Merge pull request #1758 from dgquintas/iomgr_managed_cbs

Revamped iomgr's callback mechanism

src/core/channel/child_channel.c

@@ -58,6 +58,9 @@ typedef struct {
   gpr_uint8 sending_farewell;
   /* have we sent farewell (goaway + disconnect) */
   gpr_uint8 sent_farewell;
+
+  grpc_iomgr_closure finally_destroy_channel_closure;
+  grpc_iomgr_closure send_farewells_closure;
 } lb_channel_data;
 
 typedef struct { grpc_child_channel *channel; } lb_call_data;
@@ -213,12 +216,16 @@ static void maybe_destroy_channel(grpc_child_channel *channel) {
   lb_channel_data *chand = LINK_BACK_ELEM_FROM_CHANNEL(channel)->channel_data;
   if (chand->destroyed && chand->disconnected && chand->active_calls == 0 &&
       !chand->sending_farewell && !chand->calling_back) {
-    grpc_iomgr_add_callback(finally_destroy_channel, channel);
+    chand->finally_destroy_channel_closure.cb = finally_destroy_channel;
+    chand->finally_destroy_channel_closure.cb_arg = channel;
+    grpc_iomgr_add_callback(&chand->finally_destroy_channel_closure);
   } else if (chand->destroyed && !chand->disconnected &&
              chand->active_calls == 0 && !chand->sending_farewell &&
              !chand->sent_farewell) {
     chand->sending_farewell = 1;
-    grpc_iomgr_add_callback(send_farewells, channel);
+    chand->send_farewells_closure.cb = send_farewells;
+    chand->send_farewells_closure.cb_arg = channel;
+    grpc_iomgr_add_callback(&chand->send_farewells_closure);
   }
 }
 

src/core/iomgr/fd_posix.c

@@ -91,6 +91,7 @@ static grpc_fd *alloc_fd(int fd) {
     gpr_mu_init(&r->set_state_mu);
     gpr_mu_init(&r->watcher_mu);
   }
+
   gpr_atm_rel_store(&r->refst, 1);
   gpr_atm_rel_store(&r->readst, NOT_READY);
   gpr_atm_rel_store(&r->writest, NOT_READY);
@@ -116,8 +117,7 @@ static void ref_by(grpc_fd *fd, int n) {
 static void unref_by(grpc_fd *fd, int n) {
   gpr_atm old = gpr_atm_full_fetch_add(&fd->refst, -n);
   if (old == n) {
-    close(fd->fd);
-    grpc_iomgr_add_callback(fd->on_done, fd->on_done_user_data);
+    grpc_iomgr_add_callback(&fd->on_done_closure);
     freelist_fd(fd);
     grpc_iomgr_unref();
   } else {
@@ -180,8 +180,8 @@ static void wake_all_watchers_locked(grpc_fd *fd) {
 }
 
 void grpc_fd_orphan(grpc_fd *fd, grpc_iomgr_cb_func on_done, void *user_data) {
-  fd->on_done = on_done ? on_done : do_nothing;
-  fd->on_done_user_data = user_data;
+  grpc_iomgr_closure_init(&fd->on_done_closure, on_done ? on_done : do_nothing,
+                          user_data);
   shutdown(fd->fd, SHUT_RDWR);
   ref_by(fd, 1); /* remove active status, but keep referenced */
   gpr_mu_lock(&fd->watcher_mu);
@@ -195,21 +195,20 @@ void grpc_fd_ref(grpc_fd *fd) { ref_by(fd, 2); }
 
 void grpc_fd_unref(grpc_fd *fd) { unref_by(fd, 2); }
 
-static void make_callback(grpc_iomgr_cb_func cb, void *arg, int success,
+static void process_callback(grpc_iomgr_closure *closure, int success,
                           int allow_synchronous_callback) {
   if (allow_synchronous_callback) {
-    cb(arg, success);
+    closure->cb(closure->cb_arg, success);
   } else {
-    grpc_iomgr_add_delayed_callback(cb, arg, success);
+    grpc_iomgr_add_delayed_callback(closure, success);
   }
 }
 
