Merge pull request #3856 from BsAtHome/fix_rtapi-atomics

Fix rtapi atomics

Author: andypugh

src/hal/hal.h

@@ -339,13 +339,6 @@ typedef union {
     hal_u64_t lu;
 } hal_data_u;
 
-typedef struct {
-    volatile unsigned int read;  //offset into buff that outgoing data gets read from
-    volatile unsigned int write; //offset into buff that incoming data gets written to
-    unsigned int size;           //size of allocated buffer
-    char buff[];
-} hal_port_shm_t;
-
 /***********************************************************************
 *                      "LOCKING" FUNCTIONS                             *
 ************************************************************************/
@@ -945,6 +938,7 @@ union hal_stream_data {
     uint32_t u;
 };
 
+struct hal_stream_shm; // Forward declaration. Only relevant in hal_lib.c.
 typedef struct {
     int comp_id, shmem_id;
     struct hal_stream_shm *fifo;

src/hal/hal_lib.c

@@ -3762,6 +3762,15 @@ static char *halpr_type_string(int type, char *buf, size_t nbuf) {
 HAL PORT functions
 ******************************************************************************/
 
+// This struct is purely local to this file to keep track of the
+// port data in shmem.
+typedef struct __hal_port_shm_t {
+    atomic_uint read;  // offset into buff that outgoing data gets read from
+    atomic_uint write; // offset into buff that incoming data gets written to
+    unsigned int size; // size of allocated buffer
+    char buff[];
+} hal_port_shm_t;
+
 static void hal_port_atomic_load(hal_port_shm_t* port_shm, unsigned* read, unsigned* write)
 {
     *read = atomic_load_explicit(&port_shm->read, memory_order_acquire);
@@ -4067,6 +4076,22 @@ void hal_port_wait_writable(hal_port_t** port, unsigned count, sig_atomic_t* sto
 /*
 hal stream implementation
 */
+
+// This struct is purely local to this file to keep track of the stream
+// data in shmem.
+struct hal_stream_shm {
+    unsigned magic;
+    atomic_uint in;
+    atomic_uint out;
+    unsigned this_sample;
+    unsigned depth;
+    int num_pins;
+    atomic_uint num_overruns;
+    atomic_uint num_underruns;
+    hal_type_t type[HAL_STREAM_MAX_PINS];
+    union hal_stream_data data[];
+};
+
 int halpr_parse_types(hal_type_t type[HAL_STREAM_MAX_PINS], const char *cfg)
 {
     const char *c;

src/hal/hal_priv.h

@@ -494,17 +494,6 @@ extern int hal_port_alloc(unsigned size, hal_port_t *port);
 
 
 #define HAL_STREAM_MAGIC_NUM		0x4649464F
-struct hal_stream_shm {
-    unsigned magic;
-    volatile unsigned in;
-    volatile unsigned out;
-    unsigned this_sample;
-    unsigned depth;
-    int num_pins;
-    unsigned long num_overruns, num_underruns;
-    hal_type_t type[HAL_STREAM_MAX_PINS];
-    union hal_stream_data data[];
-};
 
 extern int halpr_parse_types(hal_type_t type[HAL_STREAM_MAX_PINS], const char *fcg);
 RTAPI_END_DECLS

src/rtapi/rtapi_atomic.h

@@ -1,4 +1,5 @@
 //    Copyright 2015 Jeff Epler
+//    Copyright 2026 B.Stultiens
 //
 //    This program is free software; you can redistribute it and/or modify
 //    it under the terms of the GNU General Public License as published by
@@ -16,35 +17,33 @@
 #ifndef __LINUXCNC_RTAPI_ATOMIC_H
 #define __LINUXCNC_RTAPI_ATOMIC_H
 
-#if defined(__GNUC__) && ((__GNUC__ << 8) | __GNUC_MINOR__) >= 0x409
+#if defined(__cplusplus)
+
+// We use C++20 and that has all the atomics we need
+#include <atomic>
+
+#else // defined(__cplusplus)
+
+// Standard C, we require C11 or better
+#if defined(__STDC_VERSION__) && __STDC_VERSION__ >= 201112L
 #define RTAPI_USE_STDATOMIC
-#elif defined(__STDC_VERSION__) && __STDC_VERSION > 201112L
+#elif defined(__GNUC__) && ((__GNUC__ << 8) | __GNUC_MINOR__) >= 0x409
 #define RTAPI_USE_STDATOMIC
 #endif
 
