2001-05-14 Till Straumann <strauman@slac.stanford.edu>

	* Per PR212, added envlock support for newlib.  This is used
	by at least getenv()/putenv() to avoid race conditions.
	* libc/envlock.c: New file.
	* libc/Makefile.am: Modified to reflect above.

1 files changed, 82 insertions, 0 deletions

diff --git a/c/src/lib/libc/envlock.c b/c/src/lib/libc/envlock.c
new file mode 100644
index 0000000000..c9489b3e88
--- /dev/null
+++ b/c/src/lib/libc/envlock.c
@@ -0,0 +1,82 @@
+/*
+ *  $Id$
+ *
+ *  Author: Till Straumann <strauman@slac.stanford.edu>, 3/2002
+ */
+
+/* provide locking for the global environment 'environ' */
+
+#if HAVE_CONFIG_H
+#include "config.h"
+#endif
+
+#include <rtems.h>
+#include <sys/reent.h>
+
+#include <assert.h>
+
+/*
+ * NOTES:
+ *  - although it looks like a classical multiple-readers / single writer (MRSW)
+ *    locking problem, we still use a single lock for the following reasons:
+ *     1) newlib has no provision / hook for calling different locking routines
+ *        from setenv/putenv and getenv, respectively.
+ *     2) MRSW involves calling several semaphore-primitives, even in the most
+ *        likely case of a first-reader's access. This probably takes more CPU
+ *        time than just waiting until another reader is done; environment
+ *        access is fast.
+ *  - the lock implementation must allow nesting (same thread may call
+ *    lock-lock-unlock-unlock).
+ *  - NEWLIB-1.8.2 has an ugly BUG: if environ is NULL, _findenv_r() bails
+ *    out leaving the lock held :-(
+ *  
+ */
+
+static rtems_id envLock=0;
+
+static void
+__rtems_envlock_init(void)
+{
+  extern char        **environ;
+  rtems_status_code    rc;
+
+  if (envLock) /* already initialized */
+    return;
+
+  assert(environ && "MUST have non-NULL 'environ' due to newlib bug");
+
+  rc = rtems_semaphore_create(
+      rtems_build_name('E','N','V','S'),
+      1,
+      RTEMS_BINARY_SEMAPHORE | RTEMS_PRIORITY | RTEMS_INHERIT_PRIORITY,
+      0,
+      &envLock);
+  if (RTEMS_SUCCESSFUL!=rc)
+    rtems_fatal_error_occurred(rc);
+}
+
+void
+__env_lock(struct _reent *r)
+{
+  /* Do lazy init */
+  if (!envLock)
+    __rtems_envlock_init();
+  /*
+   *  Must not use a semaphore before pre-tasking hook is called.
+   *  - it will corrupt memory :-(
+   */
+
+  if (_Thread_Executing)
+    rtems_semaphore_obtain(envLock, RTEMS_WAIT, RTEMS_NO_TIMEOUT);
+}
+
+void
+__env_unlock(struct _reent *r)
+{
+  /*
+   *  Must not use a semaphore before pre-tasking hook is called.
+   * - it will corrupt memory :-(
+   */
+  if (_Thread_Executing)
+    rtems_semaphore_release(envLock);
+}