Add condition variable polling engine

11 files changed, 567 insertions, 5 deletions

diff --git a/src/core/lib/iomgr/ev_epoll_linux.c b/src/core/lib/iomgr/ev_epoll_linux.c
index ab77ebc78b..249bc98735 100644
--- a/src/core/lib/iomgr/ev_epoll_linux.c
+++ b/src/core/lib/iomgr/ev_epoll_linux.c
@@ -1892,6 +1892,10 @@ const grpc_event_engine_vtable *grpc_init_epoll_linux(void) {
     return NULL;
   }
 
+  if (!grpc_has_wakeup_fd) {
+    return NULL;
+  }
+
   if (!is_epoll_available()) {
     return NULL;
   }
diff --git a/src/core/lib/iomgr/ev_poll_cv_posix.c b/src/core/lib/iomgr/ev_poll_cv_posix.c
new file mode 100644
index 0000000000..dd1bbedcc1
--- /dev/null
+++ b/src/core/lib/iomgr/ev_poll_cv_posix.c
@@ -0,0 +1,297 @@
+/*
+ *
+ * Copyright 2016, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#include <grpc/support/port_platform.h>
+
+#ifdef GPR_POSIX_SOCKET
+
+#include "src/core/lib/iomgr/ev_poll_cv_posix.h"
+
+#include <errno.h>
+#include <string.h>
+
+#include <grpc/support/alloc.h>
+#include <grpc/support/log.h>
+#include <grpc/support/sync.h>
+#include <grpc/support/thd.h>
+#include <grpc/support/time.h>
+#include <grpc/support/useful.h>
+
+#include "src/core/lib/iomgr/ev_poll_posix.h"
+#include "src/core/lib/iomgr/wakeup_fd_posix.h"
+
+#define POLL_PERIOD_MS 1000
+#define DEFAULT_TABLE_SIZE 16
+
+typedef enum status_t { INPROGRESS, COMPLETED, CANCELLED } status_t;
+
+typedef struct poll_args {
+  gpr_refcount refcount;
+  gpr_cv* cv;
+  struct pollfd* fds;
+  nfds_t nfds;
+  int timeout;
+  int retval;
+  int err;
+  status_t status;
+} poll_args;
+
+cv_fd_table g_cvfds;
+
+static void decref_poll_args(poll_args* args) {
+  if (gpr_unref(&args->refcount)) {
+    gpr_free(args->fds);
+    gpr_cv_destroy(args->cv);
+    gpr_free(args->cv);
+    gpr_free(args);
+  }
+}
+
+// Poll in a background thread
+static void run_poll(void* arg) {
+  int timeout, retval;
+  poll_args* pargs = (poll_args*)arg;
+  while (pargs->status == INPROGRESS) {
+    if (pargs->timeout < 0) {
+      timeout = POLL_PERIOD_MS;
+    } else {
+      timeout = GPR_MIN(POLL_PERIOD_MS, pargs->timeout);
+      pargs->timeout -= timeout;
+    }
+    retval = g_cvfds.poll(pargs->fds, pargs->nfds, timeout);
+    if (retval != 0 || pargs->timeout == 0) {
+      pargs->retval = retval;
+      pargs->err = errno;
+      break;
+    }
+  }
+  gpr_mu_lock(&g_cvfds.mu);
+  if (pargs->status == INPROGRESS) {
+    // Signal main thread that the poll completed
+    pargs->status = COMPLETED;
+    gpr_cv_signal(pargs->cv);
+  }
+  decref_poll_args(pargs);
+  g_cvfds.pollcount--;
+  if (g_cvfds.shutdown && g_cvfds.pollcount == 0) {
+    gpr_cv_signal(&g_cvfds.shutdown_complete);
+  }
+  gpr_mu_unlock(&g_cvfds.mu);
+}
+
+// This function overrides poll() to handle condition variable wakeup fds
+static int cvfd_poll(struct pollfd* fds, nfds_t nfds, int timeout) {
+  unsigned int i;
+  int res, idx;
+  gpr_cv* pollcv;
+  cv_node *cvn, *prev;
+  nfds_t nsockfds = 0;
+  gpr_thd_id t_id;
+  gpr_thd_options opt;
+  poll_args* pargs = NULL;
+  gpr_mu_lock(&g_cvfds.mu);
+  pollcv = gpr_malloc(sizeof(gpr_cv));
+  gpr_cv_init(pollcv);
+  for (i = 0; i < nfds; i++) {
+    fds[i].revents = 0;
+    if (fds[i].fd < 0 && (fds[i].events & POLLIN)) {
+      idx = FD_TO_IDX(fds[i].fd);
+      cvn = gpr_malloc(sizeof(cv_node));
