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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] [PATCH 08/11] libxl: Asynchronous/long-running operation infrastructure
Provide a new set of machinery for writing public libxl functions
which may take a long time. The application gets to decide whether
they want the function to be synchronous, or whether they'd prefer to
get a callback, or an event, when the operation is complete.
User(s) of this machinery will be introduced in later patch(es).
Signed-off-by: Ian Jackson <ian.jackson@xxxxxxxxxxxxx>
---
tools/libxl/libxl.h | 53 ++++++++++++
tools/libxl/libxl_event.c | 188 ++++++++++++++++++++++++++++++++++++++++++
tools/libxl/libxl_internal.h | 107 ++++++++++++++++++++++++
tools/libxl/libxl_types.idl | 4 +
4 files changed, 352 insertions(+), 0 deletions(-)
diff --git a/tools/libxl/libxl.h b/tools/libxl/libxl.h
index e32881b..fa79c24 100644
--- a/tools/libxl/libxl.h
+++ b/tools/libxl/libxl.h
@@ -237,6 +237,59 @@ enum {
ERROR_BUFFERFULL = -13,
};
+
+/*
+ * Some libxl operations can take a long time. These functions take a
+ * parameter to control their concurrency:
+ * libxl_asyncop_how *ao_how
+ *
+ * If ao_how==NULL, the function will be synchronous.
+ *
+ * If ao_how!=NULL, the function will set the operation going, and if
+ * this is successful will return 0. In this case the zero error
+ * response does NOT mean that the operation was successful; it just
+ * means that it has been successfully started. It will finish later,
+ * perhaps with an error.
+ *
+ * If ao_how->callback!=NULL, the callback will be called when the
+ * operation completes. The same rules as for libxl_event_hooks
+ * apply, including the reentrancy rules and the possibility of
+ * "disaster", except that libxl calls ao_how->callback instead of
+ * libxl_event_hooks.event_occurs. (See libxl_event.h.)
+ *
+ * If ao_how->callback==NULL, a libxl_event will be generated which
+ * can be obtained from libxl_event_wait or libxl_event_check. The
+ * event will have type OPERATION_COMPLETE (which is not used
+ * elsewhere).
+ *
+ * Note that it is possible for an asynchronous operation which is to
+ * result in a callback to complete during its initiating function
+ * call. In this case the initiating function will return 0
+ * indicating the at the operation is "in progress", even though by
+ * the time it returns the operation is complete and the callback has
+ * already happened.
+ *
+ * The application must set and use ao_how->for_event (which will be
+ * copied into libxl_event.for_user) or ao_how->for_callback (passed
+ * to the callback) to determine which operation finished, and it must
+ * of course check the rc value for errors.
+ *
+ * *ao_how does not need to remain valid after the initiating function
+ * returns.
+ *
+ * Callbacks may occur on any thread in which the application calls
+ * libxl.
+ */
+
+typedef struct {
+ void (*callback)(libxl_ctx *ctx, int rc, void *for_callback);
+ union {
+ libxl_ev_user for_event; /* used if callback==NULL */
+ void *for_callback; /* passed to callback */
+ } u;
+} libxl_asyncop_how;
+
+
#define LIBXL_VERSION 0
typedef struct {
diff --git a/tools/libxl/libxl_event.c b/tools/libxl/libxl_event.c
index 73dfd9d..9e1ab56 100644
--- a/tools/libxl/libxl_event.c
+++ b/tools/libxl/libxl_event.c
@@ -771,10 +771,21 @@ static void egc_run_callbacks(libxl__egc *egc)
{
EGC_GC;
libxl_event *ev, *ev_tmp;
+
LIBXL_TAILQ_FOREACH_SAFE(ev, &egc->occurred_for_callback, link, ev_tmp) {
