twice termination delay only after SIGALRM, otherwise many separate SIGCHLD
and SIGIO signals quickly increase delay to the level when SIGKILL is sent

src/os/unix/ngx_process.c

diff --git a/src/os/unix/ngx_process.c b/src/os/unix/ngx_process.c
index f163651..48ba9d4 100644
--- a/src/os/unix/ngx_process.c
+++ b/src/os/unix/ngx_process.c
@@ -373,6 +373,7 @@
             break;
 
         case SIGALRM:
+            ngx_sigalrm = 1;
             break;
 
         case SIGIO:

src/os/unix/ngx_process_cycle.c

diff --git a/src/os/unix/ngx_process_cycle.c b/src/os/unix/ngx_process_cycle.c
index 9cf594d..21521ec 100644
--- a/src/os/unix/ngx_process_cycle.c
+++ b/src/os/unix/ngx_process_cycle.c
@@ -37,6 +37,7 @@
 
 sig_atomic_t  ngx_reap;
 sig_atomic_t  ngx_sigio;
+sig_atomic_t  ngx_sigalrm;
 sig_atomic_t  ngx_terminate;
 sig_atomic_t  ngx_quit;
 sig_atomic_t  ngx_debug_quit;
@@ -142,7 +143,10 @@
 
     for ( ;; ) {
         if (delay) {
-            delay *= 2;
+            if (ngx_sigalrm) {
+                delay *= 2;
+                ngx_sigalrm = 0;
+            }
 
             ngx_log_debug1(NGX_LOG_DEBUG_EVENT, cycle->log, 0,
                            "termination cycle: %d", delay);

src/os/unix/ngx_process_cycle.h

diff --git a/src/os/unix/ngx_process_cycle.h b/src/os/unix/ngx_process_cycle.h
index 8ef0c31..f46ad46 100644
--- a/src/os/unix/ngx_process_cycle.h
+++ b/src/os/unix/ngx_process_cycle.h
@@ -46,6 +46,7 @@
 
 extern sig_atomic_t    ngx_reap;
 extern sig_atomic_t    ngx_sigio;
+extern sig_atomic_t    ngx_sigalrm;
 extern sig_atomic_t    ngx_quit;
 extern sig_atomic_t    ngx_debug_quit;
 extern sig_atomic_t    ngx_terminate;