Fixing a bug and performance issue.

Problem: we are using sigsetjmp but with a jmp_buf structure;
it requires sigjmp_buf!

Performance issue: sigsetjmp is a dog which makes system calls.
Solution: let's roll our own cached version of sigprocmask which
only calls the real sigprocmask when the mask changes. Then
our extended_setjmp will just use regular setjmp, plus our own
custom signal saving and restoring based on the cached version.

* signal.c (sig_blocked_cache): New variable.
(set_sig_handler): Use our sig_mask instead of sigprocmask.
(mem_set_bits, mem_clr_bits): New static functions.
(sig_mask): New function.

* signal.h (extended_jmp_buf): New member, blocked.
(extended_setjmp): save blocked signals by peeking into
sig_blocked_cache, and restore using sig_mask.
(sig_blocked_cache, sig_mask): Declared.

1 files changed, 10 insertions, 3 deletions

diff --git a/signal.h b/signal.h
index e2b794c1..8882c259 100644
--- a/signal.h
+++ b/signal.h
@@ -60,17 +60,23 @@
 typedef struct {
   jmp_buf jb;
   sig_atomic_t se;
+  sigset_t blocked;
   int rv;
 } extended_jmp_buf;
 
 #define extended_setjmp(EJB)                    \
-  (sigsetjmp((EJB).jb, 1)                       \
-   ? (async_sig_enabled = (EJB).se, (EJB).rv)   \
-   : ((EJB).se = async_sig_enabled, 0))
+  (setjmp((EJB).jb)                             \
+   ? (async_sig_enabled = (EJB).se,             \
+      sig_mask(SIG_SETMASK, &(EJB).blocked, 0), \
+      (EJB).rv)                                 \
+   : ((EJB).se = async_sig_enabled,             \
+      (EJB).blocked = sig_blocked_cache, 0))
 
 #define extended_longjmp(EJB, ARG)              \
   ((EJB).rv = (ARG), longjmp((EJB).jb, 1))
 
+extern sigset_t sig_blocked_cache;
+
 #else
 
 #define sig_save_enable do {
@@ -98,3 +104,4 @@ void sig_init(void);
 val set_sig_handler(val signo, val lambda);
 val get_sig_handler(val signo);
 val sig_check(void);
+int sig_mask(int how, const sigset_t *set, sigset_t *oldset);