diff options
Diffstat (limited to 'Python/thread.c')
| -rw-r--r-- | Python/thread.c | 90 |
1 files changed, 84 insertions, 6 deletions
diff --git a/Python/thread.c b/Python/thread.c index 3985779..b1ddf53 100644 --- a/Python/thread.c +++ b/Python/thread.c @@ -142,26 +142,80 @@ void PyThread_init_thread(void) This code stolen from "thread_sgi.h", where it was the only implementation of an existing Python TLS API. */ -/* - * Per-thread data ("key") support. - */ +/* ------------------------------------------------------------------------ +Per-thread data ("key") support. + +Use PyThread_create_key() to create a new key. This is typically shared +across threads. + +Use PyThread_set_key_value(thekey, value) to associate void* value with +thekey in the current thread. Each thread has a distinct mapping of thekey +to a void* value. Caution: if the current thread already has a mapping +for thekey, value is ignored. + +Use PyThread_get_key_value(thekey) to retrieve the void* value associated +with thekey in the current thread. This returns NULL if no value is +associated with thekey in the current thread. + +Use PyThread_delete_key_value(thekey) to forget the current thread's associated +value for thekey. PyThread_delete_key(thekey) forgets the values associated +with thekey across *all* threads. +While some of these functions have error-return values, none set any +Python exception. + +None of the functions does memory management on behalf of the void* values. +You need to allocate and deallocate them yourself. If the void* values +happen to be PyObject*, these functions don't do refcount operations on +them either. + +The GIL does not need to be held when calling these functions; they supply +their own locking. This isn't true of PyThread_create_key(), though (see +next paragraph). + +There's a hidden assumption that PyThread_create_key() will be called before +any of the other functions are called. There's also a hidden assumption +that calls to PyThread_create_key() are serialized externally. +------------------------------------------------------------------------ */ + +/* A singly-linked list of struct key objects remembers all the key->value + * associations. File static keyhead heads the list. keymutex is used + * to enforce exclusion internally. + */ struct key { + /* Next record in the list, or NULL if this is the last record. */ struct key *next; + + /* The thread id, according to PyThread_get_thread_ident(). */ long id; + + /* The key and its associated value. */ int key; void *value; }; static struct key *keyhead = NULL; -static int nkeys = 0; static PyThread_type_lock keymutex = NULL; - +static int nkeys = 0; /* PyThread_create_key() hands out nkeys+1 next */ + +/* Internal helper. + * If the current thread has a mapping for key, the appropriate struct key* + * is returned. NB: value is ignored in this case! + * If there is no mapping for key in the current thread, then: + * If value is NULL, NULL is returned. + * Else a mapping of key to value is created for the current thread, + * and a pointer to a new struct key* is returned; except that if + * malloc() can't find room for a new struct key*, NULL is returned. + * So when value==NULL, this acts like a pure lookup routine, and when + * value!=NULL, this acts like dict.setdefault(), returning an existing + * mapping if one exists, else creating a new mapping. + */ static struct key * find_key(int key, void *value) { struct key *p; long id = PyThread_get_thread_ident(); + for (p = keyhead; p != NULL; p = p->next) { if (p->id == id && p->key == key) return p; @@ -181,18 +235,27 @@ find_key(int key, void *value) return p; } +/* Return a new key. This must be called before any other functions in + * this family, and callers must arrange to serialize calls to this + * function. No violations are detected. + */ int PyThread_create_key(void) { + /* All parts of this function are wrong if it's called by multiple + * threads simultaneously. + */ if (keymutex == NULL) keymutex = PyThread_allocate_lock(); return ++nkeys; } +/* Forget the associations for key across *all* threads. */ void PyThread_delete_key(int key) { struct key *p, **q; + PyThread_acquire_lock(keymutex, 1); q = &keyhead; while ((p = *q) != NULL) { @@ -207,31 +270,46 @@ PyThread_delete_key(int key) PyThread_release_lock(keymutex); } +/* Confusing: If the current thread has an association for key, + * value is ignored, and 0 is returned. Else an attempt is made to create + * an association of key to value for the current thread. 0 is returned + * if that succeeds, but -1 is returned if there's not enough memory + * to create the association. value must not be NULL. + */ int PyThread_set_key_value(int key, void *value) { - struct key *p = find_key(key, value); + struct key *p; + + assert(value != NULL); + p = find_key(key, value); if (p == NULL) return -1; else return 0; } +/* Retrieve the value associated with key in the current thread, or NULL + * if the current thread doesn't have an association for key. + */ void * PyThread_get_key_value(int key) { struct key *p = find_key(key, NULL); + if (p == NULL) return NULL; else return p->value; } +/* Forget the current thread's association for key, if any. */ void PyThread_delete_key_value(int key) { long id = PyThread_get_thread_ident(); struct key *p, **q; + PyThread_acquire_lock(keymutex, 1); q = &keyhead; while ((p = *q) != NULL) { |