* tsd.c: Add comment explaining rationale for not building

        POSIX TSD on top of Win32 TLS.

2 files changed, 20 insertions, 0 deletions

diff --git a/ChangeLog b/ChangeLog
index 6cece62..34e6b71 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -7,6 +7,9 @@
 Sat Sep 12 20:09:24 1998  Ross Johnson  <rpj@ixobrychus.canberra.edu.au>
 
 	* windows.h: Remove error number definitions. These are in <errno.h>
+	
+	* tsd.c: Add comment explaining rationale for not building
+	POSIX TSD on top of Win32 TLS.
 
 1998-09-12  Ben Elliston  <bje@cygnus.com>
 
diff --git a/tsd.c b/tsd.c
index 02069a9..015af85 100644
--- a/tsd.c
+++ b/tsd.c
@@ -4,6 +4,23 @@
  * Description:
  * POSIX thread functions which implement thread-specific data (TSD).
  */
+ 
+/*
+ * Why we can't use Win32 TLS
+ * --------------------------
+ *
+ * In a word: Destructors
+ *
+ * POSIX 1003.1 1996, Section 17 allows for optional destructor functions
+ * to be associated with each key value. The destructors are called from
+ * the creating thread, which means that the calling thread must have access
+ * to the TSD keys of all active threads.
+ *
+ * If we use Win32 TLS then this is not possible since Tls*Value()
+ * functions don't allow us to access other than our own [thread's] key.
+ *
+ * As a result, these routines need to be redesigned.
+ */
 
 #include <errno.h>