+      cvn->cv = pollcv;
+      cvn->next = g_cvfds.cvfds[idx].cvs;
+      g_cvfds.cvfds[idx].cvs = cvn;
+      // We should return immediately if there are pending events,
+      // but we still need to call poll() to check for socket events
+      if (g_cvfds.cvfds[idx].is_set) {
+        timeout = 0;
+      }
+    } else if (fds[i].fd >= 0) {
+      nsockfds++;
+    }
+  }
+
+  if (nsockfds > 0) {
+    pargs = gpr_malloc(sizeof(struct poll_args));
+    // Both the main thread and calling thread get a reference
+    gpr_ref_init(&pargs->refcount, 2);
+    pargs->cv = pollcv;
+    pargs->fds = gpr_malloc(sizeof(struct pollfd) * nsockfds);
+    pargs->nfds = nsockfds;
+    pargs->timeout = timeout;
+    pargs->retval = 0;
+    pargs->err = 0;
+    pargs->status = INPROGRESS;
+    idx = 0;
+    for (i = 0; i < nfds; i++) {
+      if (fds[i].fd >= 0) {
+        pargs->fds[idx].fd = fds[i].fd;
+        pargs->fds[idx].events = fds[i].events;
+        pargs->fds[idx].revents = 0;
+        idx++;
+      }
+    }
+    g_cvfds.pollcount++;
+    opt = gpr_thd_options_default();
+    gpr_thd_options_set_detached(&opt);
+    gpr_thd_new(&t_id, &run_poll, pargs, &opt);
+    // We want the poll() thread to trigger the deadline, so wait forever here
+    gpr_cv_wait(pollcv, &g_cvfds.mu, gpr_inf_future(GPR_CLOCK_MONOTONIC));
+    if (pargs->status == COMPLETED) {
+      res = pargs->retval;
+      errno = pargs->err;
+    } else {
+      res = 0;
+      errno = 0;
+      pargs->status = CANCELLED;
+    }
+  } else {
+    gpr_timespec deadline = gpr_now(GPR_CLOCK_REALTIME);
+    deadline =
+        gpr_time_add(deadline, gpr_time_from_millis(timeout, GPR_TIMESPAN));
+    gpr_cv_wait(pollcv, &g_cvfds.mu, deadline);
+    res = 0;
+  }
+
+  idx = 0;
+  for (i = 0; i < nfds; i++) {
+    if (fds[i].fd < 0 && (fds[i].events & POLLIN)) {
+      cvn = g_cvfds.cvfds[FD_TO_IDX(fds[i].fd)].cvs;
+      prev = NULL;
+      while (cvn->cv != pollcv) {
+        prev = cvn;
+        cvn = cvn->next;
+        GPR_ASSERT(cvn);
+      }
+      if (!prev) {
+        g_cvfds.cvfds[FD_TO_IDX(fds[i].fd)].cvs = cvn->next;
+      } else {
+        prev->next = cvn->next;
+      }
+      gpr_free(cvn);
+
+      if (g_cvfds.cvfds[FD_TO_IDX(fds[i].fd)].is_set) {
+        fds[i].revents = POLLIN;
+        if (res >= 0) res++;
+      }
+    } else if (fds[i].fd >= 0 && pargs->status == COMPLETED) {
+      fds[i].revents = pargs->fds[idx].revents;
+      idx++;
+    }
+  }
+
+  if (pargs) {
+    decref_poll_args(pargs);
+  } else {
+    gpr_cv_destroy(pollcv);
+    gpr_free(pollcv);
+  }
+  gpr_mu_unlock(&g_cvfds.mu);
+
+  return res;
+}
+
+static void grpc_global_cv_fd_table_init() {
+  gpr_mu_init(&g_cvfds.mu);
+  gpr_mu_lock(&g_cvfds.mu);
+  gpr_cv_init(&g_cvfds.shutdown_complete);
+  g_cvfds.shutdown = 0;
+  g_cvfds.pollcount = 0;
+  g_cvfds.size = DEFAULT_TABLE_SIZE;
+  g_cvfds.cvfds = gpr_malloc(sizeof(fd_node) * DEFAULT_TABLE_SIZE);
+  g_cvfds.free_fds = NULL;
+  for (int i = 0; i < DEFAULT_TABLE_SIZE; i++) {
+    g_cvfds.cvfds[i].is_set = 0;
+    g_cvfds.cvfds[i].cvs = NULL;
+    g_cvfds.cvfds[i].next_free = g_cvfds.free_fds;
+    g_cvfds.free_fds = &g_cvfds.cvfds[i];
+  }
+  // Override the poll function with one that supports cvfds
+  g_cvfds.poll = grpc_poll_function;
