unix: Implement MICROPY_BEGIN/END_ATOMIC_SECTION protection macros.

This macro is used to implement global serialisation, typically by
disabling IRQs.  On the unix port, if threading is enabled, use the
existing thread mutex (that protects the thread list structure) for this
purpose.  Other places in the code (eg the scheduler) assume this macro
will provide serialisation.

ports/unix/mpconfigport.h

@@ -342,4 +342,9 @@ void mp_unix_mark_exec(void);
 #include <stdio.h>
 #endif
 
+#if MICROPY_PY_THREAD
+#define MICROPY_BEGIN_ATOMIC_SECTION() (mp_thread_unix_begin_atomic_section(), 0)
+#define MICROPY_END_ATOMIC_SECTION(x) (void)x; mp_thread_unix_end_atomic_section()
+#endif
+
 #endif // MICROPY_UNIX_MINIMAL

ports/unix/mpthreadport.c

@@ -60,7 +60,9 @@ typedef struct _thread_t {
 
 STATIC pthread_key_t tls_key;
 
-// the mutex controls access to the linked list
+// The mutex is used for any code in this port that needs to be thread safe.
+// Specifically for thread management, access to the linked list is one example.
+// But also, e.g. scheduler state.
 STATIC pthread_mutex_t thread_mutex = PTHREAD_MUTEX_INITIALIZER;
 STATIC thread_t *thread;
 
@@ -73,6 +75,14 @@ STATIC sem_t *thread_signal_done_p;
 STATIC sem_t thread_signal_done;
 #endif
 
+void mp_thread_unix_begin_atomic_section(void) {
+    pthread_mutex_lock(&thread_mutex);
+}
+
+void mp_thread_unix_end_atomic_section(void) {
+    pthread_mutex_unlock(&thread_mutex);
+}
+
 // this signal handler is used to scan the regs and stack of a thread
 STATIC void mp_thread_gc(int signo, siginfo_t *info, void *context) {
     (void)info; // unused
@@ -123,14 +133,14 @@ void mp_thread_init(void) {
 }
 
 void mp_thread_deinit(void) {
-    pthread_mutex_lock(&thread_mutex);
+    mp_thread_unix_begin_atomic_section();
     while (thread->next != NULL) {
         thread_t *th = thread;
         thread = thread->next;
         pthread_cancel(th->id);
         free(th);
     }
-    pthread_mutex_unlock(&thread_mutex);
+    mp_thread_unix_end_atomic_section();
     #if defined(__APPLE__)
     sem_close(thread_signal_done_p);
     sem_unlink(thread_signal_done_name);
@@ -146,7 +156,7 @@ void mp_thread_deinit(void) {
 // the global root pointers (in mp_state_ctx) while another thread is doing a
 // garbage collection and tracing these pointers.
 void mp_thread_gc_others(void) {
-    pthread_mutex_lock(&thread_mutex);
+    mp_thread_unix_begin_atomic_section();
     for (thread_t *th = thread; th != NULL; th = th->next) {
         gc_collect_root(&th->arg, 1);
         if (th->id == pthread_self()) {
@@ -162,7 +172,7 @@ void mp_thread_gc_others(void) {
         sem_wait(&thread_signal_done);
         #endif
     }
-    pthread_mutex_unlock(&thread_mutex);
+    mp_thread_unix_end_atomic_section();
 }
 
 mp_state_thread_t *mp_thread_get_state(void) {
@@ -175,14 +185,14 @@ void mp_thread_set_state(mp_state_thread_t *state) {
 
 void mp_thread_start(void) {
     pthread_setcanceltype(PTHREAD_CANCEL_ASYNCHRONOUS, NULL);
-    pthread_mutex_lock(&thread_mutex);
+    mp_thread_unix_begin_atomic_section();
     for (thread_t *th = thread; th != NULL; th = th->next) {
         if (th->id == pthread_self()) {
             th->ready = 1;
             break;
         }
     }
-    pthread_mutex_unlock(&thread_mutex);
+    mp_thread_unix_end_atomic_section();
 }
 
 void mp_thread_create(void *(*entry)(void *), void *arg, size_t *stack_size) {
@@ -217,13 +227,13 @@ void mp_thread_create(void *(*entry)(void *), void *arg, size_t *stack_size) {
         goto er;
     }
 
-    pthread_mutex_lock(&thread_mutex);
+    mp_thread_unix_begin_atomic_section();
 
     // create thread
     pthread_t id;
     ret = pthread_create(&id, &attr, entry, arg);
     if (ret != 0) {
-        pthread_mutex_unlock(&thread_mutex);
+        mp_thread_unix_end_atomic_section();
         goto er;
     }
 
@@ -238,7 +248,7 @@ void mp_thread_create(void *(*entry)(void *), void *arg, size_t *stack_size) {
     th->next = thread;
     thread = th;
 
-    pthread_mutex_unlock(&thread_mutex);
+    mp_thread_unix_end_atomic_section();
 
     return;
 
@@ -247,7 +257,7 @@ er:
 }
 
 void mp_thread_finish(void) {
-    pthread_mutex_lock(&thread_mutex);
+    mp_thread_unix_begin_atomic_section();
     thread_t *prev = NULL;
     for (thread_t *th = thread; th != NULL; th = th->next) {
         if (th->id == pthread_self()) {
@@ -261,7 +271,7 @@ void mp_thread_finish(void) {
         }
         prev = th;
     }
-    pthread_mutex_unlock(&thread_mutex);
+    mp_thread_unix_end_atomic_section();
 }
 
 void mp_thread_mutex_init(mp_thread_mutex_t *mutex) {

ports/unix/mpthreadport.h

@@ -31,3 +31,8 @@ typedef pthread_mutex_t mp_thread_mutex_t;
 void mp_thread_init(void);
 void mp_thread_deinit(void);
 void mp_thread_gc_others(void);
+
+// Unix version of "enable/disable IRQs".
+// Functions as a port-global lock for any code that must be serialised.
+void mp_thread_unix_begin_atomic_section(void);
+void mp_thread_unix_end_atomic_section(void);