LIBXL_TAILQ_REMOVE(&egc->occurred_for_callback, ev, link);
CTX->event_hooks->event_occurs(CTX->event_hooks_user, ev);
}
+
+ libxl__ao *ao, *ao_tmp;
+ LIBXL_TAILQ_FOREACH_SAFE(ao, &egc->aos_for_callback,
+ entry_for_callback, ao_tmp) {
+ LIBXL_TAILQ_REMOVE(&egc->aos_for_callback, ao, entry_for_callback);
+ ao->how.callback(CTX, ao->rc, ao->how.u.for_callback);
+ ao->notified = 1;
+ if (!ao->in_initiator)
+ libxl__ao__destroy(CTX, ao);
+ }
}
void libxl__egc_cleanup(libxl__egc *egc)
@@ -1061,6 +1072,183 @@ int libxl_event_wait(libxl_ctx *ctx, libxl_event
**event_r,
return rc;
}
+
+
+/*
+ * The two possible state flow of an ao:
+ *
+ * Completion before initiator return:
+ *
+ * Initiator thread Possible other threads
+ *
+ * * ao_create allocates memory and
+ * initialises the struct
+ *
+ * * the initiator function does its
+ * work, setting up various internal
+ * asynchronous operations -----------> * asynchronous operations
+ * start to take place and
+ * might cause ao completion
+ * |
+ * * initiator calls ao_inprogress |
+ * - if synchronous, run event loop |
+ * until the ao completes |
+ * - ao completes on some thread
+ * - completing thread releases the lock
+ * <--------------'
+ * - ao_inprogress takes the lock
+ * - destroy the ao
+ *
+ *
+ * Completion after initiator return (asynch. only):
+ *
+ *
+ * Initiator thread Possible other threads
+ *
+ * * ao_create allocates memory and
+ * initialises the struct
+ *
+ * * the initiator function does its
+ * work, setting up various internal
+ * asynchronous operations -----------> * asynchronous operations
+ * start to take place and
+ * might cause ao completion
+ * |
+ * * initiator calls ao_inprogress |
+ * - observes event not yet done, |
+ * - returns to caller |
+ * |
+ * - ao completes on some thread
+ * - generate the event or call the callback
+ * - destroy the ao
+ */
+
+void libxl__ao__destroy(libxl_ctx *ctx, libxl__ao *ao)
+{
+ if (!ao) return;
+ if (ao->poller) libxl__poller_put(ctx, ao->poller);
+ ao->magic = LIBXL__AO_MAGIC_DESTROYED;
+ libxl__free_all(&ao->gc);
+ free(ao);
+}
+
+void libxl__ao_abort(libxl__ao *ao)
+{
+ AO_GC;
+ assert(ao->magic == LIBXL__AO_MAGIC);
+ assert(ao->in_initiator);
+ assert(!ao->complete);
+ libxl__ao__destroy(CTX, ao);
+}
+
+void libxl__ao_complete(libxl__egc *egc, libxl__ao *ao, int rc)
+{
+ assert(ao->magic == LIBXL__AO_MAGIC);
+ assert(!ao->complete);
+ ao->complete = 1;
+ ao->rc = rc;
+
+ if (ao->poller) {
+ assert(ao->in_initiator);
+ libxl__poller_wakeup(egc, ao->poller);
+ } else if (ao->how.callback) {
+ LIBXL_TAILQ_INSERT_TAIL(&egc->aos_for_callback, ao,
entry_for_callback);
+ } else {
+ libxl_event *ev;
+ ev = NEW_EVENT(egc, OPERATION_COMPLETE, ao->domid);
+ if (ev) {
+ ev->for_user = ao->how.u.for_event;
+ ev->u.operation_complete.rc = ao->rc;
+ libxl__event_occurred(egc, ev);
+ }
+ ao->notified = 1;
+ }
+ if (!ao->in_initiator && ao->notified)
+ libxl__ao__destroy(libxl__gc_owner(&egc->gc), ao);
+}
+
+libxl__ao *libxl__ao_create(libxl_ctx *ctx, uint32_t domid,
+ const libxl_asyncop_how *how)
+{
+ libxl__ao *ao;
+
+ ao = calloc(1, sizeof(*ao));
+ if (!ao) goto out;
+
+ ao->magic = LIBXL__AO_MAGIC;
+ ao->in_initiator = 1;
+ ao->poller = 0;
+ ao->domid = domid;
+ LIBXL_INIT_GC(ao->gc, ctx);
+
+ if (how) {
+ ao->how = *how;
+ } else {
+ ao->poller = libxl__poller_get(ctx);
+ if (!ao->poller) goto out;
+ }
+ return ao;
+
+ out:
+ if (ao) libxl__ao__destroy(ctx, ao);
+ return NULL;
+}
