[libcxx-commits] [PATCH] D126882: [libc++] Do not yield from __sp_mut::lock()

[Louis Dionne via Phabricator via libcxx-commits]

This revision was not accepted when it landed; it landed in state "Needs Review".
This revision was landed with ongoing or failed builds.
This revision was automatically updated to reflect the committed changes.
Closed by commit rG5b386ac912ea: [libc++] Do not yield from __sp_mut::lock() (authored by ldionne).

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D126882/new/

https://reviews.llvm.org/D126882

Files:
  libcxx/src/memory.cpp


Index: libcxx/src/memory.cpp
===================================================================
--- libcxx/src/memory.cpp
+++ libcxx/src/memory.cpp
@@ -138,9 +138,13 @@
 
 #if !defined(_LIBCPP_HAS_NO_THREADS)
 
-static constexpr std::size_t __sp_mut_count = 16;
+static constexpr std::size_t __sp_mut_count = 32;
 static constinit __libcpp_mutex_t mut_back[__sp_mut_count] =
 {
+    _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER,
+    _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER,
+    _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER,
+    _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER,
     _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER,
     _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER,
     _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER, _LIBCPP_MUTEX_INITIALIZER,
@@ -156,16 +160,7 @@
 __sp_mut::lock() noexcept
 {
     auto m = static_cast<__libcpp_mutex_t*>(__lx);
-    unsigned count = 0;
-    while (!__libcpp_mutex_trylock(m))
-    {
-        if (++count > 16)
-        {
-            __libcpp_mutex_lock(m);
-            break;
-        }
-        this_thread::yield();
-    }
+    __libcpp_mutex_lock(m);
 }
 
 void
@@ -181,7 +176,11 @@
         &mut_back[ 0], &mut_back[ 1], &mut_back[ 2], &mut_back[ 3],
         &mut_back[ 4], &mut_back[ 5], &mut_back[ 6], &mut_back[ 7],
         &mut_back[ 8], &mut_back[ 9], &mut_back[10], &mut_back[11],
-        &mut_back[12], &mut_back[13], &mut_back[14], &mut_back[15]
+        &mut_back[12], &mut_back[13], &mut_back[14], &mut_back[15],
+        &mut_back[16], &mut_back[17], &mut_back[18], &mut_back[19],
+        &mut_back[20], &mut_back[21], &mut_back[22], &mut_back[23],
+        &mut_back[24], &mut_back[25], &mut_back[26], &mut_back[27],
+        &mut_back[28], &mut_back[29], &mut_back[30], &mut_back[31]
     };
     return muts[hash<const void*>()(p) & (__sp_mut_count-1)];
 }


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