-static void make_callbacks(grpc_iomgr_closure *callbacks, size_t n, int success,
-                           int allow_synchronous_callback) {
+static void process_callbacks(grpc_iomgr_closure *callbacks, size_t n,
+                              int success, int allow_synchronous_callback) {
   size_t i;
   for (i = 0; i < n; i++) {
-    make_callback(callbacks[i].cb, callbacks[i].cb_arg, success,
-                  allow_synchronous_callback);
+    process_callback(callbacks + i, success, allow_synchronous_callback);
   }
 }
 
@@ -234,10 +233,9 @@ static void notify_on(grpc_fd *fd, gpr_atm *st, grpc_iomgr_closure *closure,
     /* swap was unsuccessful due to an intervening set_ready call.
        Fall through to the READY code below */
     case READY:
-      assert(gpr_atm_no_barrier_load(st) == READY);
+      GPR_ASSERT(gpr_atm_no_barrier_load(st) == READY);
       gpr_atm_rel_store(st, NOT_READY);
-      make_callback(closure->cb, closure->cb_arg,
-                    !gpr_atm_acq_load(&fd->shutdown),
+      process_callback(closure, !gpr_atm_acq_load(&fd->shutdown),
                     allow_synchronous_callback);
       return;
     default: /* WAITING */
@@ -251,7 +249,7 @@ static void notify_on(grpc_fd *fd, gpr_atm *st, grpc_iomgr_closure *closure,
   abort();
 }
 
-static void set_ready_locked(gpr_atm *st, grpc_iomgr_closure *callbacks,
+static void set_ready_locked(gpr_atm *st, grpc_iomgr_closure **callbacks,
                              size_t *ncallbacks) {
   gpr_intptr state = gpr_atm_acq_load(st);
 
@@ -269,9 +267,9 @@ static void set_ready_locked(gpr_atm *st, grpc_iomgr_closure *callbacks,
          Fall through to the WAITING code below */
       state = gpr_atm_acq_load(st);
     default: /* waiting */
-      assert(gpr_atm_no_barrier_load(st) != READY &&
-             gpr_atm_no_barrier_load(st) != NOT_READY);
-      callbacks[(*ncallbacks)++] = *(grpc_iomgr_closure *)state;
+      GPR_ASSERT(gpr_atm_no_barrier_load(st) != READY &&
+                 gpr_atm_no_barrier_load(st) != NOT_READY);
+      callbacks[(*ncallbacks)++] = (grpc_iomgr_closure *)state;
       gpr_atm_rel_store(st, NOT_READY);
       return;
   }
@@ -282,25 +280,30 @@ static void set_ready(grpc_fd *fd, gpr_atm *st,
   /* only one set_ready can be active at once (but there may be a racing
      notify_on) */
   int success;
-  grpc_iomgr_closure cb;
+  grpc_iomgr_closure* closure;
   size_t ncb = 0;
+
   gpr_mu_lock(&fd->set_state_mu);
-  set_ready_locked(st, &cb, &ncb);
+  set_ready_locked(st, &closure, &ncb);
   gpr_mu_unlock(&fd->set_state_mu);
   success = !gpr_atm_acq_load(&fd->shutdown);
-  make_callbacks(&cb, ncb, success, allow_synchronous_callback);
+  GPR_ASSERT(ncb <= 1);
+  if (ncb > 0) {
+    process_callbacks(closure, ncb, success, allow_synchronous_callback);
+  }
 }
 
 void grpc_fd_shutdown(grpc_fd *fd) {
-  grpc_iomgr_closure cb[2];
   size_t ncb = 0;
   gpr_mu_lock(&fd->set_state_mu);
   GPR_ASSERT(!gpr_atm_no_barrier_load(&fd->shutdown));
   gpr_atm_rel_store(&fd->shutdown, 1);
-  set_ready_locked(&fd->readst, cb, &ncb);
-  set_ready_locked(&fd->writest, cb, &ncb);
+  set_ready_locked(&fd->readst, &fd->shutdown_closures[0], &ncb);
+  set_ready_locked(&fd->writest, &fd->shutdown_closures[0], &ncb);
   gpr_mu_unlock(&fd->set_state_mu);
-  make_callbacks(cb, ncb, 0, 0);
+  GPR_ASSERT(ncb <= 2);
+  process_callbacks(fd->shutdown_closures[0], ncb, 0 /* GPR_FALSE */,
+                    0 /* GPR_FALSE */);
 }
 
 void grpc_fd_notify_on_read(grpc_fd *fd, grpc_iomgr_closure *closure) {

src/core/iomgr/fd_posix.h

@@ -40,11 +40,6 @@
 #include <grpc/support/sync.h>
 #include <grpc/support/time.h>
 
