core: Move TLS to task::local_data

1 files changed, 346 insertions, 0 deletions

diff --git a/src/libcore/task/local_data.rs b/src/libcore/task/local_data.rs
new file mode 100644
index 00000000000..4fbf0475c0a
--- /dev/null
+++ b/src/libcore/task/local_data.rs
@@ -0,0 +1,346 @@
+/*!
+
+Task local data management
+
+Allows storing boxes with arbitrary types inside, to be accessed anywhere
+within a task, keyed by a pointer to a global finaliser function. Useful
+for task-spawning metadata (tracking linked failure state), dynamic
+variables, and interfacing with foreign code with bad callback interfaces.
+
+To use, declare a monomorphic global function at the type to store, and use
+it as the 'key' when accessing. See the 'tls' tests below for examples.
+
+Casting 'Arcane Sight' reveals an overwhelming aura of Transmutation magic.
+
+*/
+
+export local_data_key;
+export local_data_pop;
+export local_data_get;
+export local_data_set;
+export local_data_modify;
+
+// XXX: These shouldn't be exported but they are used by task.rs
+export local_get;
+export local_set;
+
+/**
+ * Indexes a task-local data slot. The function's code pointer is used for
+ * comparison. Recommended use is to write an empty function for each desired
+ * task-local data slot (and use class destructors, not code inside the
+ * function, if specific teardown is needed). DO NOT use multiple
+ * instantiations of a single polymorphic function to index data of different
+ * types; arbitrary type coercion is possible this way.
+ *
+ * One other exception is that this global state can be used in a destructor
+ * context to create a circular @-box reference, which will crash during task
+ * failure (see issue #3039).
+ *
+ * These two cases aside, the interface is safe.
+ */
+type LocalDataKey<T: Owned> = &fn(+@T);
+
+trait LocalData { }
+impl<T: Owned> @T: LocalData { }
+
+impl LocalData: Eq {
+    pure fn eq(&&other: LocalData) -> bool unsafe {
+        let ptr_a: (uint, uint) = cast::reinterpret_cast(&self);
+        let ptr_b: (uint, uint) = cast::reinterpret_cast(&other);
+        return ptr_a == ptr_b;
+    }
+    pure fn ne(&&other: LocalData) -> bool { !self.eq(other) }
+}
+
+// We use dvec because it's the best data structure in core. If TLS is used
+// heavily in future, this could be made more efficient with a proper map.
+type TaskLocalElement = (*libc::c_void, *libc::c_void, LocalData);
+// Has to be a pointer at outermost layer; the foreign call returns void *.
+type TaskLocalMap = @dvec::DVec<Option<TaskLocalElement>>;
+
+extern fn cleanup_task_local_map(map_ptr: *libc::c_void) unsafe {
+    assert !map_ptr.is_null();
+    // Get and keep the single reference that was created at the beginning.
+    let _map: TaskLocalMap = cast::reinterpret_cast(&map_ptr);
+    // All local_data will be destroyed along with the map.
+}
+
+// Gets the map from the runtime. Lazily initialises if not done so already.
+unsafe fn get_task_local_map(task: *rust_task) -> TaskLocalMap {
+
+    // Relies on the runtime initialising the pointer to null.
+    // NOTE: The map's box lives in TLS invisibly referenced once. Each time
+    // we retrieve it for get/set, we make another reference, which get/set
+    // drop when they finish. No "re-storing after modifying" is needed.
+    let map_ptr = rustrt::rust_get_task_local_data(task);
+    if map_ptr.is_null() {
+        let map: TaskLocalMap = @dvec::DVec();
+        // Use reinterpret_cast -- transmute would take map away from us also.
+        rustrt::rust_set_task_local_data(
+            task, cast::reinterpret_cast(&map));
+        rustrt::rust_task_local_data_atexit(task, cleanup_task_local_map);
+        // Also need to reference it an extra time to keep it for now.
+        cast::bump_box_refcount(map);
+        map
+    } else {
+        let map = cast::transmute(move map_ptr);
+        cast::bump_box_refcount(map);
+        map
+    }
+}
+
+unsafe fn key_to_key_value<T: Owned>(
+    key: LocalDataKey<T>) -> *libc::c_void {
+
+    // Keys are closures, which are (fnptr,envptr) pairs. Use fnptr.
+    // Use reintepret_cast -- transmute would leak (forget) the closure.
+    let pair: (*libc::c_void, *libc::c_void) = cast::reinterpret_cast(&key);
+    pair.first()
+}
+
+// If returning Some(..), returns with @T with the map's reference. Careful!