-#ifdef RTAPI_USE_STDATOMIC
+#if defined(RTAPI_USE_STDATOMIC)
 #include <stdatomic.h>
-#else
 
-enum memory_order {
-    memory_order_relaxed,
-    memory_order_consume,
-    memory_order_acquire,
-    memory_order_release,
-    memory_order_acq_rel,
-    memory_order_seq_cst
-};
+#if defined(__STDC_NO_ATOMICS__)
+#error "Your compiler/libc has set __STDC_NO_ATOMICS__ and atomics are required."
+#endif
 
-#define atomic_store(obj, desired) atomic_store_explicit((obj), (desired), memory_order_seq_cst)
-#define atomic_load(obj) atomic_load_explicit((obj), memory_order_seq_cst)
+#else // defined(RTAPI_USE_STDATOMIC)
 
-// note that in this implementation, only one level of synchronization is supported, equivalent to memory_order_seq_cst
-#define atomic_store_explicit(obj, desired, order) \
-    ({ (void)order; __sync_synchronize(); *(obj) = (desired); (void)0; })
+#error "Old compiler has no C11 atomics. Please upgrade your compiler to support C11 or better."
 
-#define atomic_load_explicit(obj, order) \
-    ({ (void)order; __typeof__(*(obj)) v = *(obj); __sync_synchronize(); v; })
+#endif // defined(RTAPI_USE_STDATOMIC)
 
-#endif
+#endif // defined(__cplusplus)
 
 #endif

src/rtapi/rtapi_uspace.hh

@@ -22,7 +22,7 @@
 #endif
 #include <unistd.h>
 #include <pthread.h>
-#include <atomic>
+#include "rtapi_atomic.h"
 
 static inline void rtapi_timespec_add(timespec &result, const timespec &ta, const timespec &tb) {
     result.tv_sec = ta.tv_sec + tb.tv_sec;
@@ -45,7 +45,7 @@ struct WithRoot
 {
     WithRoot();
     ~WithRoot();
-    static std::atomic<int> level;
+    static std::atomic_int level;
 };
 
 struct rtapi_task {

src/rtapi/uspace_rtai.cc

@@ -5,7 +5,6 @@
 #pragma GCC diagnostic ignored "-Wnarrowing"
 #include <rtai_lxrt.h>
 #pragma GCC diagnostic pop
-#include <atomic>
 #ifdef HAVE_SYS_IO_H
 #include <sys/io.h>
 #endif
@@ -16,7 +15,7 @@ RtapiApp *app;
 
 struct RtaiTask : rtapi_task {
     RtaiTask() : rtapi_task{}, cancel{}, rt_task{}, thr{} {}
-    std::atomic<int> cancel;
+    std::atomic_int cancel;
     RT_TASK *rt_task;
     pthread_t thr;
 };

src/rtapi/uspace_rtapi_app.cc

@@ -51,14 +51,14 @@
 #include <pthread_np.h>
 #endif
 
+#include <boost/lockfree/queue.hpp>
+
 #include "rtapi.h"
 #include <hal.h>
 #include "hal/hal_priv.h"
 #include "rtapi_uspace.hh"
 
-#include <boost/lockfree/queue.hpp>
-
-std::atomic<int> WithRoot::level;
+std::atomic_int WithRoot::level;
 static uid_t euid, ruid;
 
 #include "rtapi/uspace_common.h"

src/rtapi/uspace_xenomai.cc

@@ -5,7 +5,6 @@
 #include  <errno.h>
 #include <stdio.h>
 #include <cstring>
-#include <atomic>
 #ifdef HAVE_SYS_IO_H
 #include <sys/io.h>
 #endif
@@ -14,7 +13,7 @@ namespace
 {
 struct RtaiTask : rtapi_task {
     RtaiTask() : rtapi_task{}, cancel{}, thr{} {}
-    std::atomic<int> cancel;
+    std::atomic_int cancel;
     pthread_t thr;
 };