+  grpc_poll_function = &cvfd_poll;
+  gpr_mu_unlock(&g_cvfds.mu);
+}
+
+static void grpc_global_cv_fd_table_shutdown() {
+  gpr_mu_lock(&g_cvfds.mu);
+  g_cvfds.shutdown = 1;
+  // Attempt to wait for all abandoned poll() threads to terminate
+  // Not doing so will result in reported memory leaks
+  if (g_cvfds.pollcount > 0) {
+    int res = gpr_cv_wait(&g_cvfds.shutdown_complete, &g_cvfds.mu,
+                          gpr_time_add(gpr_now(GPR_CLOCK_REALTIME),
+                                       gpr_time_from_seconds(3, GPR_TIMESPAN)));
+    GPR_ASSERT(res == 0);
+  }
+  gpr_cv_destroy(&g_cvfds.shutdown_complete);
+  grpc_poll_function = g_cvfds.poll;
+  gpr_free(g_cvfds.cvfds);
+  gpr_mu_unlock(&g_cvfds.mu);
+  gpr_mu_destroy(&g_cvfds.mu);
+}
+
+/*******************************************************************************
+ * event engine binding
+ */
+
+static const grpc_event_engine_vtable* ev_poll_vtable;
+static grpc_event_engine_vtable vtable;
+
+static void shutdown_engine(void) {
+  ev_poll_vtable->shutdown_engine();
+  grpc_global_cv_fd_table_shutdown();
+}
+
+const grpc_event_engine_vtable* grpc_init_poll_cv_posix(void) {
+  int has_wakeup_fd = grpc_has_wakeup_fd;
+  int allow_specialized_wakeup_fd = grpc_allow_specialized_wakeup_fd;
+  int allow_pipe_wakeup_fd = grpc_allow_pipe_wakeup_fd;
+  grpc_global_cv_fd_table_init();
+  grpc_allow_specialized_wakeup_fd = 0;
+  grpc_allow_pipe_wakeup_fd = 0;
+  grpc_wakeup_fd_global_init();
+  grpc_has_wakeup_fd = 1;
+  ev_poll_vtable = grpc_init_poll_posix();
+  if (!ev_poll_vtable) {
+    grpc_global_cv_fd_table_shutdown();
+    grpc_has_wakeup_fd = has_wakeup_fd;
+    grpc_allow_specialized_wakeup_fd = allow_specialized_wakeup_fd;
+    grpc_allow_pipe_wakeup_fd = allow_pipe_wakeup_fd;
+    grpc_global_cv_fd_table_init();
+    return NULL;
+  }
+  vtable = *ev_poll_vtable;
+  vtable.shutdown_engine = shutdown_engine;
+  return &vtable;
+}
+
+#endif /* GPR_POSIX_SOCKET */
diff --git a/src/core/lib/iomgr/ev_poll_cv_posix.h b/src/core/lib/iomgr/ev_poll_cv_posix.h
new file mode 100644
index 0000000000..885711d1c5
--- /dev/null
+++ b/src/core/lib/iomgr/ev_poll_cv_posix.h
@@ -0,0 +1,68 @@
+/*
+ *
+ * Copyright 2016, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#ifndef GRPC_CORE_LIB_IOMGR_EV_POLL_CV_POSIX_H
+#define GRPC_CORE_LIB_IOMGR_EV_POLL_CV_POSIX_H
+
+#include <grpc/support/sync.h>
+
+#include "src/core/lib/iomgr/ev_posix.h"
+
+#define FD_TO_IDX(fd) (-(fd)-1)
+#define IDX_TO_FD(idx) (-(idx)-1)
+
+typedef struct cv_node {
+  gpr_cv* cv;
+  struct cv_node* next;
+} cv_node;
+
+typedef struct fd_node {
+  int is_set;
+  cv_node* cvs;
+  struct fd_node* next_free;
+} fd_node;
+
+typedef struct cv_fd_table {
+  gpr_mu mu;
+  int pollcount;
+  int shutdown;
+  gpr_cv shutdown_complete;
+  fd_node* cvfds;
+  fd_node* free_fds;
+  unsigned int size;
+  grpc_poll_function_type poll;
+} cv_fd_table;
+
+const grpc_event_engine_vtable* grpc_init_poll_cv_posix(void);
+
+#endif /* GRPC_CORE_LIB_IOMGR_EV_POLL_CV_POSIX_H */
diff --git a/src/core/lib/iomgr/ev_poll_posix.c b/src/core/lib/iomgr/ev_poll_posix.c
index 16a5e3083e..97e71d968e 100644
--- a/src/core/lib/iomgr/ev_poll_posix.c
+++ b/src/core/lib/iomgr/ev_poll_posix.c
@@ -1277,6 +1277,9 @@ static const grpc_event_engine_vtable vtable = {
 };
 
