From b7903bcedc478cd36377e5e3c58203a16530d3e2 Mon Sep 17 00:00:00 2001
From: Jeff Squyres <jsquyres@cisco.com>
Date: Tue, 13 Jan 2004 23:32:19 +0000
Subject: [PATCH] Added doxygen comments.

This commit was SVN r339.
---
 src/lam/threads/mutex.h | 123 ++++++++++++++++++++++++++++++++++++----
 1 file changed, 113 insertions(+), 10 deletions(-)

diff --git a/src/lam/threads/mutex.h b/src/lam/threads/mutex.h
index aff0d5549e..53b110854b 100644
--- a/src/lam/threads/mutex.h
+++ b/src/lam/threads/mutex.h
@@ -2,8 +2,8 @@
  * $HEADER$
  */
 
-#ifndef _MUTEX_H_
-#define _MUTEX_H_
+#ifndef LAM_MUTEX_H_
+#define LAM_MUTEX_H_
 
 #include "lam_config.h"
 
@@ -13,26 +13,129 @@
 #include "lam/threads/mutex_spinlock.h"
 #endif
 
-static inline bool lam_use_threads(void) 
+/**
+ * Check and see if the process is using multiple threads.
+ *
+ * @retval true If the process may have more than one thread.
+ * @retval false If the process only has a single thread.
+ *
+ * The value that this function returns is influenced by:
+ *
+ * - how MPI_INIT or MPI_INIT_THREAD was invoked, 
+ * - what the final MPI thread level was determined to be,
+ * - whether the LAM or MPI libraries are multi-threaded (Jan 2003:
+ *   they're not),
+ * - whether configure determined if we have thread support or not
+ *
+ * MPI_INIT and MPI_INIT_THREAD (specifically, back-end LAM startup
+ * functions) invoke lam_set_using_threads() to influence the value of
+ * this function, depending on their situation. Some examples:
+ *
+ * - if configure determined that we do not have threads, then this
+ * value will always be false.
+ *
+ * - if MPI_INIT is invoked, and the lam/mpi libraries are [still]
+ * single-threaded, this value will be false.
+ *
+ * - if MPI_INIT_THREAD is invoked with MPI_THREAD_MULTIPLE, we have
+ * thread support, and the final thread level is determined to be
+ * MPI_THREAD_MULTIPLE, this value will be true.
+ *
+ * - if the process is a single-threaded LAM executable (e.g., mpicc),
+ * this value will be false.
+ *
+ * Hence, this function will return false if there is guaranteed to
+ * only be one thread in the process.  If there is even the
+ * possibility that we may have multiple threads, true will be
+ * returned.
+ */
+static inline bool lam_using_threads(void) 
 { 
     extern bool lam_uses_threads;
     return lam_uses_threads; 
 }
 
-/*
- * Lock macros
+/**
+ * Set whether the process is using multiple threads or not.
+ *
+ * @param have Boolean indicating whether the process is using
+ * multiple threads or not.
+ *
+ * @retval lam_using_threads The new return value from
+ * lam_using_threads().
+ *
+ * This function is used to influence the return value of
+ * lam_using_threads().  If configure detected that we have thread
+ * support, the return value of future invocations of
+ * lam_using_threads() will be the parameter's value.  If configure
+ * detected that we have no thread support, then the retuen from
+ * lam_using_threads() will always be false.
  */
-#define THREAD_LOCK(a)   if(lam_use_threads()) \
+static inline bool lam_set_using_threads(bool have) 
+{ 
+    extern bool lam_uses_threads;
+#if LAM_HAVE_THREADS
+    lam_uses_threads = have;
+#else
+    lam_uses_threads = false;
+#endif
+    return lam_uses_threads; 
+}
+
+/**
+ * Lock a mutex if lam_using_threads() says that multiple threads may
+ * be active in the process.
+ *
+ * @param mutex Pointer to a lam_mutex_t to lock.
+ *
+ * If there is a possibility that multiple threads are running in the
+ * process (as determined by lam_using_threads()), this function will
+ * block waiting to lock the mutex.
+ *
+ * If there is no possibility that multiple threads are running in the
+ * process, return immediately.
+ */
+#define THREAD_LOCK(a)   if (lam_using_threads()) \
                               lam_mutex_lock((a));
 
-#define LOCK(a)          lam_mutex_lock((a))
-
 /*
- * unlock macros
+ * Unlock a mutex if lam_using_threads() says that multiple threads
+ * may be active in the process.
+ *
+ * @param mutex Pointer to a lam_mutex_t to unlock.
+ *
+ * If there is a possibility that multiple threads are running in the
+ * process (as determined by lam_using_threads()), this function will
+ * unlock the mutex.
+ *
+ * If there is no possibility that multiple threads are running in the
+ * process, return immediately without modifying the mutex.
  */
-#define THREAD_UNLOCK(a) if(lam_use_threads()) \
+#define THREAD_UNLOCK(a) if (lam_using_threads()) \
                               lam_mutex_unlock((a));
 
+/**
+ * Always locks a mutex (never compile- or run-time removed)
+ *
+ * @param mutex A pointer to a lam_mutex_t.
+ *
+ * Locks the mutex.  This is the macro that you should use for mutexes
+ * that should always be locked, regardless of whether the process has
+ * multiple threads or not.  This is useful, for example, with shared
+ * memory.
+ */
+#define LOCK(a)          lam_mutex_lock((a))
+
+/**
+ * Always unlocks a mutex (never compile- or run-time removed)
+ *
+ * @param mutex A pointer to a lam_mutex_t.
+ *
+ * Unlocks the mutex.  This is the macro that you should use for
+ * mutexes that should always be unlocked, regardless of whether the
+ * process has multiple threads or not.  This is useful, for example,
+ * with shared memory.
+ */
 #define UNLOCK(a)        lam_mutex_unlock((a));
 
 #endif