Threading API additions for acquired monitors

API additions expose details about acquired monitors such as owner, number of times acquired, and information about waiting threads. May be useful for runtimes that require specific information about the state of acquired monitors such in Eclipse OpenJ9 snapshot+restore.

Signed-off-by: Theresa Mammarella <tmammare@redhat.com>

include_core/thread_api.h

@@ -533,6 +533,41 @@ omrthread_global(char *name);
 omrthread_monitor_t
 omrthread_global_monitor(void);
 
+/**
+ * Return monitor that thread is currently waiting to acquire. 
+ * If thread is not waiting on a monitor return null.
+ * @param thread
+ * @return omrthread_monitor_t
+ */
+omrthread_monitor_t
+omrthread_waiting_to_acquire(omrthread_t thread);
+
+/**
+ * Return true if monitor is currently acquired.
+ * @param monitor
+ * @return BOOLEAN
+ */
+BOOLEAN
+omrthread_monitor_is_acquired(omrthread_monitor_t monitor);
+
+/**
+ * Monitor may be acquired multiple times by the current owner.
+ * Return number of times it has been acquired. Zero means
+ * the monitor is not acquired.
+ * @param monitor
+ * @return intptr_t
+ */
+intptr_t
+omrthread_monitor_get_acquired_count(omrthread_monitor_t monitor);
+
+/**
+ * Return thread that currently owns the monitor. Null 
+ * will be returned if monitor is not owned.
+ * @param monitor
+ * @return omrthread_t
+ */
+omrthread_t
+omrthread_monitor_get_current_owner(omrthread_monitor_t monitor);
 
 /**
 * @brief

thread/common/omrthread.c

@@ -1219,6 +1219,25 @@ omrthread_global_monitor(void)
 	return lib->globalMonitor;
 }
 
+omrthread_monitor_t
+omrthread_waiting_to_acquire(omrthread_t thread) {
+	return thread->monitor;
+}
+
+BOOLEAN
+omrthread_monitor_is_acquired(omrthread_monitor_t monitor) {
+	return (monitor->count > 0);
+}
+
+intptr_t
+omrthread_monitor_get_acquired_count(omrthread_monitor_t monitor) {
+	return monitor->count;
+}
+
+omrthread_t
+omrthread_monitor_get_current_owner(omrthread_monitor_t monitor) {
+	return monitor->owner;
+}
 
 /*
  * Threads
@@ -1839,7 +1858,7 @@ omrthread_exit(omrthread_monitor_t monitor)
 /**
  * Create a new OS thread and attach it to the library.
  *
- * @param[out] handle
+ * @param[out] handle Location where the new omrthread_t should be returned, if successfully created. May be NULL.
  * @param[in] attr attr must not be modified by this function.
  * @param[in] suspend Non-zero if the thread should suspend before entering entrypoint,
  * zero to allow the thread to run freely.
@@ -5906,4 +5925,3 @@ j9thread_tls_get(omrthread_t thread, omrthread_tls_key_t key)
 {
 	return omrthread_tls_get(thread, key);
 }
-

thread/exports.cmake

@@ -33,6 +33,10 @@ omr_add_exports(j9thr_obj
 	omrthread_abort
 	omrthread_attach
 	omrthread_attach_ex
+	omrthread_waiting_to_acquire
+	omrthread_monitor_is_acquired
+	omrthread_monitor_get_acquired_count
+	omrthread_monitor_get_current_owner
 	omrthread_create
 	omrthread_create_ex
 	omrthread_cancel

thread/thread_include.mk

@@ -141,6 +141,10 @@ define WRITE_COMMON_THREAD_EXPORTS
 @echo omrthread_abort >>$@
 @echo omrthread_attach >>$@
 @echo omrthread_attach_ex >>$@
+@echo omrthread_waiting_to_acquire >>$@
+@echo omrthread_monitor_is_acquired >>$@
+@echo omrthread_monitor_get_acquired_count >>$@
+@echo omrthread_monitor_get_current_owner >>$@
 @echo omrthread_create >>$@
 @echo omrthread_create_ex >>$@
 @echo omrthread_cancel >>$@