From 44c0fc2820bb13018b200d3ec990c30cdd2a08cd Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Wed, 25 Nov 2015 12:48:15 +0200
Subject: Add process::try_wait() for non-blocking wait

---
 butl/process     |  6 ++++++
 butl/process.cxx | 20 ++++++++++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/butl/process b/butl/process
index bbd0162..6077ad3 100644
--- a/butl/process
+++ b/butl/process
@@ -75,6 +75,12 @@ namespace butl
     bool
     wait ();
 
+    // Return true if the process has already terminated in which case
+    // the argument is set to the result of wait().
+    //
+    bool
+    try_wait (bool&);
+
     ~process () {if (id != 0) wait ();}
 
     // Move constructible-only type.
diff --git a/butl/process.cxx b/butl/process.cxx
index 66a831e..bd13392 100644
--- a/butl/process.cxx
+++ b/butl/process.cxx
@@ -121,6 +121,26 @@ namespace butl
     return WIFEXITED (status) && WEXITSTATUS (status) == 0;
   }
 
+  bool process::
+  try_wait (bool& s)
+  {
+    if (id != 0)
+    {
+      int r (waitpid (id, &status, WNOHANG));
+
+      if (r == 0) // Not exited yet.
+        return false;
+
+      id = 0; // We have tried.
+
+      if (r == -1)
+        throw process_error (errno, false);
+    }
+
+    s =  WIFEXITED (status) && WEXITSTATUS (status) == 0;
+    return true;
+  }
+
 #else // _WIN32
 
   static void
-- 
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