Make refcounts atomic for threading (dependent on appropriate

arch-dependent and compiler-dependent definitions in atomic.h
or else falls back to a global mutex to protect refcounts).

p4raw-id: //depot/perl@598

5 files changed, 129 insertions, 4 deletions

diff --git a/atomic.h b/atomic.h
new file mode 100644
index 0000000000..714bf23a6a
--- /dev/null
+++ b/atomic.h
@@ -0,0 +1,85 @@
+#ifdef __GNUC__
+
+/*
+ * These atomic operations copied from the linux kernel and altered
+ * only slightly. I need to get official permission to distribute
+ * under the Artistic License.
+ */
+/* We really need to integrate the atomic typedef with the typedef
+ * used by sv_refcnt of an SV. It's possible that for CPUs like alpha
+ * where we'd need to up sv_refcnt from 32 to 64 bits, we may be better
+ * off sticking with EMULATE_ATOMIC_REFCOUNTS instead.
+ */
+typedef U32 atomic_t;	/* kludge */
+
+#ifdef i386
+
+#  ifdef NO_SMP
+#    define LOCK ""
+#  else
+#    define LOCK "lock ; "
+#  endif
+
+#  define __atomic_fool_gcc(x) (*(struct { int a[100]; } *)x)
+static __inline__ void atomic_inc(atomic_t *v)
+{
+    __asm__ __volatile__(
+	    LOCK "incl %0"
+	    :"=m" (__atomic_fool_gcc(v))
+	    :"m" (__atomic_fool_gcc(v)));
+}
+
+static __inline__ int atomic_dec_and_test(atomic_t *v)
+{
+    unsigned char c;
+
+    __asm__ __volatile__(
+	    LOCK "decl %0; sete %1"
+	    :"=m" (__atomic_fool_gcc(v)), "=qm" (c)
+	    :"m" (__atomic_fool_gcc(v)));
+    return c != 0;
+}
+#  else
+/* XXX What symbol does gcc define for sparc64? */
+#  ifdef sparc64
+#    define __atomic_fool_gcc(x) ((struct { int a[100]; } *)x)
+typedef U32 atomic_t;
+extern __inline__ void atomic_add(int i, atomic_t *v)
+{
+        __asm__ __volatile__("
+1:      lduw            [%1], %%g5
+        add             %%g5, %0, %%g7
+        cas             [%1], %%g5, %%g7
+        sub             %%g5, %%g7, %%g5
+        brnz,pn         %%g5, 1b
+         nop"
+        : /* No outputs */
+        : "HIr" (i), "r" (__atomic_fool_gcc(v))
+        : "g5", "g7", "memory");
+}
+
+extern __inline__ int atomic_sub_return(int i, atomic_t *v)
+{
+        unsigned long oldval;
+        __asm__ __volatile__("
+1:      lduw            [%2], %%g5
+        sub             %%g5, %1, %%g7
+        cas             [%2], %%g5, %%g7
+        sub             %%g5, %%g7, %%g5
+        brnz,pn         %%g5, 1b
+         sub            %%g7, %1, %0"
+        : "=&r" (oldval)
+        : "HIr" (i), "r" (__atomic_fool_gcc(v))
+        : "g5", "g7", "memory");
+        return (int)oldval;
+}
+
+#define atomic_inc(v) atomic_add(1,(v))
+#define atomic_dec_and_test(v) (atomic_sub_return(1, (v)) == 0)
+/* Add further gcc architectures here */
+#  endif /* sparc64 */
+#endif /* i386 */
+#else
+/* Add non-gcc native atomic operations here */
+#  define EMULATE_ATOMIC_REFCOUNTS
+#endif
diff --git a/perl.c b/perl.c
index 0c525579af..6d222cecae 100644
--- a/perl.c
+++ b/perl.c
@@ -130,6 +130,9 @@ perl_construct(register PerlInterpreter *sv_interp)
 	COND_INIT(&eval_cond);
 	MUTEX_INIT(&threads_mutex);
 	COND_INIT(&nthreads_cond);
+#ifdef EMULATE_ATOMIC_REFCOUNTS
+	MUTEX_INIT(&svref_mutex);
+#endif /* EMULATE_ATOMIC_REFCOUNTS */
 	
