X-Git-Url: https://git.carlh.net/gitweb/?a=blobdiff_plain;f=libs%2Fpbd%2Fevent_loop.cc;h=3f5eeb0a755d3c9325fa2aa4a5162d0bf1ea8d04;hb=9ab92a67c856e371b292d701f2068207efe79af3;hp=11177610030e9a694d6711961715bfac1e10f1ca;hpb=d3ad5c16d13847dadb7821e6c3f225261d4b04ce;p=ardour.git

diff --git a/libs/pbd/event_loop.cc b/libs/pbd/event_loop.cc
index 1117761003..3f5eeb0a75 100644
--- a/libs/pbd/event_loop.cc
+++ b/libs/pbd/event_loop.cc
@@ -17,6 +17,10 @@
 
 */
 
+#include <cstring>
+
+#include <pthread.h>
+
 #include "pbd/compose.h"
 #include "pbd/debug.h"
 #include "pbd/event_loop.h"
@@ -171,24 +175,59 @@ EventLoop::pre_register (const string& emitting_thread_name, uint32_t num_reques
 		   AbstractUI constructor. Note that if
 		*/
 
-		/* make a key composed of the emitter and receiver thread names */
-
-		string key = emitting_thread_name;
-		key += '/';
-		key +=  mapping.target_thread_name;
+		const string key = string_compose ("%1/%2", emitting_thread_name, mapping.target_thread_name);
 
-		/* if the emitting thread was killed and recreated (with the
-		 * same name), this will replace the entry in
-		 * thread_buffer_requests. The old entry will be lazily deleted
-		 * when the target thread finds the request buffer and realizes
-		 * that it is dead.
+		/* management of the thread_request_buffers map works as
+		 * follows:
 		 *
-		 * If the request buffer is replaced before the target thread
-		 * ever finds the dead version, we will leak the old request
-		 * buffer.
+		 * when the factory method was called above, the pointer to the
+		 * created buffer is set as a thread-local-storage (TLS) value
+		 * for this (the emitting) thread.
+		 *
+		 * The TLS value is set up with a destructor that marks the
+		 * request buffer as "dead" when the emitting thread exits.
+		 *
+		 * An entry will remain in the map after the thread exits.
+		 *
+		 * The receiving thread may (if it receives requests from other
+		 * threads) notice the dead buffer. If it does, it will delete
+		 * the request buffer, and call
+		 * ::remove_request_buffer_from_map() to get rid of it from the map.
+		 *
+		 * This does mean that the lifetime of the request buffer is
+		 * indeterminate: if the receiving thread were to receive no
+		 * further requests, the request buffer will live on
+		 * forever. But this is OK, because if there are no requests
+		 * arriving, the receiving thread is not attempting to use the
+		 * request buffer(s) in any way.
+		 *
+		 * Note, however, that *if* an emitting thread is recreated
+		 * with the same name (e.g. when a control surface is
+		 * enabled/disabled/enabled), then the request buffer for the
+		 * new thread will replace the map entry for the key, because
+		 * of the matching thread names. This does mean that
+		 * potentially the request buffer can leak in this case, but
+		 * (a) these buffers are not really that large anyway (b) the
+		 * scenario is not particularly common (c) the buffers would
+		 * typically last across a session instance if not program
+		 * lifetime anyway.
 		 */
 
 		thread_buffer_requests[key] = mapping;
-		DEBUG_TRACE (PBD::DEBUG::EventLoop, string_compose ("pre-registered request buffer for \"%1\" to send to \"%2\", buffer @ %3\n", emitting_thread_name, trs->name, mapping.request_buffer));
+		DEBUG_TRACE (PBD::DEBUG::EventLoop, string_compose ("pre-registered request buffer for \"%1\" to send to \"%2\", buffer @ %3 (key was %4)\n",
+		                                                    emitting_thread_name, trs->name, mapping.request_buffer, key));
+	}
+}
+
+void
+EventLoop::remove_request_buffer_from_map (void* ptr)
+{
+	Glib::Threads::RWLock::WriterLock lm (thread_buffer_requests_lock);
+
+	for (ThreadRequestBufferList::iterator x = thread_buffer_requests.begin(); x != thread_buffer_requests.end(); ++x) {
+		if (x->second.request_buffer == ptr) {
+			thread_buffer_requests.erase (x);
+			break;
+		}
 	}
 }