posix: key: abstract pthread_key_t as uint32_t

Consistent with the change of `pthread_t`, `pthread_mutex_t`,
and `pthread_cond_t` to `uint32_t`, we can now also abstract
`pthread_key_t` as `uint32_t` and separate the implementation
detail, hidden from POSIX API consumers.

This change introduces `CONFIG_MAX_PTHREAD_KEY_COUNT`.

Signed-off-by: Chris Friedt <cfriedt@meta.com>

include/zephyr/posix/pthread_key.h

@@ -18,30 +18,7 @@ extern "C" {
 typedef uint32_t pthread_once_t;
 
 /* pthread_key */
-typedef void *pthread_key_t;
-
-typedef struct pthread_key_obj {
-	/* List of pthread_key_data objects that contain thread
-	 * specific data for the key
-	 */
-	sys_slist_t key_data_l;
-
-	/* Optional destructor that is passed to pthread_key_create() */
-	void (*destructor)(void *);
-} pthread_key_obj;
-
-typedef struct pthread_thread_data {
-	sys_snode_t node;
-
-	/* Key and thread specific data passed to pthread_setspecific() */
-	pthread_key_obj *key;
-	void *spec_data;
-} pthread_thread_data;
-
-typedef struct pthread_key_data {
-	sys_snode_t node;
-	pthread_thread_data thread_data;
-} pthread_key_data;
+typedef uint32_t pthread_key_t;
 
 #ifdef __cplusplus
 }

lib/posix/Kconfig

@@ -49,6 +49,13 @@ config MAX_PTHREAD_COND_COUNT
 	help
 	  Maximum number of simultaneously active condition variables in a POSIX application.
 
+config MAX_PTHREAD_KEY_COUNT
+	int "Maximum simultaneously active keys in a POSIX application"
+	default 5
+	range 0 255
+	help
+	  Maximum number of simultaneously active keys in a POSIX application.
+
 config SEM_VALUE_MAX
 	int "Maximum semaphore limit"
 	default 32767

lib/posix/posix_internal.h

@@ -55,6 +55,29 @@ struct posix_thread {
 	pthread_cond_t state_cond;
 };
 
+typedef struct pthread_key_obj {
+	/* List of pthread_key_data objects that contain thread
+	 * specific data for the key
+	 */
+	sys_slist_t key_data_l;
+
+	/* Optional destructor that is passed to pthread_key_create() */
+	void (*destructor)(void *value);
+} pthread_key_obj;
+
+typedef struct pthread_thread_data {
+	sys_snode_t node;
+
+	/* Key and thread specific data passed to pthread_setspecific() */
+	pthread_key_obj *key;
+	void *spec_data;
+} pthread_thread_data;
+
+typedef struct pthread_key_data {
+	sys_snode_t node;
+	pthread_thread_data thread_data;
+} pthread_key_data;
+
 static inline bool is_pthread_obj_initialized(uint32_t obj)
 {
 	return (obj & PTHREAD_OBJ_MASK_INIT) != 0;
@@ -84,4 +107,10 @@ struct posix_cond *to_posix_cond(pthread_cond_t *cvar);
 /* get a previously initialized posix_cond */
 struct posix_cond *get_posix_cond(pthread_cond_t cond);
 
+/* get and possibly initialize a posix_key */
+pthread_key_obj *to_posix_key(pthread_key_t *keyp);
+
+/* get a previously initialized posix_key */
+pthread_key_obj *get_posix_key(pthread_key_t key);
+
 #endif

lib/posix/pthread_key.c

@@ -6,11 +6,84 @@
 #include <zephyr/kernel.h>
 #include <zephyr/posix/pthread.h>
 #include <zephyr/posix/pthread_key.h>
+#include <zephyr/sys/bitarray.h>
 
 #include "posix_internal.h"
 
 static struct k_spinlock pthread_key_lock;
 
+/* This is non-standard (i.e. an implementation detail) */
+#define PTHREAD_KEY_INITIALIZER (-1)
+
+/*
+ * We reserve the MSB to mark a pthread_key_t as initialized (from the
+ * perspective of the application). With a linear space, this means that
+ * the theoretical pthread_key_t range is [0,2147483647].
+ */
+BUILD_ASSERT(CONFIG_MAX_PTHREAD_KEY_COUNT < PTHREAD_OBJ_MASK_INIT,
+	     "CONFIG_MAX_PTHREAD_KEY_COUNT is too high");
+
+static pthread_key_obj posix_key_pool[CONFIG_MAX_PTHREAD_KEY_COUNT];
+SYS_BITARRAY_DEFINE_STATIC(posix_key_bitarray, CONFIG_MAX_PTHREAD_KEY_COUNT);
+
+static inline size_t posix_key_to_offset(pthread_key_obj *k)
+{
+	return k - posix_key_pool;
+}
+
+static inline size_t to_posix_key_idx(pthread_key_t key)
+{
+	return mark_pthread_obj_uninitialized(key);
+}
+
+pthread_key_obj *get_posix_key(pthread_key_t key)
+{
+	int actually_initialized;
+	size_t bit = to_posix_key_idx(key);
+
+	/* if the provided cond does not claim to be initialized, its invalid */
+	if (!is_pthread_obj_initialized(key)) {
+		return NULL;
+	}
+
+	/* Mask off the MSB to get the actual bit index */
+	if (sys_bitarray_test_bit(&posix_key_bitarray, bit, &actually_initialized) < 0) {
+		return NULL;
+	}
+
+	if (actually_initialized == 0) {
+		/* The cond claims to be initialized but is actually not */
+		return NULL;
+	}
+
+	return &posix_key_pool[bit];
+}
+
+pthread_key_obj *to_posix_key(pthread_key_t *key)
+{
+	size_t bit;
+	pthread_key_obj *k;
+
+	if (*key != PTHREAD_KEY_INITIALIZER) {
+		return get_posix_key(*key);
+	}
+
+	/* Try and automatically associate a pthread_key_obj */
+	if (sys_bitarray_alloc(&posix_key_bitarray, 1, &bit) < 0) {
+		/* No keys left to allocate */
+		return NULL;
+	}
+
+	/* Record the associated posix_cond in mu and mark as initialized */
+	*key = mark_pthread_obj_initialized(bit);
+	k = &posix_key_pool[bit];
+
+	/* Initialize the condition variable here */
+	memset(k, 0, sizeof(*k));
+
+	return k;
+}
+
 /**
  * @brief Create a key for thread-specific data
  *
@@ -21,10 +94,8 @@ int pthread_key_create(pthread_key_t *key,
 {
 	pthread_key_obj *new_key;
 