 	thr = init_main_thread();
 #endif /* USE_THREADS */
diff --git a/perlvars.h b/perlvars.h
index 8a72312e57..69206a5d7a 100644
--- a/perlvars.h
+++ b/perlvars.h
@@ -19,6 +19,7 @@ PERLVAR(Geval_owner,	struct perl_thread *)		/* Owner thread for doeval */
 PERLVAR(Gnthreads,	int)		/* Number of threads currently */
 PERLVAR(Gthreads_mutex,	perl_mutex)		/* Mutex for nthreads and thread list */
 PERLVAR(Gnthreads_cond,	perl_cond)		/* Condition variable for nthreads */
+PERLVAR(Gsvref_mutex,	perl_mutex)		/* Mutex for SvREFCNT_{inc,dec} */
 PERLVARI(Gthreadsv_names,	char *,	THREADSV_NAMES)	
 #ifdef FAKE_THREADS
 PERLVAR(Gcurthr,	struct perl_thread *)	/* Currently executing (fake) thread */
diff --git a/sv.c b/sv.c
index 0edfdb2453..af74e28e0c 100644
--- a/sv.c
+++ b/sv.c
@@ -2870,13 +2870,15 @@ SV *
 sv_newref(SV *sv)
 {
     if (sv)
-	SvREFCNT(sv)++;
+	ATOMIC_INC(SvREFCNT(sv));
     return sv;
 }
 
 void
 sv_free(SV *sv)
 {
+    int refcount_is_zero;
+
     if (!sv)
 	return;
     if (SvREADONLY(sv)) {
@@ -2891,7 +2893,8 @@ sv_free(SV *sv)
 	warn("Attempt to free unreferenced scalar");
 	return;
     }
-    if (--SvREFCNT(sv) > 0)
+    ATOMIC_DEC_AND_TEST(refcount_is_zero, SvREFCNT(sv));
+    if (!refcount_is_zero)
 	return;
 #ifdef DEBUGGING
     if (SvTEMP(sv)) {
diff --git a/sv.h b/sv.h
index 5993a8de9b..bf3454765d 100644
--- a/sv.h
+++ b/sv.h
@@ -72,13 +72,46 @@ struct io {
 #define SvFLAGS(sv)	(sv)->sv_flags
 #define SvREFCNT(sv)	(sv)->sv_refcnt
 
+#ifdef USE_THREADS
+
+#  ifndef EMULATE_ATOMIC_REFCOUNTS
+#    include "atomic.h"
+#  endif
+
+#  ifdef EMULATE_ATOMIC_REFCOUNTS
+#    define ATOMIC_INC(count) STMT_START {	\
+	MUTEX_LOCK(&svref_mutex);		\
+	++count;				\
+	MUTEX_UNLOCK(&svref_mutex);		\
+     } STMT_END
+#    define ATOMIC_DEC_AND_TEST(res,count) 	\
+	MUTEX_LOCK(&svref_mutex);		\
+	res = (--count == 0);			\
+	MUTEX_UNLOCK(&svref_mutex);		\
+     } STMT_END
+#  else
+#    define ATOMIC_INC(count) atomic_inc(&count)
+#    define ATOMIC_DEC_AND_TEST(res,count) (res = atomic_dec_and_test(&count))
+#  endif /* EMULATE_ATOMIC_REFCOUNTS */
+#else
+#  define ATOMIC_INC(count) (++count)
+#  define ATOMIC_DEC_AND_TEST(res, count) (res = --count)
+#endif /* USE_THREADS */
+
 #ifdef __GNUC__
-#  define SvREFCNT_inc(sv) ({SV* nsv=(SV*)(sv); if(nsv) ++SvREFCNT(nsv); nsv;})
+#  define SvREFCNT_inc(sv)		\
+    ({					\
+	SV *nsv = (SV*)(sv);		\
+	if (nsv)			\
+	     ATOMIC_INC(SvREFCNT(nsv));	\
+	nsv;				\
+    })
 #else
 #  if defined(CRIPPLED_CC) || defined(USE_THREADS)
 #    define SvREFCNT_inc(sv) sv_newref((SV*)sv)
 #  else
-#    define SvREFCNT_inc(sv) ((Sv=(SV*)(sv)), (Sv && ++SvREFCNT(Sv)), (SV*)Sv)
+#    define SvREFCNT_inc(sv)	\
+	((Sv=(SV*)(sv)), (Sv && ATOMIC_INC(SvREFCNT(Sv))), (SV*)Sv)
 #  endif
 #endif