+
+int libxl__ao_inprogress(libxl__ao *ao)
+{
+ AO_GC;
+ int rc;
+
+ assert(ao->magic == LIBXL__AO_MAGIC);
+ assert(ao->in_initiator);
+
+ if (ao->poller) {
+ /* Caller wants it done synchronously. */
+ /* We use a fresh gc, so that we can free things
+ * each time round the loop. */
+ libxl__egc egc;
+ LIBXL_INIT_EGC(egc,CTX);
+
+ for (;;) {
+ assert(ao->magic == LIBXL__AO_MAGIC);
+
+ if (ao->complete) {
+ rc = ao->rc;
+ ao->notified = 1;
+ break;
+ }
+
+ rc = eventloop_iteration(&egc,ao->poller);
+ if (rc) {
+ /* Oh dear, this is quite unfortunate. */
+ LIBXL__LOG(CTX, LIBXL__LOG_ERROR, "Error waiting for"
+ " event during long-running operation (rc=%d)", rc);
+ sleep(1);
+ /* It's either this or return ERROR_I_DONT_KNOW_WHETHER
+ * _THE_THING_YOU_ASKED_FOR_WILL_BE_DONE_LATER_WHEN
+ * _YOU_DIDNT_EXPECT_IT, since we don't have any kind of
+ * cancellation ability. */
+ }
+
+ CTX_UNLOCK;
+ libxl__egc_cleanup(&egc);
+ CTX_LOCK;
+ }
+ } else {
+ rc = 0;
+ }
+
+ ao->in_initiator = 0;
+
+ if (ao->notified) {
+ assert(ao->complete);
+ libxl__ao__destroy(CTX,ao);
+ }
+
+ return rc;
+}
+
+
/*
* Local variables:
* mode: C
diff --git a/tools/libxl/libxl_internal.h b/tools/libxl/libxl_internal.h
index d1b96c1..044eeb4 100644
--- a/tools/libxl/libxl_internal.h
+++ b/tools/libxl/libxl_internal.h
@@ -114,6 +114,7 @@ _hidden void libxl__log(libxl_ctx *ctx, xentoollog_level
msglevel, int errnoval,
typedef struct libxl__gc libxl__gc;
typedef struct libxl__egc libxl__egc;
+typedef struct libxl__ao libxl__ao;
typedef struct libxl__ev_fd libxl__ev_fd;
typedef void libxl__ev_fd_callback(libxl__egc *egc, libxl__ev_fd *ev,
@@ -218,6 +219,10 @@ struct libxl__poller {
* releasing the ctx lock and going into poll; when it comes out
* of poll it will take the poller off the pollers_event list.
*
+ * A thread which is waiting for completion of a synchronous ao
+ * will allocate a poller and record it in the ao, so that other
+ * threads can wake it up.
+ *
* When a thread is done with a poller it should put it onto
* pollers_idle, where it can be reused later.
*
@@ -324,6 +329,21 @@ struct libxl__egc {
/* for event-generating functions only */
struct libxl__gc gc;
struct libxl__event_list occurred_for_callback;
+ LIBXL_TAILQ_HEAD(, libxl__ao) aos_for_callback;
+};
+
+#define LIBXL__AO_MAGIC 0xA0FACE00ul
+#define LIBXL__AO_MAGIC_DESTROYED 0xA0DEAD00ul
+
+struct libxl__ao {
+ uint32_t magic;
+ unsigned in_initiator:1, complete:1, notified:1;
+ int rc;
+ libxl__gc gc;
+ libxl_asyncop_how how;
+ libxl__poller *poller;
+ uint32_t domid;
+ LIBXL_TAILQ_ENTRY(libxl__ao) entry_for_callback;
};
#define LIBXL_INIT_GC(gc,ctx) do{ \
@@ -1108,6 +1128,7 @@ libxl__device_model_version_running(libxl__gc *gc,
uint32_t domid);
#define LIBXL_INIT_EGC(egc,ctx) do{ \
LIBXL_INIT_GC((egc).gc,ctx); \
LIBXL_TAILQ_INIT(&(egc).occurred_for_callback); \
+ LIBXL_TAILQ_INIT(&(egc).aos_for_callback); \
} while(0)
_hidden void libxl__egc_cleanup(libxl__egc *egc);
@@ -1125,6 +1146,92 @@ _hidden void libxl__egc_cleanup(libxl__egc *egc);
/*
+ * Machinery for asynchronous operations ("ao")
+ *
+ * All "slow" functions (includes anything that might block on a
+ * guest or an external script) need to use the asynchronous
+ * operation ("ao") machinery. The function should take a parameter
+ * const libxl_asyncop_how *ao_how and must start with a call to
+ * AO_INITIATOR_ENTRY. These functions MAY NOT be called from
+ * outside libxl, because they can cause reentrancy callbacks.
