From a9ff3dc41192afa82e052a8550725cf74bf13cf2 Mon Sep 17 00:00:00 2001
From: Gareth Rees <gdr@ravenbrook.com>
Date: Wed, 27 Jun 2018 14:53:21 +0100
Subject: [PATCH 1/2] Branching master to branch/2018-06-27/job004056.

Copied from Perforce
 Change: 194240

From b6b66edf9be7e861587dfd50495d810c8197f631 Mon Sep 17 00:00:00 2001
From: Gareth Rees <gdr@ravenbrook.com>
Date: Thu, 28 Jun 2018 12:39:06 +0100
Subject: [PATCH 2/2] Use initonceexecuteonce to get thread-safe initialization
 of the global locks.

This means that the MPS no longer supports Windows XP, so update documentation accordingly.
Exercise the global locks in lockut.

Copied from Perforce
 Change: 194253
---
 mps/code/lockut.c                    |  7 +++++++
 mps/code/lockw3.c                    | 25 ++++++++++++++++++++++---
 mps/manual/source/guide/overview.rst |  3 ++-
 mps/manual/source/release.rst        |  9 +++++++++
 mps/readme.txt                       |  3 ++-
 5 files changed, 42 insertions(+), 5 deletions(-)

diff --git a/mps/code/lockut.c b/mps/code/lockut.c
index a6e592988f1..9f9637914f0 100644
--- a/mps/code/lockut.c
+++ b/mps/code/lockut.c
@@ -57,7 +57,14 @@ static void inc(unsigned long i)
 #define COUNT 100000l
 static void *thread0(void *p)
 {
+  unsigned i;
   testlib_unused(p);
+  LockClaimGlobal();
+  LockReleaseGlobal();
+  for (i = 0; i < COUNT; ++i)
+    LockClaimGlobalRecursive();
+  for (i = 0; i < COUNT; ++i)
+    LockReleaseGlobalRecursive();
   inc(COUNT);
   return NULL;
 }
diff --git a/mps/code/lockw3.c b/mps/code/lockw3.c
index a2266542158..ba177c6b68b 100644
--- a/mps/code/lockw3.c
+++ b/mps/code/lockw3.c
@@ -136,13 +136,32 @@ void LockInitGlobal(void)
   globalLockInit = TRUE;
 }
 
-static void lockEnsureGlobalLock(void)
+/* lockEnsureGlobalLock -- one-time initialization of global locks
+ *
+ * InitOnceExecuteOnce ensures that only one thread can be running the
+ * callback at a time, which allows to safely check globalLockInit. See
+ * <https://docs.microsoft.com/en-us/windows/desktop/api/synchapi/nf-synchapi-initonceexecuteonce>
+ * but note that at time of writing (2018-06-27) the documentation has
+ * the arguments the wrong way round (parameter comes before context).
+ */
+
+static BOOL CALLBACK lockEnsureGlobalLockCallback(INIT_ONCE *init_once, void *parameter, void **context)
 {
-  /* Ensure both global locks have been initialized. */
-  /* There is a race condition initializing them (job004056). */
+  UNUSED(init_once);
+  AVER(parameter == UNUSED_POINTER);
+  UNUSED(context);
   if (!globalLockInit) {
     LockInitGlobal();
   }
+  return TRUE;
+}
+
+static void lockEnsureGlobalLock(void)
+{
+  static INIT_ONCE init_once = INIT_ONCE_STATIC_INIT;
+  BOOL b = InitOnceExecuteOnce(&init_once, lockEnsureGlobalLockCallback,
+                               UNUSED_POINTER, NULL);
+  AVER(b);
 }
 
 void (LockClaimGlobalRecursive)(void)
diff --git a/mps/manual/source/guide/overview.rst b/mps/manual/source/guide/overview.rst
index 116843e9697..c813aaf34c4 100644
--- a/mps/manual/source/guide/overview.rst
+++ b/mps/manual/source/guide/overview.rst
@@ -50,7 +50,8 @@ Supported target platforms
 
 The MPS is currently supported for deployment on:
 
-- Windows XP or later, on IA-32 and x86-64, using Microsoft Visual C/C++;
+- Windows Vista or later, on IA-32 and x86-64, using Microsoft Visual
+  C/C++;
 
 - Linux 2.6 or later, on IA-32 using GCC and on x86-64 using GCC or
   Clang/LLVM;
diff --git a/mps/manual/source/release.rst b/mps/manual/source/release.rst
index bdde9d1e04d..ed92bbc085f 100644
--- a/mps/manual/source/release.rst
+++ b/mps/manual/source/release.rst
@@ -15,6 +15,15 @@ New features
 #. On FreeBSD, Linux and macOS, the MPS is now able to run in the
    child process after ``fork()``. See :ref:`topic-thread-fork`.
 
+#. The MPS now supports Windows Vista or later; it no longer supports
+   Windows XP. (Microsoft's own support for Windows XP `expired in
+   April 2014`_.) This is so that we can use |InitOnceExecuteOnce|_ to
+   ensure thread-safe initialization.
+
+   .. _expired in April 2014: https://www.microsoft.com/en-gb/windowsforbusiness/end-of-xp-support
+   .. |InitOnceExecuteOnce| replace:: ``InitOnceExecuteOnce()``
+   .. _InitOnceExecuteOnce: https://docs.microsoft.com/en-us/windows/desktop/api/synchapi/nf-synchapi-initonceexecuteonce
+
 
 .. _release-notes-1.116:
 
diff --git a/mps/readme.txt b/mps/readme.txt
index 747abcc727c..115ec3d01d3 100644
--- a/mps/readme.txt
+++ b/mps/readme.txt
@@ -72,7 +72,8 @@ Supported target platforms
 
 The MPS is currently supported for deployment on:
 
-- Windows XP or later, on IA-32 and x86-64, using Microsoft Visual C/C++;
+- Windows Vista or later, on IA-32 and x86-64, using Microsoft Visual
+  C/C++;
 
 - Linux 2.6 or later, on IA-32 using GCC and on x86-64 using GCC or
   Clang/LLVM;