Add some thread coordination primitives.

Due to the nature of event loops, it is a bit difficult to integrate
lock and other primitives such that they don't block fibers on the same
thread.

src/core/abstract.c

@@ -106,6 +106,7 @@ void janet_os_mutex_lock(JanetOSMutex *mutex) {
 }
 
 void janet_os_mutex_unlock(JanetOSMutex *mutex) {
+    /* error handling? May want to keep counter */
     LeaveCriticalSection((CRITICAL_SECTION *) mutex);
 }
 
@@ -120,7 +121,10 @@ static int32_t janet_decref(JanetAbstractHead *ab) {
 }
 
 void janet_os_mutex_init(JanetOSMutex *mutex) {
-    pthread_mutex_init(mutex, NULL);
+    pthread_mutexattr_t attr;
+    pthread_mutexattr_init(&attr);
+    pthread_mutexattr_settype(&attr, PTHREAD_MUTEX_RECURSIVE);
+    pthread_mutex_init(mutex, &attr);
 }
 
 void janet_os_mutex_deinit(JanetOSMutex *mutex) {
@@ -132,7 +136,8 @@ void janet_os_mutex_lock(JanetOSMutex *mutex) {
 }
 
 void janet_os_mutex_unlock(JanetOSMutex *mutex) {
-    pthread_mutex_unlock(mutex);
+    int ret = pthread_mutex_unlock(mutex);
+    if (ret) janet_panic("cannot release lock");
 }
 
 #endif

src/core/ev.c

@@ -3013,6 +3013,54 @@ JANET_CORE_FN(janet_cfun_stream_write,
     janet_await();
 }
 
+typedef struct {
+    JanetOSMutex mutex;
+    int destroyed;
+} JanetAbstractMutex;
+
+static int mutexgc(void *p, size_t size) {
+    JanetAbstractMutex *mutex = (JanetAbstractMutex *) p;
+    (void) size;
+    janet_os_mutex_deinit(&mutex->mutex);
+    return 0;
+}
+
+const JanetAbstractType janet_mutex_type = {
+    "core/lock",
+    mutexgc,
+    JANET_ATEND_GC
+};
+
+JANET_CORE_FN(janet_cfun_mutex,
+        "(ev/lock)",
+        "Create a new lock to coordinate threads.") {
+    janet_fixarity(argc, 0);
+    (void) argv;
+    JanetAbstractMutex *mutex = janet_abstract_threaded(&janet_mutex_type, sizeof(JanetAbstractMutex));
+    janet_os_mutex_init(&mutex->mutex);
+    return janet_wrap_abstract(mutex);
+}
+
+JANET_CORE_FN(janet_cfun_mutex_acquire,
+        "(ev/acquire-lock lock)",
+        "Acquire a lock such that this operating system thread is the only thread with access to this resource."
+        " This will block this entire thread until the lock becomes available, and will not yield to other fibers "
+        "on this system thread.") {
+    janet_fixarity(argc, 1);
+    JanetAbstractMutex *mutex = janet_getabstract(argv, 0, &janet_mutex_type);
+    janet_os_mutex_lock(&mutex->mutex);
+    return argv[0];
+}
+
+JANET_CORE_FN(janet_cfun_mutex_release,
+        "(ev/release-lock lock)",
+        "Release a lock such that other threads may acquire it.") {
+    janet_fixarity(argc, 1);
+    JanetAbstractMutex *mutex = janet_getabstract(argv, 0, &janet_mutex_type);
+    janet_os_mutex_unlock(&mutex->mutex);
+    return argv[0];
+}
+
 void janet_lib_ev(JanetTable *env) {
     JanetRegExt ev_cfuns_ext[] = {
         JANET_CORE_REG("ev/give", cfun_channel_push),
@@ -3035,12 +3083,16 @@ void janet_lib_ev(JanetTable *env) {
         JANET_CORE_REG("ev/read", janet_cfun_stream_read),
         JANET_CORE_REG("ev/chunk", janet_cfun_stream_chunk),
         JANET_CORE_REG("ev/write", janet_cfun_stream_write),
+        JANET_CORE_REG("ev/lock", janet_cfun_mutex),
+        JANET_CORE_REG("ev/acquire-lock", janet_cfun_mutex_acquire),
+        JANET_CORE_REG("ev/release-lock", janet_cfun_mutex_release),
         JANET_REG_END
     };
 
     janet_core_cfuns_ext(env, NULL, ev_cfuns_ext);
     janet_register_abstract_type(&janet_stream_type);
     janet_register_abstract_type(&janet_channel_type);
+    janet_register_abstract_type(&janet_mutex_type);
 }
 
 #endif

src/include/janet.h

@@ -1180,17 +1180,6 @@ typedef struct {
     Janet payload;
 } JanetTryState;
 
-/* Thread types */
-#ifdef JANET_THREADS
-typedef struct JanetThread JanetThread;
-typedef struct JanetMailbox JanetMailbox;
-struct JanetThread {
-    JanetMailbox *mailbox;
-    JanetTable *encode;
-};
-#endif
-
-
 /***** END SECTION TYPES *****/
 
 /***** START SECTION OPCODES *****/
@@ -2078,16 +2067,6 @@ JANET_API int janet_scan_uint64(const uint8_t *str, int32_t len, uint64_t *out);
 
 #endif
 
-#ifdef JANET_THREADS
-
-extern JANET_API const JanetAbstractType janet_thread_type;
-
-JANET_API int janet_thread_receive(Janet *msg_out, double timeout);
-JANET_API int janet_thread_send(JanetThread *thread, Janet msg, double timeout);
-JANET_API JanetThread *janet_thread_current(void);
-
-#endif
-
 /* Custom allocator support */
 JANET_API void *(janet_malloc)(size_t);
 JANET_API void *(janet_realloc)(void *, size_t);