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Fix FD_SETSIZE mismatch silently dropping watchers on Windows #103

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Merged
Watson1978 merged 1 commit into from
Jul 31, 2026
Merged

Fix FD_SETSIZE mismatch silently dropping watchers on Windows #103

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8 changes: 7 additions & 1 deletion ext/libev/ev.c
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Original file line number Diff line number Diff line change
Expand Up @@ -210,7 +210,13 @@
#else
# include <io.h>
# define WIN32_LEAN_AND_MEAN
# define FD_SETSIZE 1024
/* ruby.h above already pulled in winsock2.h, so fd_set may be dimensioned
* already. Defining FD_SETSIZE unconditionally here would only move the bound
* used by EV_WIN_FD_SET, not the array it indexes. Take whatever is in effect
* and only supply a default when nothing has been decided yet. */
# ifndef FD_SETSIZE
# define FD_SETSIZE 1024
# endif
# include <winsock2.h>
# include <windows.h>
# ifndef EV_SELECT_IS_WINSOCKET
Expand Down
10 changes: 10 additions & 0 deletions ext/libev/ev_select.c
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Original file line number Diff line number Diff line change
Expand Up @@ -107,6 +107,16 @@ if (__i == ((fd_set *)(set))->fd_count) {\
#define EV_WIN_FD_ZERO(set) (((fd_set *)(set))->fd_count=0)
#define EV_WIN_FD_ISSET(fd, set) __WSAFDIsSet((SOCKET)(fd), (fd_set *)(set))
#define EV_WIN_FD_COUNT(set) (((fd_set *)(set))->fd_count)

/*
fd_set is dimensioned by whatever FD_SETSIZE was in effect when winsock2.h was
first pulled in, but EV_WIN_FD_SET and select_modify bound-check against the
FD_SETSIZE visible here. The two are decided by separate paths, so if the bound
ever exceeds the declared array we would write past the end of the allocation in
select_init. Catch that at build time instead.
*/
typedef char coolio_fd_setsize_matches_fd_set[
(sizeof (((fd_set *)0)->fd_array) / sizeof (SOCKET) >= (size_t)FD_SETSIZE) ? 1 : -1];
/* ######################################## */
#else
#define EV_WIN_FD_CLR FD_CLR
Expand Down
34 changes: 25 additions & 9 deletions libev_win_select.diff
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Original file line number Diff line number Diff line change
@@ -1,20 +1,26 @@
diff --git a/ext/libev/ev.c b/ext/libev/ev.c
index dae87f1..d15f6bd 100644
index a59efb2..5c18fd6 100644
--- a/ext/libev/ev.c
+++ b/ext/libev/ev.c
@@ -207,6 +207,7 @@
@@ -210,6 +210,13 @@
#else
# include <io.h>
# define WIN32_LEAN_AND_MEAN
+# define FD_SETSIZE 1024
+/* ruby.h above already pulled in winsock2.h, so fd_set may be dimensioned
+ * already. Defining FD_SETSIZE unconditionally here would only move the bound
+ * used by EV_WIN_FD_SET, not the array it indexes. Take whatever is in effect
+ * and only supply a default when nothing has been decided yet. */
+# ifndef FD_SETSIZE
+# define FD_SETSIZE 1024
+# endif
# include <winsock2.h>
# include <windows.h>
# ifndef EV_SELECT_IS_WINSOCKET
diff --git a/ext/libev/ev_select.c b/ext/libev/ev_select.c
index f38d6ca..7050778 100644
index ed1fc7a..eccff2b 100644
--- a/ext/libev/ev_select.c
+++ b/ext/libev/ev_select.c
@@ -67,6 +67,54 @@
@@ -67,6 +67,64 @@

#include <string.h>

Expand Down Expand Up @@ -58,6 +64,16 @@ index f38d6ca..7050778 100644
+#define EV_WIN_FD_ZERO(set) (((fd_set *)(set))->fd_count=0)
+#define EV_WIN_FD_ISSET(fd, set) __WSAFDIsSet((SOCKET)(fd), (fd_set *)(set))
+#define EV_WIN_FD_COUNT(set) (((fd_set *)(set))->fd_count)
+
+/*
+fd_set is dimensioned by whatever FD_SETSIZE was in effect when winsock2.h was
+first pulled in, but EV_WIN_FD_SET and select_modify bound-check against the
+FD_SETSIZE visible here. The two are decided by separate paths, so if the bound
+ever exceeds the declared array we would write past the end of the allocation in
+select_init. Catch that at build time instead.
+*/
+typedef char coolio_fd_setsize_matches_fd_set[
+ (sizeof (((fd_set *)0)->fd_array) / sizeof (SOCKET) >= (size_t)FD_SETSIZE) ? 1 : -1];
+/* ######################################## */
+#else
+#define EV_WIN_FD_CLR FD_CLR
Expand All @@ -69,7 +85,7 @@ index f38d6ca..7050778 100644
static void
select_modify (EV_P_ int fd, int oev, int nev)
{
@@ -91,17 +139,17 @@ select_modify (EV_P_ int fd, int oev, int nev)
@@ -91,17 +149,17 @@ select_modify (EV_P_ int fd, int oev, int nev)
if ((oev ^ nev) & EV_READ)
#endif
if (nev & EV_READ)
Expand All @@ -91,7 +107,7 @@ index f38d6ca..7050778 100644

#else

@@ -197,8 +245,8 @@ select_poll (EV_P_ ev_tstamp timeout)
@@ -197,8 +255,8 @@ select_poll (EV_P_ ev_tstamp timeout)
{
if (timeout)
{
Expand All @@ -102,7 +118,7 @@ index f38d6ca..7050778 100644
}

return;
@@ -230,10 +278,10 @@ select_poll (EV_P_ ev_tstamp timeout)
@@ -230,10 +288,10 @@ select_poll (EV_P_ ev_tstamp timeout)
int handle = fd;
#endif

Expand All @@ -116,7 +132,7 @@ index f38d6ca..7050778 100644
#endif

if (expect_true (events))
@@ -279,9 +327,9 @@ select_init (EV_P_ int flags)
@@ -280,9 +338,9 @@ select_init (EV_P_ int flags)
backend_poll = select_poll;

#if EV_SELECT_USE_FD_SET
Expand Down