+unsafe fn local_data_lookup<T: Owned>(
+    map: TaskLocalMap, key: LocalDataKey<T>)
+    -> Option<(uint, *libc::c_void)> {
+
+    let key_value = key_to_key_value(key);
+    let map_pos = (*map).position(|entry|
+        match entry {
+            Some((k,_,_)) => k == key_value,
+            None => false
+        }
+    );
+    do map_pos.map |index| {
+        // .get() is guaranteed because of "None { false }" above.
+        let (_, data_ptr, _) = (*map)[index].get();
+        (index, data_ptr)
+    }
+}
+
+unsafe fn local_get_helper<T: Owned>(
+    task: *rust_task, key: LocalDataKey<T>,
+    do_pop: bool) -> Option<@T> {
+
+    let map = get_task_local_map(task);
+    // Interpreturn our findings from the map
+    do local_data_lookup(map, key).map |result| {
+        // A reference count magically appears on 'data' out of thin air. It
+        // was referenced in the local_data box, though, not here, so before
+        // overwriting the local_data_box we need to give an extra reference.
+        // We must also give an extra reference when not removing.
+        let (index, data_ptr) = result;
+        let data: @T = cast::transmute(move data_ptr);
+        cast::bump_box_refcount(data);
+        if do_pop {
+            (*map).set_elt(index, None);
+        }
+        data
+    }
+}
+
+unsafe fn local_pop<T: Owned>(
+    task: *rust_task,
+    key: LocalDataKey<T>) -> Option<@T> {
+
+    local_get_helper(task, key, true)
+}
+
+unsafe fn local_get<T: Owned>(
+    task: *rust_task,
+    key: LocalDataKey<T>) -> Option<@T> {
+
+    local_get_helper(task, key, false)
+}
+
+unsafe fn local_set<T: Owned>(
+    task: *rust_task, key: LocalDataKey<T>, +data: @T) {
+
+    let map = get_task_local_map(task);
+    // Store key+data as *voids. Data is invisibly referenced once; key isn't.
+    let keyval = key_to_key_value(key);
+    // We keep the data in two forms: one as an unsafe pointer, so we can get
+    // it back by casting; another in an existential box, so the reference we
+    // own on it can be dropped when the box is destroyed. The unsafe pointer
+    // does not have a reference associated with it, so it may become invalid
+    // when the box is destroyed.
+    let data_ptr = cast::reinterpret_cast(&data);
+    let data_box = data as LocalData;
+    // Construct new entry to store in the map.
+    let new_entry = Some((keyval, data_ptr, data_box));
+    // Find a place to put it.
+    match local_data_lookup(map, key) {
+        Some((index, _old_data_ptr)) => {
+            // Key already had a value set, _old_data_ptr, whose reference
+            // will get dropped when the local_data box is overwritten.
+            (*map).set_elt(index, new_entry);
+        }
+        None => {
+            // Find an empty slot. If not, grow the vector.
+            match (*map).position(|x| x.is_none()) {
+                Some(empty_index) => (*map).set_elt(empty_index, new_entry),
+                None => (*map).push(new_entry)
+            }
+        }
+    }
+}
+
+unsafe fn local_modify<T: Owned>(
+    task: *rust_task, key: LocalDataKey<T>,
+    modify_fn: fn(Option<@T>) -> Option<@T>) {
+
+    // Could be more efficient by doing the lookup work, but this is easy.
+    let newdata = modify_fn(local_pop(task, key));
+    if newdata.is_some() {
+        local_set(task, key, option::unwrap(move newdata));
+    }
+}
+
+/* Exported interface for task-local data (plus local_data_key above). */
+/**
+ * Remove a task-local data value from the table, returning the
+ * reference that was originally created to insert it.
+ */
+unsafe fn local_data_pop<T: Owned>(
+    key: LocalDataKey<T>) -> Option<@T> {
+
+    local_pop(rustrt::rust_get_task(), key)
+}
+/**
+ * Retrieve a task-local data value. It will also be kept alive in the
+ * table until explicitly removed.
+ */
+unsafe fn local_data_get<T: Owned>(
+    key: LocalDataKey<T>) -> Option<@T> {
+
+    local_get(rustrt::rust_get_task(), key)
+}
+/**
+ * Store a value in task-local data. If this key already has a value,
+ * that value is overwritten (and its destructor is run).
+ */
+unsafe fn local_data_set<T: Owned>(
+    key: LocalDataKey<T>, +data: @T) {
+
+    local_set(rustrt::rust_get_task(), key, data)
+}
+/**
+ * Modify a task-local data value. If the function returns 'None', the
+ * data is removed (and its reference dropped).
