From 938131f3315202a92005aa661ea01507405376a7 Mon Sep 17 00:00:00 2001
From: Guilherme Affonso <guilherme.c.affonso@gmail.com>
Date: Thu, 10 Nov 2022 18:20:04 +0900
Subject: [PATCH] Don't resume previously suspended threads on gc

---
 lisp/c/eus_proto.h     |   1 +
 lisp/c/eus_thr.h       |   1 +
 lisp/c/memory.c        |   4 +-
 lisp/c/mthread_posix.c | 115 +++++++++++++++++++----------------------
 4 files changed, 57 insertions(+), 64 deletions(-)

diff --git a/lisp/c/eus_proto.h b/lisp/c/eus_proto.h
index be8b5a8d9..183085e13 100644
--- a/lisp/c/eus_proto.h
+++ b/lisp/c/eus_proto.h
@@ -500,6 +500,7 @@ extern int thr_setprio(int /*tid*/, int /*prio*/);
 extern int thr_create(void */*base*/, size_t /*size*/, void (*/*func*/)(), void */*args*/, long /*flags*/, int */*tid*/);
 extern int thr_continue(int /*tid*/);
 extern int thr_suspend(int /*tid*/);
+extern int thr_unsuspend(int /*tid*/);
 extern int thr_kill(int /*tid*/, int /*sig*/);
 extern int thr_cancel(int /*tid*/);
 extern int thr_join(int /*tid*/, int */*depature*/, void **/*status*/);
diff --git a/lisp/c/eus_thr.h b/lisp/c/eus_thr.h
index a64ea0699..70e1e5157 100644
--- a/lisp/c/eus_thr.h
+++ b/lisp/c/eus_thr.h
@@ -113,6 +113,7 @@ extern int thr_create(void *, size_t, void (*)(), void *, long, int *);
 extern int thr_setprio(int, int);
 extern int thr_continue(int);
 extern int thr_suspend(int);
+extern int thr_unsuspend(int);
 extern int thr_kill(int, int);
 extern int thr_cancel(int);
 
diff --git a/lisp/c/memory.c b/lisp/c/memory.c
index e52dfd4ab..447e5cb35 100644
--- a/lisp/c/memory.c
+++ b/lisp/c/memory.c
@@ -762,7 +762,9 @@ void resume_all_threads()
   self=thr_self();
   for (i=0; i<MAXTHREAD; i++) 
     if (i!=self && euscontexts[i]) {
-      stat=thr_continue(i);
+      // Use thr_unsuspend to avoid resuming threads which were
+      // already suspended by the user before the gc
+      stat=thr_unsuspend(i);
       if (stat) fprintf(stderr, "gc cannot resume thread %d\n",i);  }
   }
 
diff --git a/lisp/c/mthread_posix.c b/lisp/c/mthread_posix.c
index d337a2d3e..509071316 100644
--- a/lisp/c/mthread_posix.c
+++ b/lisp/c/mthread_posix.c
@@ -122,8 +122,7 @@ pthread_mutex_t susp_mut = PTHREAD_MUTEX_INITIALIZER;
 volatile int susp_sentinel = 0;
 pthread_once_t susp_once = PTHREAD_ONCE_INIT;
 pthread_t susp_null_pthread = {0};
-pthread_t susp_array[MAXTHREAD]; 
-int susp_bottom = MAXTHREAD;
+int susp_count[MAXTHREAD];
 int susp_inited = 0;
 
 /*
@@ -134,14 +133,26 @@ void
 suspend_signal_handler (int sig)
 {
     sigset_t signal_set;
+    susp_count[thr_self()] += 1;
 
     /*
-     * Block all signals except SIGUSR2 while suspended.
+     * Skip if already suspended
+     */
+    if (susp_count[thr_self()]>1) {
+      susp_sentinel = 1;
+      return;
+    }
+
+    /*
+     * Block all signals except SIGUSR1 and SIGUSR2 while suspended.
      */
     sigfillset (&signal_set);
+    sigdelset (&signal_set, SIGUSR1);
     sigdelset (&signal_set, SIGUSR2);
     susp_sentinel = 1;
-    sigsuspend (&signal_set);
+    while(susp_count[thr_self()]>0) {
+      sigsuspend (&signal_set);
+    }
 
     /*
      * Once I'm here, I've been resumed, and the resume signal
@@ -158,6 +169,7 @@ suspend_signal_handler (int sig)
 void
 resume_signal_handler (int sig)
 {
+    susp_count[thr_self()] -= 1;
     return;
 }
 
@@ -168,15 +180,15 @@ resume_signal_handler (int sig)
 void
 suspend_init_routine (void)
 {
-    int status;
+    int i, status;
     struct sigaction sigusr1, sigusr2;
 
