Add a CRYPTO_atomic_read call which allows an int variable to be read

in an atomic fashion.

Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/4414)

3 files changed, 31 insertions, 0 deletions

diff --git a/crypto/threads_none.c b/crypto/threads_none.c
index ffad7576b1..7e9ec2d151 100644
--- a/crypto/threads_none.c
+++ b/crypto/threads_none.c
@@ -125,6 +125,12 @@ int CRYPTO_atomic_add(int *val, int amount, int *ret, CRYPTO_RWLOCK *lock)
     return 1;
 }
 
+int CRYPTO_atomic_read(int *val, int *ret, CRYPTO_RWLOCK *lock)
+{
+    *ret  = *val;
+    return 1;
+}
+
 int openssl_init_fork_handlers(void)
 {
     return 0;
diff --git a/crypto/threads_pthread.c b/crypto/threads_pthread.c
index 9644c25aea..3f8ada2c37 100644
--- a/crypto/threads_pthread.c
+++ b/crypto/threads_pthread.c
@@ -169,6 +169,25 @@ int CRYPTO_atomic_add(int *val, int amount, int *ret, CRYPTO_RWLOCK *lock)
     return 1;
 }
 
+int CRYPTO_atomic_read(int *val, int *ret, CRYPTO_RWLOCK *lock)
+{
+# if defined(__GNUC__) && defined(__ATOMIC_ACQUIRE)
+    if (__atomic_is_lock_free(sizeof(*val), val)) {
+        __atomic_load(val, ret, __ATOMIC_ACQUIRE);
+        return 1;
+    }
+# endif
+    if (!CRYPTO_THREAD_write_lock(lock))
+        return 0;
+
+    *ret  = *val;
+
+    if (!CRYPTO_THREAD_unlock(lock))
+        return 0;
+
+    return 1;
+}
+
 # ifdef OPENSSL_SYS_UNIX
 static pthread_once_t fork_once_control = PTHREAD_ONCE_INIT;
 
diff --git a/crypto/threads_win.c b/crypto/threads_win.c
index 512e19f5f3..6f9c7b1bd3 100644
--- a/crypto/threads_win.c
+++ b/crypto/threads_win.c
@@ -133,6 +133,12 @@ int CRYPTO_atomic_add(int *val, int amount, int *ret, CRYPTO_RWLOCK *lock)
     return 1;
 }
 
+int CRYPTO_atomic_read(int *val, int *ret, CRYPTO_RWLOCK *lock)
+{
+    InterlockedCompareExchange(val, 0, 0);
+    return 1;
+}
+
 int openssl_init_fork_handlers(void)
 {
     return 0;