 const grpc_event_engine_vtable *grpc_init_poll_posix(void) {
+  if (!grpc_has_wakeup_fd) {
+    return NULL;
+  }
   if (!GRPC_LOG_IF_ERROR("pollset_global_init", pollset_global_init())) {
     return NULL;
   }
diff --git a/src/core/lib/iomgr/ev_posix.c b/src/core/lib/iomgr/ev_posix.c
index 6536672685..2fc8ccfa91 100644
--- a/src/core/lib/iomgr/ev_posix.c
+++ b/src/core/lib/iomgr/ev_posix.c
@@ -46,6 +46,7 @@
 
 #include "src/core/lib/iomgr/ev_epoll_linux.h"
 #include "src/core/lib/iomgr/ev_poll_and_epoll_posix.h"
+#include "src/core/lib/iomgr/ev_poll_cv_posix.h"
 #include "src/core/lib/iomgr/ev_poll_posix.h"
 #include "src/core/lib/support/env.h"
 
@@ -66,6 +67,7 @@ typedef struct {
 static const event_engine_factory g_factories[] = {
     {"epoll", grpc_init_epoll_linux},
     {"poll", grpc_init_poll_posix},
+    {"poll-cv", grpc_init_poll_cv_posix},
     {"legacy", grpc_init_poll_and_epoll_posix},
 };
 
