From 87fa5199ed4ac02b0da9cf92d1795ef360902f14 Mon Sep 17 00:00:00 2001
From: Eric Wong <e@80x24.org>
Date: Thu, 13 Mar 2014 03:06:54 +0000
Subject: [PATCH 2/2] speedup IO#close with many living threads

We only need to scan threads waiting on FDs on IO#close, not every
single thread.

A future improvement could be using a per-FD array of linked
lists for machines with many blocking threads.  This would cost
2 words of memory for every open FD, however.

Performance increases (over trunk) drastically with many threads not
waiting on IO:

	vm_thread_close 7.552
---
 thread.c  | 25 ++++++++++++-------------
 vm_core.h |  3 +++
 2 files changed, 15 insertions(+), 13 deletions(-)

diff --git a/thread.c b/thread.c
index 43a522a..0592afe 100644
--- a/thread.c
+++ b/thread.c
@@ -1341,6 +1341,7 @@ rb_thread_io_blocking_region(rb_blocking_function_t *func, void *data1, int fd)
     int state;
 
     th->waiting_fd = fd;
+    list_add(&th->vm->waitfd_threads, &th->waitfd_node);
 
     TH_PUSH_TAG(th);
     if ((state = EXEC_TAG()) == 0) {
@@ -1353,6 +1354,7 @@ rb_thread_io_blocking_region(rb_blocking_function_t *func, void *data1, int fd)
 
     /* clear waiting_fd anytime */
     th->waiting_fd = -1;
+    list_del(&th->waitfd_node);
 
     if (state) {
 	JUMP_TAG(state);
@@ -2059,22 +2061,19 @@ rb_threadptr_reset_raised(rb_thread_t *th)
     return 1;
 }
 
-static int
-thread_fd_close_i(rb_thread_t *th, void *fdp)
-{
-    int *fd = fdp;
-    if (th->waiting_fd == *fd) {
-	VALUE err = th->vm->special_exceptions[ruby_error_closed_stream];
-	rb_threadptr_pending_interrupt_enque(th, err);
-	rb_threadptr_interrupt(th);
-    }
-    return ST_CONTINUE;
-}
-
 void
 rb_thread_fd_close(int fd)
 {
-    rb_vm_living_threads_foreach(GET_THREAD()->vm, thread_fd_close_i, &fd);
+    rb_thread_t *th;
+    rb_vm_t *vm = GET_THREAD()->vm;
+
+    list_for_each(&vm->waitfd_threads, th, waitfd_node) {
+	if (th->waiting_fd == fd) {
+	    VALUE err = vm->special_exceptions[ruby_error_closed_stream];
+	    rb_threadptr_pending_interrupt_enque(th, err);
+	    rb_threadptr_interrupt(th);
+	}
+    }
 }
 
 /*
diff --git a/vm_core.h b/vm_core.h
index b71bb7a..262124b 100644
--- a/vm_core.h
+++ b/vm_core.h
@@ -333,6 +333,7 @@ typedef struct rb_vm_struct {
     struct rb_thread_struct *main_thread;
     struct rb_thread_struct *running_thread;
 
+    struct list_head waitfd_threads;
     struct list_head living_threads;
     size_t living_thread_num;
     VALUE thgroup_default;
@@ -519,6 +520,7 @@ typedef struct rb_thread_struct {
     int state;
 
     int waiting_fd;
+    struct list_node waitfd_node;
 
     /* for rb_iterate */
     const rb_block_t *passed_block;
@@ -860,6 +862,7 @@ void rb_thread_wakeup_timer_thread(void);
 static inline void
 rb_vm_living_threads_init(rb_vm_t *vm)
 {
+    list_head_init(&vm->waitfd_threads);
     list_head_init(&vm->living_threads);
     vm->living_thread_num = 0;
 }
-- 
1.9.rc2