1 files changed, 78 insertions, 0 deletions
diff --git a/winsup/cygwin/local_includes/spinlock.h b/winsup/cygwin/local_includes/spinlock.h
new file mode 100644
index 000000000..d8ded1274
--- /dev/null
+++ b/winsup/cygwin/local_includes/spinlock.h
@@ -0,0 +1,78 @@
+/* spinlock.h: Header file for cygwin time-sensitive synchronization primitive.
+
+This file is part of Cygwin.
+
+This software is a copyrighted work licensed under the terms of the
+Cygwin license.  Please consult the file "CYGWIN_LICENSE" for
+details. */
+
+#ifndef _SPINLOCK_H
+#define _SPINLOCK_H
+
+#include "ntdll.h"
+
+#define SPINLOCK_WAIT (15000LL * 10000LL)
+
+class spinlock
+{
+  LONG *locker;
+  LONG val;
+  LONG setto;
+  void done (LONG what)
+  {
+    if (locker)
+      {
+	InterlockedExchange (locker, what);
+	locker = NULL;
+      }
+  }
+  long long time ()
+  {
+    LARGE_INTEGER t;
+    if (NtQuerySystemTime (&t) == STATUS_SUCCESS)
+      return t.QuadPart;
+    return 0LL;
+  }
+public:
+  spinlock (LONG& locktest, LONG wanted_val = 1, LONGLONG timeout = SPINLOCK_WAIT):
+    locker (&locktest), setto (wanted_val)
+  {
+    /* Quick test to see if we're already initialized */
+    if ((val = locktest) == wanted_val)
+      locker = NULL;
+    /* Slightly less quick test to see if we are the first cygwin process */
+    else if ((val = InterlockedExchange (locker, -1)) == 0)
+      /* We're armed and dangerous */;
+    else if (val == wanted_val)
+      done (val);	/* This was initialized while we weren't looking */
+    else
+      {
+	long long then = time ();
+	/* Loop waiting for some other process to set locktest to something
+	   other than -1, indicating that initialization has finished.  Or,
+	   wait a default of 15 seconds for that to happen and, if it doesn't
+	   just grab the lock ourselves. */
+	while ((val = InterlockedExchange (locker, -1)) == -1
+	       && (time () - then) < timeout)
+	  yield ();
+	/* Reset the lock back to wanted_value under the assumption that is
+	   what caused the above loop to kick out.  */
+	if (val == -1)
+	  val = 0;	/* Timed out.  We'll initialize things ourselves. */
+	else
+	  done (val);	/* Put back whatever was there before, assuming that
+			   it is actually wanted_val. */
+      }
+  }
+  ~spinlock () {done (setto);}
+  operator ULONG () const {return (ULONG) val;}
+  /* FIXME: This should be handled in a more general fashion, probably by
+     establishing a linked list of spinlocks which are freed on process exit. */
+  void multiple_cygwin_problem (const char *w, unsigned m, unsigned v)
+  {
+    done (val);
+    ::multiple_cygwin_problem (w, m, v);
+  }
+};
+
+#endif /*_SPINLOCK_H*/