core: Introduce atomic counters

- Move generic implementation of atomic_set_return to core/atomic.c
 - Generic implementation of atomic compare and swap in core/atomic.c
 - atomic_cas is used to implement atomic counters in core/include/atomic.h
 - atomic_int_t is an atomic integer type
 - ATOMIC_INIT can be used as an initializer for atomic_int_t
 - ATOMIC_VALUE gets a reference to the value of an atomic integer

core/atomic.c

@@ -0,0 +1,59 @@
+/*
+ * Copyright (C) 2014 Freie Universität Berlin
+ * Copyright (C) 2015 Eistec AB
+ *
+ * This file is subject to the terms and conditions of the GNU Lesser General
+ * Public License v2.1. See the file LICENSE in the top level directory for more
+ * details.
+ */
+
+
+/**
+ * @ingroup     core_util
+ * @{
+ *
+ * @file
+ * @brief       Generic implementation of the kernel's atomic interface
+ *
+ * @author      Kaspar Schleiser <kaspar@schleiser.de>
+ * @author      Oliver Hahm <oliver.hahm@inria.fr>
+ * @author      Joakim Gebart <joakim.gebart@eistec.se>
+ *
+ * @}
+ */
+
+#include "irq.h"
+#include "cpu.h"
+#include "atomic.h"
+
+#if (ARCH_HAS_ATOMIC_SET_RETURN == 0)
+
+unsigned int atomic_set_return(unsigned int *val, unsigned int set)
+{
+    unsigned int mask = disableIRQ();
+    unsigned int old_val = *val;
+    *val = set;
+    restoreIRQ(mask);
+    return old_val;
+}
+
+#endif
+
+/* Set ARCH_HAS_ATOMIC_COMPARE_AND_SWAP within cpu.h to override this function */
+#if (ARCH_HAS_ATOMIC_COMPARE_AND_SWAP == 0)
+
+int atomic_cas(atomic_int_t *var, int old, int now)
+{
+    unsigned int mask = disableIRQ();
+
+    if (ATOMIC_VALUE(*var) != old) {
+        restoreIRQ(mask);
+        return 0;
+    }
+
+    ATOMIC_VALUE(*var) = now;
+    restoreIRQ(mask);
+    return 1;
+}
+
+#endif

core/include/atomic.h

@@ -1,5 +1,6 @@
 /*
  * Copyright (C) 2014 Freie Universität Berlin
+ * Copyright (C) 2015 Eistec AB
  *
  * This file is subject to the terms and conditions of the GNU Lesser
  * General Public License v2.1. See the file LICENSE in the top level
@@ -10,21 +11,31 @@
  * @addtogroup  core_util
  * @{
  *
- * @file        atomic.h
- * @brief       Atomic getter and setter functions
+ * @file
+ * @brief       Functions for atomic handling of variables
  *
  * @author      Kaspar Schleiser <kaspar@schleiser.de>
+ * @author      Joakim Gebart <joakim.gebart@eistec.se>
  */
 
-#ifndef _ATOMIC_H
-#define _ATOMIC_H
+#ifndef ATOMIC_H_
+#define ATOMIC_H_
 
 #include "arch/atomic_arch.h"
 
 #ifdef __cplusplus
- extern "C" {
+extern "C" {
 #endif
 
+/**
+ * @brief Integer variable for use in atomic counters.
+ */
+typedef struct atomic_int {
+    volatile int value;
+} atomic_int_t;
+
+
+
 /**
  * @brief Sets a new and returns the old value of a variable atomically
  *
@@ -35,9 +46,119 @@
  */
 unsigned int atomic_set_return(unsigned int *val, unsigned int set);
 
+/**
+ * @brief Initializer for atomic variables
+ *
+ * @param[in] val  initial value for the atomic integer
+ */
+#define ATOMIC_INIT(val) {(val)}
+
+/**
+ * @brief Atomic Compare and Swap
+ *
+ * Updates the value in var iff the current value of var is equal to old.
+ *
+ * @param[inout] var  Atomic variable to update
+ * @param[in]    old  The old value to compare against
+ * @param[in]    now  The new value to write to var
+ *
+ * @return 1 if the write completed successfully
+ * @return 0 if the write failed.
+ */
+int atomic_cas(atomic_int_t *var, int old, int now);
+
+/**
+ * @brief Increment a counter variable by one atomically and return the old value.
+ *
+ * @param[inout]  var   Pointer to a counter variable.
+ *
+ * @return The value of *val* before the increment.
+ */
+static inline int atomic_inc(atomic_int_t *var)
+{
+    int old;
+
+    do {
+        old = var->value;
+    } while (!atomic_cas(var, old, old + 1));
+
+    return old;
+}
+
+/**
+ * @brief Decrement a counter variable by one atomically and return the old value.
+ *
+ * @param[inout]  var   Pointer to a counter variable.
+ *
+ * @return The value of *val* before the decrement.
+ */
+static inline int atomic_dec(atomic_int_t *var)
+{
+    int old;
+
+    do {
+        old = var->value;
+    } while (!atomic_cas(var, old, old - 1));
+
+    return old;
+}
+
+/**
+ * @brief Set an atomic variable to 1.
+ *
+ * @param[inout]  var   Pointer to an atomic variable to update
+ *
+ * @return 1 if the old value was 0 and the variable was successfully updated
+ * @return 0 if the variable was already set
+ */
+static inline int atomic_set_to_one(atomic_int_t *var)
+{
+    do {
+        if (var->value != 0) {
+            return 0;
+        }
+    } while (!atomic_cas(var, 0, 1));
+
+    return 1;
+}
+
+/**
+ * @brief Set an atomic variable to 0.
+ *
+ * @param[inout]  var   Pointer to an atomic variable to update
+ *
+ * @return 1 if the old value was not 0 and the variable was successfully updated
+ * @return 0 if the variable was already cleared
+ */
+static inline int atomic_set_to_zero(atomic_int_t *var)
+{
+    int old;
+
+    do {
+        old = var->value;
+
+        if (old == 0) {
+            return 0;
+        }
+    } while (!atomic_cas(var, old, 0));
+
+    return 1;
+}
+
+/**
+ * @brief Get the value of an atomic int
+ *
+ * @param[in]  var   Atomic variable
+ *
+ * @return the value of the atomic integer
+ *
+ * @note This can be used for non-thread-safe assignment of the atomic integer
+ */
+#define ATOMIC_VALUE(var) ((var).value)
+
 #ifdef __cplusplus
 }
 #endif
 
