Promote domains and Cyclone library to entities

This commit adds two entity types: a "domain", which is the parent of
participants and which is instantiated for each domain that has at least
one participant in it; and "cyclonedds", which is a representation of
the (initialized) Cyclone DDS library in the process and that is the
parent of all domain entities.  The handle of the latter is a
compile-constant, DDS_CYCLONEDDS_HANDLE.

This changes the return value from dds_get_parent when executed on a
participant: it now returns the handle of the entity representing the
domain the participant is attached to.  Two participants in the same
domain self-evidently return the same domain entity.

This allows deleting all participants in a domain by calling dds_delete
on the domain entity, or tearing down everything and deinitializing the
library by calling dds_delete on the top-level entity.

Signed-off-by: Erik Boasson <eb@ilities.com>

src/ddsrt/include/dds/ddsrt/cdtors.h

@@ -25,6 +25,8 @@ DDS_EXPORT void ddsrt_fini(void);
 
 DDS_EXPORT ddsrt_mutex_t *ddsrt_get_singleton_mutex(void);
 
+DDS_EXPORT ddsrt_cond_t *ddsrt_get_singleton_cond(void);
+
 #if defined (__cplusplus)
 }
 #endif

src/ddsrt/src/cdtors.c

@@ -28,6 +28,7 @@ extern void ddsrt_time_fini(void);
 #define INIT_STATUS_OK 0x80000000u
 static ddsrt_atomic_uint32_t init_status = DDSRT_ATOMIC_UINT32_INIT(0);
 static ddsrt_mutex_t init_mutex;
+static ddsrt_cond_t init_cond;
 
 void ddsrt_init (void)
 {
@@ -38,6 +39,7 @@ retry:
     return;
   else if (v == 1) {
     ddsrt_mutex_init(&init_mutex);
+    ddsrt_cond_init(&init_cond);
 #if _WIN32
     ddsrt_winsock_init();
     ddsrt_time_init();
@@ -67,6 +69,7 @@ void ddsrt_fini (void)
   } while (!ddsrt_atomic_cas32(&init_status, v, nv));
   if (nv == 1)
   {
+    ddsrt_cond_destroy(&init_cond);
     ddsrt_mutex_destroy(&init_mutex);
     ddsrt_random_fini();
     ddsrt_atomics_fini();
@@ -83,6 +86,11 @@ ddsrt_mutex_t *ddsrt_get_singleton_mutex(void)
   return &init_mutex;
 }
 
+ddsrt_cond_t *ddsrt_get_singleton_cond(void)
+{
+  return &init_cond;
+}
+
 #ifdef _WIN32
 #include "dds/ddsrt/threads.h"