-typedef struct {
-  grpc_iomgr_cb_func cb;
-  void *cb_arg;
-} grpc_iomgr_closure;
-
 typedef struct grpc_fd grpc_fd;
 
 typedef struct grpc_fd_watcher {
@@ -96,9 +91,10 @@ struct grpc_fd {
   gpr_atm readst;
   gpr_atm writest;
 
-  grpc_iomgr_cb_func on_done;
-  void *on_done_user_data;
   struct grpc_fd *freelist_next;
+
+  grpc_iomgr_closure on_done_closure;
+  grpc_iomgr_closure *shutdown_closures[2];
 };
 
 /* Create a wrapped file descriptor.

src/core/iomgr/iomgr.c

@@ -42,17 +42,10 @@
 #include <grpc/support/thd.h>
 #include <grpc/support/sync.h>
 
-typedef struct delayed_callback {
-  grpc_iomgr_cb_func cb;
-  void *cb_arg;
-  int success;
-  struct delayed_callback *next;
-} delayed_callback;
-
 static gpr_mu g_mu;
 static gpr_cv g_rcv;
-static delayed_callback *g_cbs_head = NULL;
-static delayed_callback *g_cbs_tail = NULL;
+static grpc_iomgr_closure *g_cbs_head = NULL;
+static grpc_iomgr_closure *g_cbs_tail = NULL;
 static int g_shutdown;
 static int g_refs;
 static gpr_event g_background_callback_executor_done;
@@ -66,12 +59,11 @@ static void background_callback_executor(void *ignored) {
     gpr_timespec short_deadline =
         gpr_time_add(gpr_now(), gpr_time_from_millis(100));
     if (g_cbs_head) {
-      delayed_callback *cb = g_cbs_head;
-      g_cbs_head = cb->next;
+      grpc_iomgr_closure *closure = g_cbs_head;
+      g_cbs_head = closure->next;
       if (!g_cbs_head) g_cbs_tail = NULL;
       gpr_mu_unlock(&g_mu);
-      cb->cb(cb->cb_arg, cb->success);
-      gpr_free(cb);
+      closure->cb(closure->cb_arg, closure->success);
       gpr_mu_lock(&g_mu);
     } else if (grpc_alarm_check(&g_mu, gpr_now(), &deadline)) {
     } else {
@@ -103,7 +95,7 @@ void grpc_iomgr_init(void) {
 }
 
 void grpc_iomgr_shutdown(void) {
-  delayed_callback *cb;
+  grpc_iomgr_closure *closure;
   gpr_timespec shutdown_deadline =
       gpr_time_add(gpr_now(), gpr_time_from_seconds(10));
 
@@ -114,13 +106,12 @@ void grpc_iomgr_shutdown(void) {
     gpr_log(GPR_DEBUG, "Waiting for %d iomgr objects to be destroyed%s", g_refs,
             g_cbs_head ? " and executing final callbacks" : "");
     while (g_cbs_head) {
-      cb = g_cbs_head;
-      g_cbs_head = cb->next;
+      closure = g_cbs_head;
+      g_cbs_head = closure->next;
       if (!g_cbs_head) g_cbs_tail = NULL;
       gpr_mu_unlock(&g_mu);
 
-      cb->cb(cb->cb_arg, 0);
-      gpr_free(cb);
+      closure->cb(closure->cb_arg, 0);
       gpr_mu_lock(&g_mu);
     }
     if (g_refs) {
@@ -167,42 +158,48 @@ void grpc_iomgr_unref(void) {
   gpr_mu_unlock(&g_mu);
 }
 