diff --git a/src/core/lib/iomgr/wakeup_fd_cv.c b/src/core/lib/iomgr/wakeup_fd_cv.c
new file mode 100644
index 0000000000..651e2f663d
--- /dev/null
+++ b/src/core/lib/iomgr/wakeup_fd_cv.c
@@ -0,0 +1,118 @@
+/*
+ *
+ * Copyright 2016, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+#include <grpc/support/port_platform.h>
+
+#ifdef GPR_POSIX_WAKEUP_FD
+
+#include <errno.h>
+#include <string.h>
+
+#include <grpc/support/alloc.h>
+#include <grpc/support/log.h>
+#include <grpc/support/sync.h>
+#include <grpc/support/thd.h>
+#include <grpc/support/time.h>
+#include <grpc/support/useful.h>
+
+#include "src/core/lib/iomgr/ev_poll_cv_posix.h"
+
+#define MAX_TABLE_RESIZE 256
+
+extern cv_fd_table g_cvfds;
+
+static grpc_error* cv_fd_init(grpc_wakeup_fd* fd_info) {
+  unsigned int i, newsize;
+  int idx;
+  gpr_mu_lock(&g_cvfds.mu);
+  if (!g_cvfds.free_fds) {
+    newsize = GPR_MIN(g_cvfds.size * 2, g_cvfds.size + MAX_TABLE_RESIZE);
+    g_cvfds.cvfds = gpr_realloc(g_cvfds.cvfds, sizeof(fd_node) * newsize);
+    for (i = g_cvfds.size; i < newsize; i++) {
+      g_cvfds.cvfds[i].is_set = 0;
+      g_cvfds.cvfds[i].cvs = NULL;
+      g_cvfds.cvfds[i].next_free = g_cvfds.free_fds;
+      g_cvfds.free_fds = &g_cvfds.cvfds[i];
+    }
+    g_cvfds.size = newsize;
+  }
+
+  idx = (int)(g_cvfds.free_fds - g_cvfds.cvfds);
+  g_cvfds.free_fds = g_cvfds.free_fds->next_free;
+  g_cvfds.cvfds[idx].cvs = NULL;
+  g_cvfds.cvfds[idx].is_set = 0;
+  fd_info->read_fd = IDX_TO_FD(idx);
+  fd_info->write_fd = -1;
+  gpr_mu_unlock(&g_cvfds.mu);
+  return GRPC_ERROR_NONE;
+}
+
+static grpc_error* cv_fd_wakeup(grpc_wakeup_fd* fd_info) {
+  cv_node* cvn;
+  gpr_mu_lock(&g_cvfds.mu);
+  g_cvfds.cvfds[FD_TO_IDX(fd_info->read_fd)].is_set = 1;
+  cvn = g_cvfds.cvfds[FD_TO_IDX(fd_info->read_fd)].cvs;
+  while (cvn) {
+    gpr_cv_signal(cvn->cv);
+    cvn = cvn->next;
+  }
+  gpr_mu_unlock(&g_cvfds.mu);
+  return GRPC_ERROR_NONE;
+}
+
+static grpc_error* cv_fd_consume(grpc_wakeup_fd* fd_info) {
+  gpr_mu_lock(&g_cvfds.mu);
+  g_cvfds.cvfds[FD_TO_IDX(fd_info->read_fd)].is_set = 0;
+  gpr_mu_unlock(&g_cvfds.mu);
+  return GRPC_ERROR_NONE;
+}
+
+static void cv_fd_destroy(grpc_wakeup_fd* fd_info) {
+  if (fd_info->read_fd == 0) {
+    return;
+  }
+  gpr_mu_lock(&g_cvfds.mu);
+  // Assert that there are no active pollers
+  GPR_ASSERT(!g_cvfds.cvfds[FD_TO_IDX(fd_info->read_fd)].cvs);
+  g_cvfds.cvfds[FD_TO_IDX(fd_info->read_fd)].next_free = g_cvfds.free_fds;
+  g_cvfds.free_fds = &g_cvfds.cvfds[FD_TO_IDX(fd_info->read_fd)];
+  gpr_mu_unlock(&g_cvfds.mu);
+}
+
+static int cv_check_availability(void) { return 1; }
+
+const grpc_wakeup_fd_vtable grpc_cv_wakeup_fd_vtable = {
+    cv_fd_init, cv_fd_consume, cv_fd_wakeup, cv_fd_destroy,
+    cv_check_availability};
+
+#endif /* GPR_POSIX_WAKUP_FD */
diff --git a/src/core/lib/iomgr/wakeup_fd_cv.h b/src/core/lib/iomgr/wakeup_fd_cv.h
new file mode 100644
index 0000000000..e57fc28363
--- /dev/null
+++ b/src/core/lib/iomgr/wakeup_fd_cv.h
@@ -0,0 +1,55 @@
+/*
+ *
+ * Copyright 2016, Google Inc.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *     * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *     * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *     * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ *
+ */
+
+/*
+ * wakeup_fd_cv uses condition variables to implement wakeup fds.
+ *
+ * It is intended for use only in cases when eventfd() and pipe() are not
+ * available.  It can only be used with the "poll" engine.
+ *
+ * Implementation:
+ * A global table of cv wakeup fds is mantained.  A cv wakeup fd is a negative
+ * file descriptor.  poll() is then run in a background thread with only the
+ * real socket fds while we wait on a condition variable trigged by either the
+ * poll() completion or a wakeup_fd() call.
+ *
+ */
+
+#ifndef GRPC_CORE_LIB_IOMGR_WAKEUP_FD_CV_H
+#define GRPC_CORE_LIB_IOMGR_WAKEUP_FD_CV_H
+
+#include "src/core/lib/iomgr/wakeup_fd_posix.h"
+
+extern grpc_wakeup_fd_vtable grpc_cv_wakeup_fd_vtable;
+
+#endif /* GRPC_CORE_LIB_IOMGR_WAKEUP_FD_CV_H */
diff --git a/src/core/lib/iomgr/wakeup_fd_pipe.c b/src/core/lib/iomgr/wakeup_fd_pipe.c
index 4e5dbdcb73..d0ea216aa0 100644
--- a/src/core/lib/iomgr/wakeup_fd_pipe.c
+++ b/src/core/lib/iomgr/wakeup_fd_pipe.c
@@ -47,11 +47,10 @@
 
 static grpc_error* pipe_init(grpc_wakeup_fd* fd_info) {
   int pipefd[2];
-  /* TODO(klempner): Make this nonfatal */
   int r = pipe(pipefd);
   if (0 != r) {
     gpr_log(GPR_ERROR, "pipe creation failed (%d): %s", errno, strerror(errno));
-    abort();
+    return GRPC_OS_ERROR(errno, "pipe");
   }
   grpc_error* err;
   err = grpc_set_socket_nonblocking(pipefd[0], 1);
@@ -95,8 +94,13 @@ static void pipe_destroy(grpc_wakeup_fd* fd_info) {
 }
 