-#endif /* _ATOMIC_H */
+#endif /* ATOMIC_H_ */
 /** @} */

cpu/atmega_common/atomic_arch.c

@@ -1,33 +0,0 @@
-/*
- * Copyright (C) 2014 Freie Universität Berlin, Hinnerk van Bruinehsen
- *
- * This file is subject to the terms and conditions of the GNU Lesser
- * General Public License v2.1. See the file LICENSE in the top level
- * directory for more details.
- */
-
-/**
- * @ingroup     cpu_atmega_common
- * @{
- *
- * @file        atomic_arch.c
- * @brief       Implementation of the kernels atomic interface
- *
- * @author      Stefan Pfeiffer <stefan.pfeiffer@fu-berlin.de>
- * @author      Hauke Petersen <hauke.petersen@fu-berlin.de>
- * @author      Hinnerk van Bruinehsen <h.v.bruinehsen@fu-berlin.de>
- *
- * @}
- */
-
-#include "arch/atomic_arch.h"
-#include "irq.h"
-
-unsigned int atomic_arch_set_return(unsigned int *to_set, unsigned int value)
-{
-    disableIRQ();
-    unsigned int old = *to_set;
-    *to_set = value;
-    enableIRQ();
-    return old;
-}

cpu/cortex-m0_common/atomic_arch.c

@@ -1,33 +0,0 @@
-/*
- * Copyright (C) 2014 Freie Universität Berlin
- *
- * This file is subject to the terms and conditions of the GNU Lesser General
- * Public License v2.1. See the file LICENSE in the top level directory for more
- * details.
- */
-
-/**
- * @ingroup     cpu_cortexm0_common
- * @{
- *
- * @file
- * @brief       Implementation of the kernels atomic interface
- *
- * @author      Stefan Pfeiffer <stefan.pfeiffer@fu-berlin.de>
- * @author      Hauke Petersen <hauke.petersen@fu-berlin.de>
- *
- * @}
- */
-
-#include "arch/atomic_arch.h"
-#include "irq.h"
-
-
-unsigned int atomic_arch_set_return(unsigned int *to_set, unsigned int value)
-{
-    disableIRQ();
-    unsigned int old = *to_set;
-    *to_set = value;
-    enableIRQ();
-    return old;
-}

cpu/cortex-m3_common/include/cpu.h

@@ -20,11 +20,17 @@
  *
  * @author      Stefan Pfeiffer <stefan.pfeiffer@fu-berlin.de>
  * @author      Hauke Petersen <hauke.petersen@fu-berlin.de>
+ * @author      Joakim Gebart <joakim.gebart@eistec.se>
  */
 
 #ifndef __CORTEXM_COMMON_H
 #define __CORTEXM_COMMON_H
 
+/**
+ * @brief Cortex-M3 has architecture specific atomic operations in atomic_arch.c.
+ */
+#define ARCH_HAS_ATOMIC_INT 1
+
 #include "cpu-conf.h"
 
 /**

cpu/cortex-m4_common/include/cpu.h

@@ -20,11 +20,17 @@
  *
  * @author      Stefan Pfeiffer <stefan.pfeiffer@fu-berlin.de>
  * @author      Hauke Petersen <hauke.petersen@fu-berlin.de>
+ * @author      Joakim Gebart <joakim.gebart@eistec.se>
  */
 
 #ifndef __CORTEXM_COMMON_H
 #define __CORTEXM_COMMON_H
 
+/**
+ * @brief Cortex-M4 has architecture specific atomic operations in atomic_arch.c.
+ */
+#define ARCH_HAS_ATOMIC_INT 1
+
 #include "cpu-conf.h"
 
 /**

cpu/msp430-common/atomic.c

@@ -1,32 +0,0 @@
-/*
- * Copyright (C) 2014 Freie Universität Berlin
- *
- * This file is subject to the terms and conditions of the GNU Lesser
- * General Public License v2.1. See the file LICENSE in the top level
- * directory for more details.
- */
-
-/**
- * @ingroup     cpu
- * @{
- *
- * @file        atomic.c
- * @brief       atomic set and return function
- *
- * @author      Kaspar Schleiser <kaspar@schleiser.de>
- * @author      Oliver Hahm <oliver.hahm@inria.fr>
- *
- * @}
- */
-
-#include "atomic.h"
-#include "cpu.h"
-
-unsigned int atomic_set_return(unsigned int *val, unsigned int set)
-{
-    dINT();
-    unsigned int old_val = *val;
-    *val = set;
-    eINT();
-    return old_val;
-}

cpu/x86/include/cpu.h

@@ -43,6 +43,11 @@
 extern "C" {
 #endif
 
+/**
+ * @brief x86 has architecture specific atomic operations in x86_atomic.c.
+ */
+#define ARCH_HAS_ATOMIC_INT 1
+
 static inline void __attribute__((always_inline)) dINT(void)
 {
     asm volatile ("cli");