-void grpc_iomgr_add_delayed_callback(grpc_iomgr_cb_func cb, void *cb_arg,
-                                     int success) {
-  delayed_callback *dcb = gpr_malloc(sizeof(delayed_callback));
-  dcb->cb = cb;
-  dcb->cb_arg = cb_arg;
-  dcb->success = success;
+
+void grpc_iomgr_closure_init(grpc_iomgr_closure *closure, grpc_iomgr_cb_func cb,
+                             void *cb_arg) {
+  closure->cb = cb;
+  closure->cb_arg = cb_arg;
+  closure->next = NULL;
+}
+
+void grpc_iomgr_add_delayed_callback(grpc_iomgr_closure *closure, int success) {
+  closure->success = success;
   gpr_mu_lock(&g_mu);
-  dcb->next = NULL;
+  closure->next = NULL;
   if (!g_cbs_tail) {
-    g_cbs_head = g_cbs_tail = dcb;
+    g_cbs_head = g_cbs_tail = closure;
   } else {
-    g_cbs_tail->next = dcb;
-    g_cbs_tail = dcb;
+    g_cbs_tail->next = closure;
+    g_cbs_tail = closure;
   }
   gpr_mu_unlock(&g_mu);
 }
 
-void grpc_iomgr_add_callback(grpc_iomgr_cb_func cb, void *cb_arg) {
-  grpc_iomgr_add_delayed_callback(cb, cb_arg, 1);
+
+void grpc_iomgr_add_callback(grpc_iomgr_closure *closure) {
+  grpc_iomgr_add_delayed_callback(closure, 1 /* GPR_TRUE */);
 }
 
+
 int grpc_maybe_call_delayed_callbacks(gpr_mu *drop_mu, int success) {
   int n = 0;
   gpr_mu *retake_mu = NULL;
-  delayed_callback *cb;
+  grpc_iomgr_closure *closure;
   for (;;) {
     /* check for new work */
     if (!gpr_mu_trylock(&g_mu)) {
       break;
     }
-    cb = g_cbs_head;
-    if (!cb) {
+    closure = g_cbs_head;
+    if (!closure) {
       gpr_mu_unlock(&g_mu);
       break;
     }
-    g_cbs_head = cb->next;
+    g_cbs_head = closure->next;
     if (!g_cbs_head) g_cbs_tail = NULL;
     gpr_mu_unlock(&g_mu);
     /* if we have a mutex to drop, do so before executing work */
@@ -211,8 +208,7 @@ int grpc_maybe_call_delayed_callbacks(gpr_mu *drop_mu, int success) {
       retake_mu = drop_mu;
       drop_mu = NULL;
     }
-    cb->cb(cb->cb_arg, success && cb->success);
-    gpr_free(cb);
+    closure->cb(closure->cb_arg, success && closure->success);
     n++;
   }
   if (retake_mu) {

src/core/iomgr/iomgr.h

@@ -34,14 +34,43 @@
 #ifndef GRPC_INTERNAL_CORE_IOMGR_IOMGR_H
 #define GRPC_INTERNAL_CORE_IOMGR_IOMGR_H
 
-/* gRPC Callback definition */
+/** gRPC Callback definition.
+ *
+ * \param arg Arbitrary input.
+ * \param success An indication on the state of the iomgr. On false, cleanup
+ * actions should be taken (eg, shutdown). */
 typedef void (*grpc_iomgr_cb_func)(void *arg, int success);
 
+/** A closure over a grpc_iomgr_cb_func. */
+typedef struct grpc_iomgr_closure {
+  /** Bound callback. */
+  grpc_iomgr_cb_func cb;
+
+  /** Arguments to be passed to "cb". */
+  void *cb_arg;
+
+  /** Internal. A boolean indication to "cb" on the state of the iomgr.
+   * For instance, closures created during a shutdown would have this field set
+   * to false. */
+  int success;
+
+  /**< Internal. Do not touch */
+  struct grpc_iomgr_closure *next;
+} grpc_iomgr_closure;
+
+/** Initializes \a closure with \a cb and \a cb_arg. */
+void grpc_iomgr_closure_init(grpc_iomgr_closure *closure, grpc_iomgr_cb_func cb,
+                             void *cb_arg);
+
+/** Initializes the iomgr. */
 void grpc_iomgr_init(void);
+
+/** Signals the intention to shutdown the iomgr. */
 void grpc_iomgr_shutdown(void);
 
-/* This function is called from within a callback or from anywhere else
-   and causes the invocation of a callback at some point in the future */
-void grpc_iomgr_add_callback(grpc_iomgr_cb_func cb, void *cb_arg);
+/** Registers a closure to be invoked at some point in the future.
+ *
+ * Can be called from within a callback or from anywhere else */
+void grpc_iomgr_add_callback(grpc_iomgr_closure *closure);
 