-	*key = NULL;
-
-	new_key = k_malloc(sizeof(pthread_key_obj));
-
+	*key = PTHREAD_KEY_INITIALIZER;
+	new_key = to_posix_key(key);
 	if (new_key == NULL) {
 		return ENOMEM;
 	}
@@ -32,7 +103,6 @@ int pthread_key_create(pthread_key_t *key,
 	sys_slist_init(&(new_key->key_data_l));
 
 	new_key->destructor = destructor;
-	*key = (void *)new_key;
 
 	return 0;
 }
@@ -44,13 +114,19 @@ int pthread_key_create(pthread_key_t *key,
  */
 int pthread_key_delete(pthread_key_t key)
 {
-	pthread_key_obj *key_obj = (pthread_key_obj *)key;
+	pthread_key_obj *key_obj;
 	pthread_key_data *key_data;
 	sys_snode_t *node_l, *next_node_l;
 	k_spinlock_key_t key_key;
 
 	key_key = k_spin_lock(&pthread_key_lock);
 
+	key_obj = get_posix_key(key);
+	if (key_obj == NULL) {
+		k_spin_unlock(&pthread_key_lock, key_key);
+		return EINVAL;
+	}
+
 	/* Delete thread-specific elements associated with the key */
 	SYS_SLIST_FOR_EACH_NODE_SAFE(&(key_obj->key_data_l),
 			node_l, next_node_l) {
@@ -63,7 +139,7 @@ int pthread_key_delete(pthread_key_t key)
 		k_free((void *)key_data);
 	}
 
-	k_free((void *)key_obj);
+	(void)sys_bitarray_free(&posix_key_bitarray, 1, 0);
 
 	k_spin_unlock(&pthread_key_lock, key_key);
 
@@ -77,7 +153,7 @@ int pthread_key_delete(pthread_key_t key)
  */
 int pthread_setspecific(pthread_key_t key, const void *value)
 {
-	pthread_key_obj *key_obj = (pthread_key_obj *)key;
+	pthread_key_obj *key_obj;
 	struct posix_thread *thread = to_posix_thread(pthread_self());
 	pthread_key_data *key_data;
 	pthread_thread_data *thread_spec_data;
@@ -91,6 +167,12 @@ int pthread_setspecific(pthread_key_t key, const void *value)
 	 */
 	key_key = k_spin_lock(&pthread_key_lock);
 
+	key_obj = get_posix_key(key);
+	if (key_obj == NULL) {
+		k_spin_unlock(&pthread_key_lock, key_key);
+		return EINVAL;
+	}
+
 	SYS_SLIST_FOR_EACH_NODE(&(thread->key_list), node_l) {
 
 			thread_spec_data = (pthread_thread_data *)node_l;
@@ -114,7 +196,7 @@ int pthread_setspecific(pthread_key_t key, const void *value)
 
 		} else {
 			/* Associate thread specific data, initialize new key */
-			key_data->thread_data.key = key;
+			key_data->thread_data.key = key_obj;
 			key_data->thread_data.spec_data = (void *)value;
 
 			/* Append new thread key data to thread's key list */
@@ -140,7 +222,7 @@ out:
  */
 void *pthread_getspecific(pthread_key_t key)
 {
-	pthread_key_obj *key_obj = (pthread_key_obj *)key;
+	pthread_key_obj *key_obj;
 	struct posix_thread *thread = to_posix_thread(pthread_self());
 	pthread_thread_data *thread_spec_data;
 	void *value = NULL;
@@ -149,6 +231,12 @@ void *pthread_getspecific(pthread_key_t key)
 
 	key_key = k_spin_lock(&pthread_key_lock);
 
+	key_obj = get_posix_key(key);
+	if (key_obj == NULL) {
+		k_spin_unlock(&pthread_key_lock, key_key);
+		return NULL;
+	}
+
 	node_l = sys_slist_peek_head(&(thread->key_list));
 
 	/* Traverse the list of keys set by the thread, looking for key */