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linux: work around epoll bug in kernels < 2.6.37

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Old 32 bits kernels (native and compat) have a bug where timeouts larger
than (LONG_MAX / CONFIG_HZ) milliseconds are treated as infinite.

Work around that by capping the timeout and polling again if necessary.

PR-URL: https://github.com/libuv/libuv/pull/354
Reviewed-By: Saúl Ibarra Corretgé <saghul@gmail.com>
This commit is contained in:
Ben Noordhuis 2015-05-15 17:14:23 +02:00
parent ccf90a1ea5
commit d1b5008e76
1 changed files with 25 additions and 4 deletions
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29
src/unix/linux-core.c
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@ -141,17 +141,26 @@ void uv__platform_invalidate_fd(uv_loop_t* loop, int fd) {
void uv__io_poll(uv_loop_t* loop, int timeout) {
/* A bug in kernels < 2.6.37 makes timeouts larger than ~30 minutes
* effectively infinite on 32 bits architectures. To avoid blocking
* indefinitely, we cap the timeout and poll again if necessary.
*
* Note that "30 minutes" is a simplification because it depends on
* the value of CONFIG_HZ. The magic constant assumes CONFIG_HZ=1200,
* that being the largest value I have seen in the wild (and only once.)
*/
static const int max_safe_timeout = 1789569;
static int no_epoll_pwait;
static int no_epoll_wait;
struct uv__epoll_event events[1024];
struct uv__epoll_event* pe;
struct uv__epoll_event e;
int real_timeout;
QUEUE* q;
uv__io_t* w;
sigset_t sigset;
uint64_t sigmask;
uint64_t base;
uint64_t diff;
int nevents;
int count;
int nfds;
@ -209,8 +218,15 @@ void uv__io_poll(uv_loop_t* loop, int timeout) {
assert(timeout >= -1);
base = loop->time;
count = 48; /* Benchmarks suggest this gives the best throughput. */
real_timeout = timeout;
for (;;) {
/* See the comment for max_safe_timeout for an explanation of why
* this is necessary. Executive summary: kernel bug workaround.
*/
if (sizeof(int32_t) == sizeof(long) && timeout >= max_safe_timeout)
timeout = max_safe_timeout;
if (sigmask != 0 && no_epoll_pwait != 0)
if (pthread_sigmask(SIG_BLOCK, &sigset, NULL))
abort();
@ -244,6 +260,11 @@ void uv__io_poll(uv_loop_t* loop, int timeout) {
if (nfds == 0) {
assert(timeout != -1);
timeout = real_timeout - timeout;
if (timeout > 0)
continue;
return;
}
@ -346,11 +367,11 @@ void uv__io_poll(uv_loop_t* loop, int timeout) {
update_timeout:
assert(timeout > 0);
diff = loop->time - base;
if (diff >= (uint64_t) timeout)
real_timeout -= (loop->time - base);
if (real_timeout <= 0)
return;
timeout -= diff;
timeout = real_timeout;
}
}