 #endif  /* GRPC_INTERNAL_CORE_IOMGR_IOMGR_H */

src/core/iomgr/iomgr_internal.h

@@ -35,12 +35,10 @@
 #define GRPC_INTERNAL_CORE_IOMGR_IOMGR_INTERNAL_H
 
 #include "src/core/iomgr/iomgr.h"
-#include "src/core/iomgr/iomgr_internal.h"
 #include <grpc/support/sync.h>
 
 int grpc_maybe_call_delayed_callbacks(gpr_mu *drop_mu, int success);
-void grpc_iomgr_add_delayed_callback(grpc_iomgr_cb_func cb, void *cb_arg,
-                                     int success);
+void grpc_iomgr_add_delayed_callback(grpc_iomgr_closure *iocb, int success);
 
 void grpc_iomgr_ref(void);
 void grpc_iomgr_unref(void);

src/core/iomgr/pollset_posix.c

@@ -257,6 +257,7 @@ typedef struct grpc_unary_promote_args {
   const grpc_pollset_vtable *original_vtable;
   grpc_pollset *pollset;
   grpc_fd *fd;
+  grpc_iomgr_closure promotion_closure;
 } grpc_unary_promote_args;
 
 static void unary_poll_do_promote(void *args, int success) {
@@ -279,7 +280,7 @@ static void unary_poll_do_promote(void *args, int success) {
   /* First we need to ensure that nobody is polling concurrently */
   while (pollset->counter != 0) {
     grpc_pollset_kick(pollset);
-    grpc_iomgr_add_callback(unary_poll_do_promote, up_args);
+    grpc_iomgr_add_callback(&up_args->promotion_closure);
     gpr_mu_unlock(&pollset->mu);
     return;
   }
@@ -363,7 +364,9 @@ static void unary_poll_pollset_add_fd(grpc_pollset *pollset, grpc_fd *fd) {
   up_args->pollset = pollset;
   up_args->fd = fd;
   up_args->original_vtable = pollset->vtable;
-  grpc_iomgr_add_callback(unary_poll_do_promote, up_args);
+  up_args->promotion_closure.cb = unary_poll_do_promote;
+  up_args->promotion_closure.cb_arg = up_args;
+  grpc_iomgr_add_callback(&up_args->promotion_closure);
 
   grpc_pollset_kick(pollset);
 }

src/core/iomgr/pollset_windows.c

@@ -66,15 +66,15 @@ int grpc_pollset_work(grpc_pollset *pollset, gpr_timespec deadline) {
   gpr_timespec now;
   now = gpr_now();
   if (gpr_time_cmp(now, deadline) > 0) {
-    return 0;
+    return 0 /* GPR_FALSE */;
   }
-  if (grpc_maybe_call_delayed_callbacks(NULL, 1)) {
-    return 1;
+  if (grpc_maybe_call_delayed_callbacks(NULL, 1 /* GPR_TRUE */)) {
+    return 1 /* GPR_TRUE */;
   }
   if (grpc_alarm_check(NULL, now, &deadline)) {
-    return 1;
+    return 1 /* GPR_TRUE */;
   }
-  return 0;
+  return 0 /* GPR_FALSE */;
 }
 
 void grpc_pollset_kick(grpc_pollset *p) { }

src/core/iomgr/socket_windows.c

@@ -39,7 +39,6 @@
 #include <grpc/support/log.h>
 
 #include "src/core/iomgr/iocp_windows.h"
-#include "src/core/iomgr/iomgr.h"
 #include "src/core/iomgr/iomgr_internal.h"
 #include "src/core/iomgr/pollset.h"
 #include "src/core/iomgr/pollset_windows.h"
@@ -64,13 +63,15 @@ int grpc_winsocket_shutdown(grpc_winsocket *socket) {
   gpr_mu_lock(&socket->state_mu);
   if (socket->read_info.cb) {
     callbacks_set++;
-    grpc_iomgr_add_delayed_callback(socket->read_info.cb,
-                                    socket->read_info.opaque, 0);
+    grpc_iomgr_closure_init(&socket->shutdown_closure, socket->read_info.cb,
+                            socket->read_info.opaque);
+    grpc_iomgr_add_delayed_callback(&socket->shutdown_closure, 0);
   }
   if (socket->write_info.cb) {
     callbacks_set++;
-    grpc_iomgr_add_delayed_callback(socket->write_info.cb,
-                                    socket->write_info.opaque, 0);
+    grpc_iomgr_closure_init(&socket->shutdown_closure, socket->write_info.cb,
+                            socket->write_info.opaque);
+    grpc_iomgr_add_delayed_callback(&socket->shutdown_closure, 0);
   }
   gpr_mu_unlock(&socket->state_mu);
   return callbacks_set;

