytes_max < new_bytes &&
+        !a.bytes_max.compare_exchange_weak(
+            old_bytes_max, new_bytes))
+    {}
+
+    std::size_t old_alloc_max = a.alloc_max;
+    while (
+        old_alloc_max < n &&
+        !a.alloc_max.compare_exchange_weak(
+            old_alloc_max, n))
+    {}
 }
 
 void
 recycled_remove_impl(
     std::size_t n) noexcept
 {
-    std::lock_guard<
-        std::mutex> m(all_reports_.m);
-
     all_reports_.count--;
     all_reports_.bytes-=n;
 }

include/boost/url/grammar/detail/recycled.hpp

@@ -10,7 +10,6 @@
 #ifndef BOOST_URL_GRAMMAR_DETAIL_RECYCLED_HPP
 #define BOOST_URL_GRAMMAR_DETAIL_RECYCLED_HPP
 
-#include <mutex>
 #include <utility>
 
 namespace boost {

include/boost/url/grammar/impl/recycled.hpp

@@ -48,8 +48,10 @@ acquire() ->
 {
     U* p;
     {
+#if !defined(BOOST_URL_DISABLE_THREADS)
         std::lock_guard<
             std::mutex> lock(m_);
+#endif
         p = head_;
         if(p)
         {
@@ -75,10 +77,14 @@ release(U* u) noexcept
 {
     if(--u->refs != 0)
         return;
-    m_.lock();
-    u->next = head_;
-    head_ = u;
-    m_.unlock();
+    {
+#if !defined(BOOST_URL_DISABLE_THREADS)
+        std::lock_guard<
+            std::mutex> lock(m_);
+#endif
+        u->next = head_;
+        head_ = u;
+    }
     detail::recycled_add(
         sizeof(U));
 }

include/boost/url/grammar/recycled.hpp

@@ -17,6 +17,10 @@
 #include <type_traits>
 #include <stddef.h> // ::max_align_t
 
+#if !defined(BOOST_URL_DISABLE_THREADS)
+# include <mutex>
+#endif
+
 namespace boost {
 namespace urls {
 namespace grammar {
@@ -90,8 +94,14 @@ class recycled
     {
         T t;
         U* next = nullptr;
+
+#if !defined(BOOST_URL_DISABLE_THREADS)
         std::atomic<
             std::size_t> refs;
+#else
+        std::size_t refs;
+#endif
+
 
         U()
             : refs{1}
@@ -105,7 +115,10 @@ class recycled
     void release(U* u) noexcept;
 
     U* head_ = nullptr;
+
+#if !defined(BOOST_URL_DISABLE_THREADS)
     std::mutex m_;
+#endif
 };
 
 //------------------------------------------------