From 5c27f5550c12edf7605d8714f6870f4a706bd500 Mon Sep 17 00:00:00 2001
From: Leif Andersen <leif@leifandersen.net>
Date: Mon, 5 Jun 2017 10:46:24 -0400
Subject: [PATCH] Add mzrt_sema_trywait to the mzrt library.

This commit add mzrt_sema_try_wait to the functions that operate
on semaphores. The existing ones are:

* int mzrt_sema_create(mzrt_sema **sema, int init);
* int mzrt_sema_post(mzrt_sema *sema);
* int mzrt_sema_wait(mzrt_sema *sema);
* int mzrt_sema_destroy(mzrt_sema *sema);
---
 racket/src/racket/src/mzrt.c | 17 +++++++++++++++++
 racket/src/racket/src/mzrt.h |  1 +
 2 files changed, 18 insertions(+)

diff --git a/racket/src/racket/src/mzrt.c b/racket/src/racket/src/mzrt.c
index 1807d69b6c..c351b27ee9 100644
--- a/racket/src/racket/src/mzrt.c
+++ b/racket/src/racket/src/mzrt.c
@@ -598,6 +598,18 @@ int mzrt_sema_wait(mzrt_sema *s)
   return 0;
 }
 
+int mzrt_sema_trywait(mzrt_sema *s)
+{
+  int locked = 1;
+  pthread_mutex_lock(&s->m);
+  if(s->ready) {
+    --s->ready;
+    locked = 0;
+  }
+  pthread_mutex_unlock(&s->m);
+  return locked;
+}
+
 int mzrt_sema_post(mzrt_sema *s)
 {
   pthread_mutex_lock(&s->m);
@@ -810,6 +822,11 @@ int mzrt_sema_wait(mzrt_sema *s)
   return 0;
 }
 
+int mzrt_sema_trywait(mzrt_sema *s)
+{
+  return WaitForSingleObject(s->ws, 0);
+}
+
 int mzrt_sema_post(mzrt_sema *s)
 {
   ReleaseSemaphore(s->ws, 1, NULL);  
diff --git a/racket/src/racket/src/mzrt.h b/racket/src/racket/src/mzrt.h
index 2eee24a79a..163025921b 100644
--- a/racket/src/racket/src/mzrt.h
+++ b/racket/src/racket/src/mzrt.h
@@ -86,6 +86,7 @@ typedef struct mzrt_sema mzrt_sema; /* OPAQUE DEFINITION */
 int mzrt_sema_create(mzrt_sema **sema, int init);
 int mzrt_sema_post(mzrt_sema *sema);
 int mzrt_sema_wait(mzrt_sema *sema);
+int mzrt_sema_trywait(mzrt_sema *sema);
 int mzrt_sema_destroy(mzrt_sema *sema);
 
 /****************** Compare and Swap *******************************/