src/core/iomgr/socket_windows.h

@@ -39,6 +39,8 @@
 #include <grpc/support/sync.h>
 #include <grpc/support/atm.h>
 
+#include "src/core/iomgr/iomgr.h"
+
 /* This holds the data for an outstanding read or write on a socket.
    The mutex to protect the concurrent access to that data is the one
    inside the winsocket wrapper. */
@@ -93,6 +95,8 @@ typedef struct grpc_winsocket {
      there is a pending operation that the IO Completion Port will have to
      wait for. The socket will be collected at that time. */
   int orphan;
+
+  grpc_iomgr_closure shutdown_closure;
 } grpc_winsocket;
 
 /* Create a wrapped windows handle. This takes ownership of it, meaning that

src/core/iomgr/tcp_posix.c

@@ -280,6 +280,8 @@ typedef struct {
 
   grpc_iomgr_closure read_closure;
   grpc_iomgr_closure write_closure;
+
+  grpc_iomgr_closure handle_read_closure;
 } grpc_tcp;
 
 static void grpc_tcp_handle_read(void *arg /* grpc_tcp */, int success);
@@ -443,7 +445,8 @@ static void grpc_tcp_notify_on_read(grpc_endpoint *ep, grpc_endpoint_read_cb cb,
     tcp->finished_edge = 0;
     grpc_fd_notify_on_read(tcp->em_fd, &tcp->read_closure);
   } else {
-    grpc_iomgr_add_callback(grpc_tcp_handle_read, tcp);
+    tcp->handle_read_closure.cb_arg = tcp;
+    grpc_iomgr_add_callback(&tcp->handle_read_closure);
   }
 }
 
@@ -592,6 +595,8 @@ grpc_endpoint *grpc_tcp_create(grpc_fd *em_fd, size_t slice_size) {
   tcp->read_closure.cb_arg = tcp;
   tcp->write_closure.cb = grpc_tcp_handle_write;
   tcp->write_closure.cb_arg = tcp;
+
+  tcp->handle_read_closure.cb = grpc_tcp_handle_read;
   return &tcp->base;
 }
 

src/core/security/credentials.c

@@ -54,6 +54,7 @@
 typedef struct {
   grpc_credentials *creds;
   grpc_credentials_metadata_cb cb;
+  grpc_iomgr_closure *on_simulated_token_fetch_done_closure;
   void *user_data;
 } grpc_credentials_metadata_request;
 
@@ -65,6 +66,8 @@ grpc_credentials_metadata_request_create(grpc_credentials *creds,
       gpr_malloc(sizeof(grpc_credentials_metadata_request));
   r->creds = grpc_credentials_ref(creds);
   r->cb = cb;
+  r->on_simulated_token_fetch_done_closure =
+      gpr_malloc(sizeof(grpc_iomgr_closure));
   r->user_data = user_data;
   return r;
 }
@@ -72,6 +75,7 @@ grpc_credentials_metadata_request_create(grpc_credentials *creds,
 static void grpc_credentials_metadata_request_destroy(
     grpc_credentials_metadata_request *r) {
   grpc_credentials_unref(r->creds);
+  gpr_free(r->on_simulated_token_fetch_done_closure);
   gpr_free(r);
 }
 
@@ -831,9 +835,11 @@ static void fake_oauth2_get_request_metadata(grpc_credentials *creds,
   grpc_fake_oauth2_credentials *c = (grpc_fake_oauth2_credentials *)creds;
 
   if (c->is_async) {
-    grpc_iomgr_add_callback(
-        on_simulated_token_fetch_done,
-        grpc_credentials_metadata_request_create(creds, cb, user_data));
+    grpc_credentials_metadata_request *cb_arg =
+        grpc_credentials_metadata_request_create(creds, cb, user_data);
+    grpc_iomgr_closure_init(cb_arg->on_simulated_token_fetch_done_closure,
+                            on_simulated_token_fetch_done, cb_arg);
+    grpc_iomgr_add_callback(cb_arg->on_simulated_token_fetch_done_closure);
   } else {
     cb(user_data, c->access_token_md->entries, 1, GRPC_CREDENTIALS_OK);
   }

src/core/surface/call.c

@@ -227,6 +227,7 @@ struct grpc_call {
 
   gpr_slice_buffer incoming_message;
   gpr_uint32 incoming_message_length;
+  grpc_iomgr_closure destroy_closure;
 };
 