     /*
-     * Allocate the suspended threads array. This array is used
-     * to guarentee idempotency
+     * Initialize suspension counter
      */
-    //susp_bottom = 10;
-//    susp_array = (pthread_t*) calloc (susp_bottom, sizeof (pthread_t));
+    for (i=0; i<MAXTHREAD; i++) {
+      susp_count[i] = 0;
+    }
 
     /*
      * Install the signal handlers for suspend/resume.
@@ -210,11 +222,10 @@ suspend_init_routine (void)
  * call will cause it to resume execution.
  */
 int 
-//thd_suspend (pthread_t target_thread)
+//thr_suspend (pthread_t target_thread)
 pthread_suspend (pthread_t target_thread)
 {
     int status;
-    int i = 0;
 
     /*
      * The first call to thd_suspend will initialize the
@@ -231,38 +242,6 @@ pthread_suspend (pthread_t target_thread)
     if (status != 0)
         return status;
 
-    /*
-     * Threads that are suspended are added to the target_array;
-     * a request to suspend a thread already listed in the array
-     * is ignored. Sending a second SIGUSR1 would cause the
-     * thread to re-suspend itself as soon as it is resumed.
-     */
-    while (i < susp_bottom) 
-        if (susp_array[i++] == target_thread) {
-            status = pthread_mutex_unlock (&susp_mut);
-            return status;
-        }
-
-    /*
-     * Ok, we really need to suspend this thread. So, lets find
-     * the location in the array that we'll use. If we run off
-     * the end, realloc the array for more space.
-     */
-    i = 0;
-    while (susp_array[i] != 0)
-        i++;
-
-    if (i == susp_bottom) {
-//        susp_array = (pthread_t*) realloc (
-//            susp_array, (++susp_bottom * sizeof (pthread_t)));
-//        if (susp_array == NULL) {
-            pthread_mutex_unlock (&susp_mut);
-            return errno;
-//        }
-
-//        susp_array[susp_bottom] = susp_null_pthread;   /* Clear new entry */
-    }
-
     /*
      * Clear the sentinel and signal the thread to suspend.
      */
@@ -279,8 +258,6 @@ pthread_suspend (pthread_t target_thread)
     while (susp_sentinel == 0)
         sched_yield ();
     
-    susp_array[i] = target_thread;
-
     status = pthread_mutex_unlock (&susp_mut);
     return status;
 }
@@ -288,14 +265,15 @@ pthread_suspend (pthread_t target_thread)
 /*
  * Resume a suspended thread by sending it SIGUSR2 to break
  * it out of the sigsuspend() in which it's waiting. If the
- * target thread isn't suspended, return with success.
+ * thread has received other suspension requests while waiting,
+ * the thread will be re-suspended immediately after resuming.
+ * If the target thread isn't suspended, return with success.
  */
 int 
-//thd_continue (pthread_t target_thread)
-pthread_continue (pthread_t target_thread)
+pthread_unsuspend (pthread_t target_thread)
 {
     int status;
-    int i = 0;
+
     /* 
      * Serialize access to suspend, makes life easier
      */
@@ -312,19 +290,6 @@ pthread_continue (pthread_t target_thread)
         return status;
     }
 
-    /*
-     * Make sure the thread is in the suspend array. If not, it
-     * hasn't been suspended (or it has already been resumed) and
-     * we can just carry on.
-     */
-    while (susp_array[i] != target_thread && i < susp_bottom) 
-        i++;
-
-    if (i >= susp_bottom) {
-        pthread_mutex_unlock (&susp_mut);
-        return 0;
-    }
-
     /*
      * Signal the thread to continue, and remove the thread from
      * the suspended array.
@@ -335,10 +300,34 @@ pthread_continue (pthread_t target_thread)
         return status;
     }
 
-    susp_array[i] = 0;               /* Clear array element */
     status = pthread_mutex_unlock (&susp_mut);
     return status;
 }
+
+/*
+ * Ensures that a suspended thread is resumed, even if
+ * multiple suspension requests have been received.
+ */
+int
+//thr_continue (pthread_t target_thread)
+pthread_continue (pthread_t target_thread)
+{
+    int i;
+    for(i = 0; i < MAXTHREAD && !pthread_equal(thread_table[i].tid,target_thread); i++);
+    if (i == MAXTHREAD) return(-1);
+
+    susp_count[i] = 1;
+    return pthread_unsuspend(target_thread);
+}
+
+int thr_unsuspend( int tid ) {
+  return pthread_unsuspend( thread_table[tid].tid );
+}
+#else
+int thr_unsuspend( int tid ) {
+  // not supported, always continue
+  return pthread_continue ( thread_table[tid].tid );
+}
 #endif
 int thr_suspend( int tid ) { 
   return pthread_suspend ( thread_table[tid].tid );