picoev: fix for windows apps with veb in a thread, parallel to a webview, that opens a lot of file descriptors (#23492)

vlib/picoev/constants_default.c.v

@@ -0,0 +1,6 @@
+module picoev
+
+// max_fds is the maximum number of file descriptors that can be managed.
+// Many sizes depend on it, and some internal arrays are also iterated based on it,
+// so increasing it a lot can slow down looping :-| .
+pub const max_fds = 1024

vlib/picoev/constants_windows.c.v

@@ -0,0 +1,11 @@
+module picoev
+
+// max_fds is the maximum number of file descriptors that can be managed.
+// Many sizes depend on it, and some internal arrays are also iterated based on it,
+// so increasing it a lot can slow down looping :-| .
+// It is higher on windows, because if you start a veb/picoev webservice in a thread,
+// the returned file descriptors can be higher than 1024 in value, especially if you
+// also have a webview running in another thread, that also opens its own file descriptors.
+// Note: this works, because on windows we use select, and select on win32,
+// is not limited to polling on only 1024 fds.
+pub const max_fds = 4096

vlib/picoev/picoev.v

@@ -4,9 +4,6 @@ import net
 import picohttpparser
 import time
 
-// maximum number of file descriptors that can be managed
-pub const max_fds = 1024
-
 // maximum size of the event queue
 pub const max_queue = 4096
 
@@ -70,12 +67,12 @@ pub struct Picoev {
 	max_write    int = 8192
 mut:
 	loop             &LoopType = unsafe { nil }
-	file_descriptors [max_fds]&Target
+	file_descriptors [4096]&Target // TODO: use max_fds here, instead of the hardcoded size, when the compiler allows it
 	timeouts         map[int]i64
 	num_loops        int
 
 	buf &u8 = unsafe { nil }
-	idx [1024]int
+	idx [max_fds]int
 	out &u8 = unsafe { nil }
 
 	date string
@@ -192,6 +189,7 @@ fn accept_callback(listen_fd int, events int, cb_arg voidptr) {
 	}
 	if accepted_fd >= max_fds {
 		// should never happen
+		elog('Error during accept, accepted_fd >= max_fd')
 		close_socket(accepted_fd)
 		return
 	}