 #define CALL_STACK_FROM_CALL(call) ((grpc_call_stack *)((call) + 1))
@@ -370,7 +371,9 @@ void grpc_call_internal_unref(grpc_call *c, int allow_immediate_deletion) {
     if (allow_immediate_deletion) {
       destroy_call(c, 1);
     } else {
-      grpc_iomgr_add_callback(destroy_call, c);
+      c->destroy_closure.cb = destroy_call;
+      c->destroy_closure.cb_arg = c;
+      grpc_iomgr_add_callback(&c->destroy_closure);
     }
   }
 }

src/core/surface/channel.c

@@ -61,6 +61,7 @@ struct grpc_channel {
 
   gpr_mu registered_call_mu;
   registered_call *registered_calls;
+  grpc_iomgr_closure destroy_closure;
 };
 
 #define CHANNEL_STACK_FROM_CHANNEL(c) ((grpc_channel_stack *)((c) + 1))
@@ -193,7 +194,9 @@ static void destroy_channel(void *p, int ok) {
 
 void grpc_channel_internal_unref(grpc_channel *channel) {
   if (gpr_unref(&channel->refs)) {
-    grpc_iomgr_add_callback(destroy_channel, channel);
+    channel->destroy_closure.cb = destroy_channel;
+    channel->destroy_closure.cb_arg = channel;
+    grpc_iomgr_add_callback(&channel->destroy_closure);
   }
 }
 

src/core/surface/server.c

@@ -122,6 +122,8 @@ struct channel_data {
   channel_registered_method *registered_methods;
   gpr_uint32 registered_method_slots;
   gpr_uint32 registered_method_max_probes;
+  grpc_iomgr_closure finish_shutdown_channel_closure;
+  grpc_iomgr_closure finish_destroy_channel_closure;
 };
 
 struct grpc_server {
@@ -178,6 +180,8 @@ struct call_data {
   void (*on_done_recv)(void *user_data, int success);
   void *recv_user_data;
 
+  grpc_iomgr_closure kill_zombie_closure;
+
   call_data **root[CALL_LIST_COUNT];
   call_link links[CALL_LIST_COUNT];
 };
@@ -304,7 +308,9 @@ static void destroy_channel(channel_data *chand) {
   GPR_ASSERT(chand->server != NULL);
   orphan_channel(chand);
   server_ref(chand->server);
-  grpc_iomgr_add_callback(finish_destroy_channel, chand);
+  chand->finish_destroy_channel_closure.cb = finish_destroy_channel;
+  chand->finish_destroy_channel_closure.cb_arg = chand;
+  grpc_iomgr_add_callback(&chand->finish_destroy_channel_closure);
 }
 
 static void finish_start_new_rpc_and_unlock(grpc_server *server,
@@ -416,7 +422,8 @@ static void server_on_recv(void *ptr, int success) {
       gpr_mu_lock(&chand->server->mu);
       if (calld->state == NOT_STARTED) {
         calld->state = ZOMBIED;
-        grpc_iomgr_add_callback(kill_zombie, elem);
+        grpc_iomgr_closure_init(&calld->kill_zombie_closure, kill_zombie, elem);
+        grpc_iomgr_add_callback(&calld->kill_zombie_closure);
       }
       gpr_mu_unlock(&chand->server->mu);
       break;
@@ -424,11 +431,14 @@ static void server_on_recv(void *ptr, int success) {
       gpr_mu_lock(&chand->server->mu);
       if (calld->state == NOT_STARTED) {
         calld->state = ZOMBIED;
-        grpc_iomgr_add_callback(kill_zombie, elem);
+        grpc_iomgr_closure_init(&calld->kill_zombie_closure, kill_zombie, elem);
+        grpc_iomgr_add_callback(&calld->kill_zombie_closure);
       } else if (calld->state == PENDING) {
         call_list_remove(calld, PENDING_START);
         calld->state = ZOMBIED;
-        grpc_iomgr_add_callback(kill_zombie, elem);
+        grpc_iomgr_closure_init(&calld->kill_zombie_closure, kill_zombie, elem);
+        grpc_iomgr_add_callback(&calld->kill_zombie_closure);
+
       }
       gpr_mu_unlock(&chand->server->mu);
       break;
@@ -502,7 +512,9 @@ static void finish_shutdown_channel(void *cd, int success) {
 
