From 66197ca25d13f2725ba6d741868557fade1cc8c8 Mon Sep 17 00:00:00 2001
From: Craig Tiller <craig.tiller@gmail.com>
Date: Mon, 2 Nov 2015 08:04:10 -0800
Subject: [PATCH] Fix nap condition for pollset wakeup
If:
- one thread issues a kick forcing pollset re-evaluation
- concurrently with a second thread forcing a specific poller to be awoken
And:
- both threads kicks are processed as a single wakeup
Then:
- since we enqueue nothing to the exec_ctx in this situation, we responded to the wakeup by doing another poll until the timeout, ignoring urgent work up the stack
Fix this by flagging that a specific worker was designated to be awoken (since this is a good signal that we really really need to wake up), and use that to still re-evaluate the poll set, but with an immediate deadline so that we fall out of the poll loop as soon as possible.
---
src/core/iomgr/pollset_posix.c | 5 ++++-
src/core/iomgr/pollset_posix.h | 1 +
2 files changed, 5 insertions(+), 1 deletion(-)
diff --git a/src/core/iomgr/pollset_posix.c b/src/core/iomgr/pollset_posix.c
index bce1ce9714..6f478ccacb 100644
--- a/src/core/iomgr/pollset_posix.c
+++ b/src/core/iomgr/pollset_posix.c
@@ -121,12 +121,14 @@ void grpc_pollset_kick_ext(grpc_pollset *p,
if ((flags & GRPC_POLLSET_REEVALUATE_POLLING_ON_WAKEUP) != 0) {
specific_worker->reevaluate_polling_on_wakeup = 1;
}
+ specific_worker->kicked_specifically = 1;
grpc_wakeup_fd_wakeup(&specific_worker->wakeup_fd);
} else if ((flags & GRPC_POLLSET_CAN_KICK_SELF) != 0) {
GPR_TIMER_MARK("kick_yoself", 0);
if ((flags & GRPC_POLLSET_REEVALUATE_POLLING_ON_WAKEUP) != 0) {
specific_worker->reevaluate_polling_on_wakeup = 1;
}
+ specific_worker->kicked_specifically = 1;
grpc_wakeup_fd_wakeup(&specific_worker->wakeup_fd);
}
} else if (gpr_tls_get(&g_current_thread_poller) != (gpr_intptr)p) {
@@ -242,6 +244,7 @@ void grpc_pollset_work(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
/* this must happen before we (potentially) drop pollset->mu */
worker->next = worker->prev = NULL;
worker->reevaluate_polling_on_wakeup = 0;
+ worker->kicked_specifically = 0;
/* TODO(ctiller): pool these */
grpc_wakeup_fd_init(&worker->wakeup_fd);
/* If there's work waiting for the pollset to be idle, and the
@@ -308,7 +311,7 @@ void grpc_pollset_work(grpc_exec_ctx *exec_ctx, grpc_pollset *pollset,
if (worker->reevaluate_polling_on_wakeup) {
worker->reevaluate_polling_on_wakeup = 0;
pollset->kicked_without_pollers = 0;
- if (queued_work) {
+ if (queued_work || worker->kicked_specifically) {
/* If there's queued work on the list, then set the deadline to be
immediate so we get back out of the polling loop quickly */
deadline = gpr_inf_past(GPR_CLOCK_MONOTONIC);
diff --git a/src/core/iomgr/pollset_posix.h b/src/core/iomgr/pollset_posix.h
index 34f76db2af..95ebeab1c2 100644
--- a/src/core/iomgr/pollset_posix.h
+++ b/src/core/iomgr/pollset_posix.h
@@ -51,6 +51,7 @@ struct grpc_fd;
typedef struct grpc_pollset_worker {
grpc_wakeup_fd wakeup_fd;
int reevaluate_polling_on_wakeup;
+ int kicked_specifically;
struct grpc_pollset_worker *next;
struct grpc_pollset_worker *prev;
} grpc_pollset_worker;
--
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