 static int pipe_check_availability(void) {
-  /* Assume that pipes are always available. */
-  return 1;
+  grpc_wakeup_fd fd;
+  if (pipe_init(&fd) == GRPC_ERROR_NONE) {
+    pipe_destroy(&fd);
+    return 1;
+  } else {
+    return 0;
+  }
 }
 
 const grpc_wakeup_fd_vtable grpc_pipe_wakeup_fd_vtable = {
diff --git a/src/core/lib/iomgr/wakeup_fd_posix.c b/src/core/lib/iomgr/wakeup_fd_posix.c
index 046208abc8..041c221de3 100644
--- a/src/core/lib/iomgr/wakeup_fd_posix.c
+++ b/src/core/lib/iomgr/wakeup_fd_posix.c
@@ -36,18 +36,25 @@
 #ifdef GPR_POSIX_WAKEUP_FD
 
 #include <stddef.h>
+#include "src/core/lib/iomgr/wakeup_fd_cv.h"
 #include "src/core/lib/iomgr/wakeup_fd_pipe.h"
 #include "src/core/lib/iomgr/wakeup_fd_posix.h"
 
 static const grpc_wakeup_fd_vtable *wakeup_fd_vtable = NULL;
 int grpc_allow_specialized_wakeup_fd = 1;
+int grpc_allow_pipe_wakeup_fd = 1;
+int grpc_has_wakeup_fd = 1;
 
 void grpc_wakeup_fd_global_init(void) {
   if (grpc_allow_specialized_wakeup_fd &&
       grpc_specialized_wakeup_fd_vtable.check_availability()) {
     wakeup_fd_vtable = &grpc_specialized_wakeup_fd_vtable;
-  } else {
+  } else if (grpc_allow_pipe_wakeup_fd &&
+             grpc_pipe_wakeup_fd_vtable.check_availability()) {
     wakeup_fd_vtable = &grpc_pipe_wakeup_fd_vtable;
+  } else {
+    grpc_has_wakeup_fd = 0;
+    wakeup_fd_vtable = &grpc_cv_wakeup_fd_vtable;
   }
 }
 
diff --git a/src/core/lib/iomgr/wakeup_fd_posix.h b/src/core/lib/iomgr/wakeup_fd_posix.h
index e269f242d8..bd0fb46da1 100644
--- a/src/core/lib/iomgr/wakeup_fd_posix.h
+++ b/src/core/lib/iomgr/wakeup_fd_posix.h
@@ -88,6 +88,8 @@ struct grpc_wakeup_fd {
 };
 
 extern int grpc_allow_specialized_wakeup_fd;
+extern int grpc_allow_pipe_wakeup_fd;
+extern int grpc_has_wakeup_fd;
 
 #define GRPC_WAKEUP_FD_GET_READ_FD(fd_info) ((fd_info)->read_fd)
 
diff --git a/src/python/grpcio/grpc_core_dependencies.py b/src/python/grpcio/grpc_core_dependencies.py
index 2bebf48c70..62d9729e13 100644
--- a/src/python/grpcio/grpc_core_dependencies.py
+++ b/src/python/grpcio/grpc_core_dependencies.py
@@ -102,6 +102,7 @@ CORE_SOURCE_FILES = [
   'src/core/lib/iomgr/error.c',
   'src/core/lib/iomgr/ev_epoll_linux.c',
   'src/core/lib/iomgr/ev_poll_and_epoll_posix.c',
+  'src/core/lib/iomgr/ev_poll_cv_posix.c',
   'src/core/lib/iomgr/ev_poll_posix.c',
   'src/core/lib/iomgr/ev_posix.c',
   'src/core/lib/iomgr/exec_ctx.c',
@@ -134,6 +135,7 @@ CORE_SOURCE_FILES = [
   'src/core/lib/iomgr/udp_server.c',
   'src/core/lib/iomgr/unix_sockets_posix.c',
   'src/core/lib/iomgr/unix_sockets_posix_noop.c',
+  'src/core/lib/iomgr/wakeup_fd_cv.c',
   'src/core/lib/iomgr/wakeup_fd_eventfd.c',
   'src/core/lib/iomgr/wakeup_fd_nospecial.c',
   'src/core/lib/iomgr/wakeup_fd_pipe.c',