+ */
+unsafe fn local_data_modify<T: Owned>(
+    key: LocalDataKey<T>,
+    modify_fn: fn(Option<@T>) -> Option<@T>) {
+
+    local_modify(rustrt::rust_get_task(), key, modify_fn)
+}
+
+#[test]
+fn test_tls_multitask() unsafe {
+    fn my_key(+_x: @~str) { }
+    local_data_set(my_key, @~"parent data");
+    do task::spawn unsafe {
+        assert local_data_get(my_key).is_none(); // TLS shouldn't carry over.
+        local_data_set(my_key, @~"child data");
+        assert *(local_data_get(my_key).get()) == ~"child data";
+        // should be cleaned up for us
+    }
+    // Must work multiple times
+    assert *(local_data_get(my_key).get()) == ~"parent data";
+    assert *(local_data_get(my_key).get()) == ~"parent data";
+    assert *(local_data_get(my_key).get()) == ~"parent data";
+}
+
+#[test]
+fn test_tls_overwrite() unsafe {
+    fn my_key(+_x: @~str) { }
+    local_data_set(my_key, @~"first data");
+    local_data_set(my_key, @~"next data"); // Shouldn't leak.
+    assert *(local_data_get(my_key).get()) == ~"next data";
+}
+
+#[test]
+fn test_tls_pop() unsafe {
+    fn my_key(+_x: @~str) { }
+    local_data_set(my_key, @~"weasel");
+    assert *(local_data_pop(my_key).get()) == ~"weasel";
+    // Pop must remove the data from the map.
+    assert local_data_pop(my_key).is_none();
+}
+
+#[test]
+fn test_tls_modify() unsafe {
+    fn my_key(+_x: @~str) { }
+    local_data_modify(my_key, |data| {
+        match data {
+            Some(@val) => fail ~"unwelcome value: " + val,
+            None       => Some(@~"first data")
+        }
+    });
+    local_data_modify(my_key, |data| {
+        match data {
+            Some(@~"first data") => Some(@~"next data"),
+            Some(@val)           => fail ~"wrong value: " + val,
+            None                 => fail ~"missing value"
+        }
+    });
+    assert *(local_data_pop(my_key).get()) == ~"next data";
+}
+
+#[test]
+fn test_tls_crust_automorestack_memorial_bug() unsafe {
+    // This might result in a stack-canary clobber if the runtime fails to set
+    // sp_limit to 0 when calling the cleanup extern - it might automatically
+    // jump over to the rust stack, which causes next_c_sp to get recorded as
+    // Something within a rust stack segment. Then a subsequent upcall (esp.
+    // for logging, think vsnprintf) would run on a stack smaller than 1 MB.
+    fn my_key(+_x: @~str) { }
+    do task::spawn {
+        unsafe { local_data_set(my_key, @~"hax"); }
+    }
+}
+
+#[test]
+fn test_tls_multiple_types() unsafe {
+    fn str_key(+_x: @~str) { }
+    fn box_key(+_x: @@()) { }
+    fn int_key(+_x: @int) { }
+    do task::spawn unsafe {
+        local_data_set(str_key, @~"string data");
+        local_data_set(box_key, @@());
+        local_data_set(int_key, @42);
+    }
+}
+
+#[test]
+fn test_tls_overwrite_multiple_types() {
+    fn str_key(+_x: @~str) { }
+    fn box_key(+_x: @@()) { }
+    fn int_key(+_x: @int) { }
+    do task::spawn unsafe {
+        local_data_set(str_key, @~"string data");
+        local_data_set(int_key, @42);
+        // This could cause a segfault if overwriting-destruction is done with
+        // the crazy polymorphic transmute rather than the provided finaliser.
+        local_data_set(int_key, @31337);
+    }
+}
+
+#[test]
+#[should_fail]
+#[ignore(cfg(windows))]
+fn test_tls_cleanup_on_failure() unsafe {
+    fn str_key(+_x: @~str) { }
+    fn box_key(+_x: @@()) { }
+    fn int_key(+_x: @int) { }
+    local_data_set(str_key, @~"parent data");
+    local_data_set(box_key, @@());
+    do task::spawn unsafe { // spawn_linked
+        local_data_set(str_key, @~"string data");
+        local_data_set(box_key, @@());
+        local_data_set(int_key, @42);
+        fail;
+    }
+    // Not quite nondeterministic.
+    local_data_set(int_key, @31337);
+    fail;
+}