stubs: rework emulation of asynchronous resolver to use pipes

With a larger number of configured servers, the handler of the emulated
resolver repeatedly scheduled timeout of zero, which triggered the
infinite loop detection in the scheduler and caused abort. This bug was
introduced in commit 967e358dbc93aa7a99c3c0ee2a634f1fedecba74.

Rework the code to use pipes instead of timeouts to avoid this problem.

diff --git a/stubs.c b/stubs.c
index 9bc127cb8a3d5c727c3306afeb47c21675426505..f3ce4bb4ab4dd916cbd82caacbd8c1d5970e6a16 100644 (file)
--- a/stubs.c
+++ b/stubs.c
@@ -42,6 +42,7 @@
 #include "privops.h"
 #include "refclock.h"
 #include "sched.h"
+#include "util.h"
 
 #ifndef FEAT_ASYNCDNS
 
@@ -51,10 +52,11 @@ struct DNS_Async_Instance {
   const char *name;
   DNS_NameResolveHandler handler;
   void *arg;
+  int pipe[2];
 };
 
 static void
-resolve_name(void *anything)
+resolve_name(int fd, int event, void *anything)
 {
   struct DNS_Async_Instance *inst;
   IPAddr addrs[DNS_MAX_ADDRESSES];
@@ -62,6 +64,11 @@ resolve_name(void *anything)
   int i;
 
   inst = (struct DNS_Async_Instance *)anything;
+
+  SCH_RemoveFileHandler(inst->pipe[0]);
+  close(inst->pipe[0]);
+  close(inst->pipe[1]);
+
   status = PRV_Name2IPAddress(inst->name, addrs, DNS_MAX_ADDRESSES);
 
   for (i = 0; status == DNS_Success && i < DNS_MAX_ADDRESSES &&
@@ -83,7 +90,16 @@ DNS_Name2IPAddressAsync(const char *name, DNS_NameResolveHandler handler, void *
   inst->handler = handler;
   inst->arg = anything;
 
-  SCH_AddTimeoutByDelay(0.0, resolve_name, inst);
+  if (pipe(inst->pipe))
+    LOG_FATAL(LOGF_Nameserv, "pipe() failed");
+
+  UTI_FdSetCloexec(inst->pipe[0]);
+  UTI_FdSetCloexec(inst->pipe[1]);
+
+  SCH_AddFileHandler(inst->pipe[0], SCH_FILE_INPUT, resolve_name, inst);
+
+  if (write(inst->pipe[1], "", 1) < 0)
+    ;
 }
 
 #endif /* !FEAT_ASYNCDNS */