+ *
+ * Lifecycle of an ao:
+ *
+ * - Created by libxl__ao_create (or the AO_CREATE convenience macro).
+ *
+ * - After creation, can be used by code which implements
+ * the operation as follows:
+ * - the ao's gc, for allocating memory for the lifetime
+ * of the operation (possibly with the help of the AO_GC
+ * macro to introduce the gc into scope)
+ * - the ao itself may be passed about to sub-functions
+ * so that they can stash it away etc.
+ * - in particular, the ao pointer must be stashed in some
+ * per-operation structure which is also passed as a user
+ * pointer to the internal event generation request routines
+ * libxl__evgen_FOO, so that at some point a CALLBACK will be
+ * made when the operation is complete.
+ *
+ * - If initiation is successful, the initiating function needs
+ * to run libxl__ao_inprogress right before unlocking and
+ * returning, and return whatever it returns (AO_INPROGRESS macro).
+ *
+ * - If the initiation is unsuccessful, the initiating function must
+ * call libxl__ao_abort before unlocking and returning whatever
+ * error code is appropriate (AO_ABORT macro).
+ *
+ * - Later, some callback function, whose callback has been requested
+ * directly or indirectly, should call libxl__ao_complete (with the
+ * ctx locked, as it will generally already be in any event callback
+ * function). This must happen exactly once for each ao (and not if
+ * the ao has been destroyed, obviously), and it may not happen
+ * until libxl__ao_inprogress has been called on the ao.
+ *
+ * - Note that during callback functions, two gcs are available:
+ * - The one in egc, whose lifetime is only this callback
+ * - The one in ao, whose lifetime is the asynchronous operation
+ * Usually callback function should use CONTAINER_OF
+ * to obtain its own structure, containing a pointer to the ao,
+ * and then use the gc from that ao.
+ */
+
+#define AO_CREATE(ctx, domid, ao_how) \
+ libxl__ctx_lock(ctx); \
+ libxl__ao *ao = libxl__ao_create(ctx, domid, ao_how); \
+ if (!ao) { libxl__ctx_unlock(ctx); return ERROR_NOMEM; } \
+ AO_GC;
+
+#define AO_INPROGRESS ({ \
+ libxl_ctx *ao__ctx = libxl__gc_owner(&ao->gc); \
+ int ao__rc = libxl__ao_inprogress(ao); \
+ libxl__ctx_unlock(ao__ctx); /* gc is now invalid */ \
+ (ao__rc); \
+ })
+
+#define AO_ABORT(rc) ({ \
+ libxl_ctx *ao__ctx = libxl__gc_owner(&ao->gc); \
+ assert(rc); \
+ libxl__ao_abort(ao); \
+ libxl__ctx_unlock(ao__ctx); /* gc is now invalid */ \
+ (rc); \
+ })
+
+#define AO_GC \
+ libxl__gc *const gc = &ao->gc
+
+
+/* All of these MUST be called with the ctx locked.
+ * libxl__ao_inprogress MUST be called with the ctx locked exactly once. */
+_hidden libxl__ao *libxl__ao_create(libxl_ctx*, uint32_t domid,
+ const libxl_asyncop_how*);
+_hidden int libxl__ao_inprogress(libxl__ao *ao);
+_hidden void libxl__ao_abort(libxl__ao *ao);
+_hidden void libxl__ao_complete(libxl__egc *egc, libxl__ao *ao, int rc);
+
+/* For use by ao machinery ONLY */
+_hidden void libxl__ao__destroy(libxl_ctx*, libxl__ao *ao);
+
+/*
* Convenience macros.
*/
diff --git a/tools/libxl/libxl_types.idl b/tools/libxl/libxl_types.idl
index 35b53d6..8871c17 100644
--- a/tools/libxl/libxl_types.idl
+++ b/tools/libxl/libxl_types.idl
@@ -395,6 +395,7 @@ libxl_event_type = Enumeration("event_type", [
(1, "DOMAIN_SHUTDOWN"),
(2, "DOMAIN_DESTROY"),
(3, "DISK_EJECT"),
+ (4, "OPERATION_COMPLETE"),
])
libxl_ev_user = UInt(64)
@@ -418,4 +419,7 @@ libxl_event = Struct("event",[
("vdev", string),
("disk", libxl_device_disk),
])),
+ ("operation_complete", Struct(None, [
+ ("rc", integer),
+ ])),
]))])
--
1.7.2.5
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