From fa576b00d7112717062b58c38000c512e9566919 Mon Sep 17 00:00:00 2001
From: Benjamin Summers <benjamin@tlon.io>
Date: Mon, 12 Nov 2018 12:20:32 -0800
Subject: [PATCH] Implemented u3t_boff for Linux.

---
 noun/trace.c | 88 +++++++++++++++++++++-------------------------------
 1 file changed, 35 insertions(+), 53 deletions(-)

diff --git a/noun/trace.c b/noun/trace.c
index a482b2e107..0fbe833243 100644
--- a/noun/trace.c
+++ b/noun/trace.c
@@ -388,58 +388,34 @@ u3t_boot(void)
 {
   if ( u3C.wag_w & u3o_debug_cpu ) { 
     _ct_lop_o = c3n;
-#if defined(U3_OS_osx)
-#if 1
+#if defined(U3_OS_osx) || defined(U3_OS_linux)
+    // Register _ct_sigaction to be called on `SIGPROF`.
     {
-      struct itimerval itm_v;
-      struct sigaction sig_s;
-      sigset_t set;
-
-      sig_s.__sigaction_u.__sa_handler = _ct_sigaction;
-      sig_s.sa_mask = 0;
-      sig_s.sa_flags = 0;
-      sigaction(SIGPROF, &sig_s, 0);
-
-      sigemptyset(&set);
-      sigaddset(&set, SIGPROF);
-      if ( 0 != pthread_sigmask(SIG_UNBLOCK, &set, NULL) ) {
-        perror("pthread_sigmask");
-      }
-
-      itm_v.it_interval.tv_sec = 0;
-      itm_v.it_interval.tv_usec = 10000;
-      // itm_v.it_interval.tv_usec = 100000;
-      itm_v.it_value = itm_v.it_interval;
-
-      setitimer(ITIMER_PROF, &itm_v, 0);
-    }
-#endif
-#elif defined(U3_OS_linux)
-    {
-      struct itimerval itm_v;
-      struct sigaction sig_s;
-      sigset_t set;
-
+      struct sigaction sig_s = {0};
       sig_s.sa_handler = _ct_sigaction;
       sigemptyset(&(sig_s.sa_mask));
-      sig_s.sa_flags = 0;
       sigaction(SIGPROF, &sig_s, 0);
+    }
 
+    // Unblock `SIGPROF` for this thread (we will block it again when `u3t_boff` is called).
+    {
+      sigset_t set;
       sigemptyset(&set);
       sigaddset(&set, SIGPROF);
       if ( 0 != pthread_sigmask(SIG_UNBLOCK, &set, NULL) ) {
         perror("pthread_sigmask");
       }
+    }
 
-      itm_v.it_interval.tv_sec = 0;
+    // Ask for SIGPROF to be sent every 10ms.
+    {
+      struct itimerval itm_v = {0};
       itm_v.it_interval.tv_usec = 10000;
-      // itm_v.it_interval.tv_usec = 100000;
       itm_v.it_value = itm_v.it_interval;
-
       setitimer(ITIMER_PROF, &itm_v, 0);
     }
 #elif defined(U3_OS_bsd)
-    // TODO: support profiling on bsd
+#   error "Profiling isn't yet supported on BSD"
 #else
 #   error "port: profiling"
 #endif
@@ -452,28 +428,34 @@ void
 u3t_boff(void)
 {
   if ( u3C.wag_w & u3o_debug_cpu ) {
-#if defined(U3_OS_osx)
-    struct sigaction sig_s;
-    struct itimerval itm_v;
-    sigset_t set;
-
-    sigemptyset(&set);
-    sigaddset(&set, SIGPROF);
-    if ( 0 != pthread_sigmask(SIG_BLOCK, &set, NULL) ) {
-      perror("pthread_sigmask");
+#if defined(U3_OS_osx) || defined(U3_OS_linux)
+    // Mask SIGPROF signals in this thread (and this is the only
+    // thread that unblocked them).
+    {
+      sigset_t set;
+      sigemptyset(&set);
+      sigaddset(&set, SIGPROF);
+      if ( 0 != pthread_sigmask(SIG_BLOCK, &set, NULL) ) {
+        perror("pthread_sigmask");
+      }
     }
 
-    itm_v.it_interval.tv_sec = 0;
-    itm_v.it_interval.tv_usec = 0;
-    itm_v.it_value = itm_v.it_interval;
+    // Disable the SIGPROF timer.
+    {
+      struct itimerval itm_v = {0};
+      setitimer(ITIMER_PROF, &itm_v, 0);
+    }
 
-    setitimer(ITIMER_PROF, &itm_v, 0);
-    sigaction(SIGPROF, &sig_s, 0);
+    // Ignore SIGPROF signals.
+    {
+      struct sigaction sig_s = {0};
+      sigemptyset(&(sig_s.sa_mask));
+      sig_s.sa_handler = SIG_IGN;
+      sigaction(SIGPROF, &sig_s, 0);
+    }
 
-#elif defined(U3_OS_linux)
-    // TODO: support profiling on linux
 #elif defined(U3_OS_bsd)
-    // TODO: support profiling on bsd
+#   error "Profiling isn't yet supported on BSD"
 #else
 #   error "port: profiling"
 #endif