Rewrite ethread library

Large parts of the ethread library have been rewritten. The
ethread library is an Erlang runtime system internal, portable
thread library used by the runtime system itself.

Most notable improvement is a reader optimized rwlock
implementation which dramatically improve the performance of
read-lock/read-unlock operations on multi processor systems by
avoiding ping-ponging of the rwlock cache lines. The reader
optimized rwlock implementation is used by miscellaneous
rwlocks in the runtime system that are known to be read-locked
frequently, and can be enabled on ETS tables by passing the
`{read_concurrency, true}' option upon table creation. See the
documentation of `ets:new/2' for more information.

The ethread library can now also use the libatomic_ops library
for atomic memory accesses. This makes it possible for the
Erlang runtime system to utilize optimized atomic operations
on more platforms than before. Use the
`--with-libatomic_ops=PATH' configure command line argument
when specifying where the libatomic_ops installation is
located. The libatomic_ops library can be downloaded from:
http://www.hpl.hp.com/research/linux/atomic_ops/

The changed API of the ethread library has also caused
modifications in the Erlang runtime system. Preparations for
the to come "delayed deallocation" feature has also been done
since it depends on the ethread library.

Note: When building for x86, the ethread library will now use
instructions that first appeared on the pentium 4 processor. If
you want the runtime system to be compatible with older
processors (back to 486) you need to pass the
`--enable-ethread-pre-pentium4-compatibility' configure command
line argument when configuring the system.

1 files changed, 19 insertions, 0 deletions

diff --git a/erts/include/internal/gcc/ethr_atomic.h b/erts/include/internal/gcc/ethr_atomic.h
index 775030c8d5..5fe6e23477 100644
--- a/erts/include/internal/gcc/ethr_atomic.h
+++ b/erts/include/internal/gcc/ethr_atomic.h
@@ -55,6 +55,7 @@ do { \
     volatile long x___ = 0; \
     (void) __sync_val_compare_and_swap(&x___, (long) 0, (long) 1); \
 } while (0)
+#define ETHR_READ_DEPEND_MEMORY_BARRIER ETHR_MEMORY_BARRIER
 
 #if defined(ETHR_TRY_INLINE_FUNCS) || defined(ETHR_AUX_IMPL__)
 
@@ -157,6 +158,24 @@ ethr_native_atomic_xchg(ethr_native_atomic_t *var, long new)
     return act;
 }
 
+/*
+ * Atomic ops with at least specified barriers.
+ */
+
+static ETHR_INLINE long
+ethr_native_atomic_read_acqb(ethr_native_atomic_t *var)
+{
+    return __sync_add_and_fetch(&var->counter, (long) 0);
+}
+
+#define ethr_native_atomic_inc_return_acqb ethr_native_atomic_inc_return
+#define ethr_native_atomic_set_relb ethr_native_atomic_xchg
+#define ethr_native_atomic_dec_relb ethr_native_atomic_dec_return
+#define ethr_native_atomic_dec_return_relb ethr_native_atomic_dec_return
+
+#define ethr_native_atomic_cmpxchg_acqb ethr_native_atomic_cmpxchg
+#define ethr_native_atomic_cmpxchg_relb ethr_native_atomic_cmpxchg
+
 #endif
 
 #endif