 static void shutdown_channel(channel_data *chand) {
   grpc_channel_internal_ref(chand->channel);
-  grpc_iomgr_add_callback(finish_shutdown_channel, chand);
+  chand->finish_shutdown_channel_closure.cb = finish_shutdown_channel;
+  chand->finish_shutdown_channel_closure.cb_arg = chand;
+  grpc_iomgr_add_callback(&chand->finish_shutdown_channel_closure);
 }
 
 static void init_call_elem(grpc_call_element *elem,
@@ -949,11 +961,15 @@ void grpc_server_destroy(grpc_server *server) {
 
   while ((calld = call_list_remove_head(&server->lists[PENDING_START],
                                         PENDING_START)) != NULL) {
+    /* TODO(dgq): If we knew the size of the call list (or an upper bound), we
+     * could allocate all the memory for the closures in advance in a single
+     * chunk */
     gpr_log(GPR_DEBUG, "server destroys call %p", calld->call);
     calld->state = ZOMBIED;
-    grpc_iomgr_add_callback(
-        kill_zombie,
+    grpc_iomgr_closure_init(
+        &calld->kill_zombie_closure, kill_zombie,
         grpc_call_stack_element(grpc_call_get_call_stack(calld->call), 0));
+    grpc_iomgr_add_callback(&calld->kill_zombie_closure);
   }
 
   for (c = server->root_channel_data.next; c != &server->root_channel_data;

test/core/iomgr/alarm_test.c

@@ -55,6 +55,7 @@ void no_op_cb(void *arg, int success) {}
 typedef struct {
   gpr_cv cv;
   gpr_mu mu;
+  grpc_iomgr_closure *followup_closure;
   int counter;
   int done_success_ctr;
   int done_cancel_ctr;
@@ -81,7 +82,8 @@ static void alarm_cb(void *arg /* alarm_arg */, int success) {
   a->success = success;
   gpr_cv_signal(&a->cv);
   gpr_mu_unlock(&a->mu);
-  grpc_iomgr_add_callback(followup_cb, &a->fcb_arg);
+  grpc_iomgr_closure_init(a->followup_closure, followup_cb, &a->fcb_arg);
+  grpc_iomgr_add_callback(a->followup_closure);
 }
 
 /* Test grpc_alarm add and cancel. */
@@ -107,6 +109,7 @@ static void test_grpc_alarm(void) {
   arg.done = 0;
   gpr_mu_init(&arg.mu);
   gpr_cv_init(&arg.cv);
+  arg.followup_closure = gpr_malloc(sizeof(grpc_iomgr_closure));
   gpr_event_init(&arg.fcb_arg);
 
   grpc_alarm_init(&alarm, GRPC_TIMEOUT_MILLIS_TO_DEADLINE(100), alarm_cb, &arg,
@@ -148,6 +151,7 @@ static void test_grpc_alarm(void) {
   }
   gpr_cv_destroy(&arg.cv);
   gpr_mu_destroy(&arg.mu);
+  gpr_free(arg.followup_closure);
 
   arg2.counter = 0;
   arg2.success = SUCCESS_NOT_SET;
@@ -156,6 +160,8 @@ static void test_grpc_alarm(void) {
   arg2.done = 0;
   gpr_mu_init(&arg2.mu);
   gpr_cv_init(&arg2.cv);
+  arg2.followup_closure = gpr_malloc(sizeof(grpc_iomgr_closure));
+
   gpr_event_init(&arg2.fcb_arg);
 
   grpc_alarm_init(&alarm_to_cancel, GRPC_TIMEOUT_MILLIS_TO_DEADLINE(100),
@@ -206,6 +212,7 @@ static void test_grpc_alarm(void) {
   }
   gpr_cv_destroy(&arg2.cv);
   gpr_mu_destroy(&arg2.mu);
+  gpr_free(arg2.followup_closure);
 
   grpc_iomgr_shutdown();
 }