diff --git a/api/boinc_api.C b/api/boinc_api.C
index 6b5b862804..258561d75a 100644
--- a/api/boinc_api.C
+++ b/api/boinc_api.C
@@ -534,6 +534,7 @@ int boinc_wu_cpu_time(double& cpu_t) {
 //
 int suspend_activities() {
     BOINCINFO("Received Suspend Message");
+	//fprintf(stderr, "suspending; %f %d\n", last_wu_cpu_time, options.direct_process_action);
 #ifdef _WIN32
     if (options.direct_process_action) {
         // in Windows this is called from a separate "timer thread",
@@ -550,6 +551,7 @@ int suspend_activities() {
 int resume_activities() {
     BOINCINFO("Received Resume Message");
 #ifdef _WIN32
+	//fprintf(stderr, "resuming; %f %d\n", last_wu_cpu_time, options.direct_process_action);
     if (options.direct_process_action) {
         // in Windows this is called from a separate "timer thread",
         // and Windows lets us resume the worker thread
@@ -644,6 +646,7 @@ static void handle_trickle_down_msg() {
 static void handle_process_control_msg() {
     char buf[MSG_CHANNEL_SIZE];
     if (app_client_shm->shm->process_control_request.get_msg(buf)) {
+		//fprintf(stderr, "%f: got %s\n", dtime(), buf);
         if (match_tag(buf, "<suspend/>")) {
             boinc_status.suspended = true;
             suspend_activities();
@@ -693,6 +696,7 @@ static void worker_timer(int /*a*/) {
         }
     }
 
+	//fprintf(stderr, "worker_timer: in_critical_section %d\n", in_critical_section);
     // handle messages from the core client
     //
     if (app_client_shm) {
diff --git a/checkin_notes b/checkin_notes
index a384fde8f2..90a293e3d6 100755
--- a/checkin_notes
+++ b/checkin_notes
@@ -12752,3 +12752,58 @@ Rom    20 Nov 2006
         BOINCTaskBar.cpp
         sg_CustomControls.cpp, .h
         sg_ProjectsComponent.cpp
+
+David  20 Nov 2006
+	- core client: fix a bug in the shared-memory message passing code.
+		Each message channel has a one-message buffer in shared mem.
+		The send_msg() function checks if this is full.
+		If not it puts the message there.
+		If so it stores the message in a queue.
+		Once a second, a poll function moves a message
+		from the queue to the buffer (if it's empty).
+
+		What's wrong with this? (let's not always see the same hands).
+		Well, the send_msg() needs to handle the situation
+		where there's a message in the queue but none in the buffer.
+
+		This results in a bug in the CPU throttling mechanism
+		that can cause a task to sleep forever.
+	- core client: a SECOND significant bug in the shmem msg passing code.
+		In general, the API library consumes at most one message per second
+		from a given channel.
+		That means that if you write more than one message/sec
+		(even for a short period) it creates a queue that never goes away.
+		If you write more than one message/sec indefinitely,
+		it creates an unbounded queue.
+
+		At this point, the only channel that uses queuing and can
+		have more than one msg/sec is process control
+		(because of CPU throttling).
+		I put in kludge that handles this case:
+		if we want to send a <resume/> and there's already
+		a <suspend/> in the queue,
+		remove the <suspend/> and don't send anything.
+		And conversely.
+	- core client: to debug all the above, added <app_msg_send>
+		and <app_msg_receive> log flags.
+		Also added some commented-out printfs in the API library.
+
+	NOTE: in the course of debugging this I realized that, in the Windows
+		version of the API, <suspend/> and <resume/> message result
+		in calls to SuspendThread() and ResumeThread(),
+		which inc and dec a "suspend counter".
+		ResumeThread() decrements the counter, and resumes the thread
+		only if the counter is then zero.
+		This makes the process-control message-passing scheme fragile.
+		If for some reason you send two <suspend/>s and a <resume/>,
+		the net result is suspended.
+		At some point we should change to API to do the right thing.
+
+	api/
+		boinc_api.C
+	client/
+		app.C
+		app_control.C
+		log_flags.C,h
+	lib/
+		app_ipc.h
diff --git a/client/app.C b/client/app.C
index 45ff53b69a..26e39ba340 100644
--- a/client/app.C
+++ b/client/app.C
@@ -577,22 +577,56 @@ int ACTIVE_TASK_SET::parse(MIOFILE& fin) {
 }
 
 void MSG_QUEUE::msg_queue_send(const char* msg, MSG_CHANNEL& channel) {
-    if (channel.send_msg(msg)) {
-        //msg_printf(NULL, MSG_INFO, "sent %s to %s", msg, name);
+    if ((msgs.size()==0) && channel.send_msg(msg)) {
+		if (log_flags.app_msg_send) {
+            msg_printf(NULL, MSG_INFO, "[app_msg_send] sent %s to %s", msg, name);
+		}
         return;
     }
+	if (log_flags.app_msg_send) {
+        msg_printf(NULL, MSG_INFO, "[app_msg_send] deferred %s to %s", msg, name);
+	}
     msgs.push_back(std::string(msg));
 }
 
 void MSG_QUEUE::msg_queue_poll(MSG_CHANNEL& channel) {
     if (msgs.size() > 0) {
+		if (log_flags.app_msg_send) {
+			msg_printf(NULL, MSG_INFO, "[app_msg_send] poll: %d msgs queued", msgs.size());
+		}
         if (channel.send_msg(msgs[0].c_str())) {
-            //msg_printf(NULL, MSG_INFO, "sent %s to %s (delayed)", (msgs[0].c_str()), name);
+			if (log_flags.app_msg_send) {
+				msg_printf(NULL, MSG_INFO, "[app_msg_send] poll: delayed sent %s to %s", (msgs[0].c_str()), name);
+			}
             msgs.erase(msgs.begin());
-        }
+		} else {
+			if (log_flags.app_msg_send) {
+				msg_printf(NULL, MSG_INFO, "[app_msg_send] poll: still deferred: %s to %s", (msgs[0].c_str()), name);
+			}
+		}
     }
 }
 
+// delete any queued messages with the given string
+//
+int MSG_QUEUE::msg_queue_purge(const char* msg) {
+	vector<string>::iterator iter = msgs.begin();
+	int count = 0;
+	while (iter != msgs.end()) {
+		if (!strcmp(msg, iter->c_str())) {
+			if (log_flags.app_msg_send) {
+				msg_printf(NULL, MSG_INFO, "[app_msg_send] purged %s", msg);
+			}
+			iter = msgs.erase(iter);
+			count++;
+		} else {
+			iter++;
+		}
+	}
+	return count;
+}
+
+
 void ACTIVE_TASK_SET::report_overdue() {
     unsigned int i;
     ACTIVE_TASK* atp;
diff --git a/client/app_control.C b/client/app_control.C
index e18552b88b..62c2fa4f16 100644
--- a/client/app_control.C
+++ b/client/app_control.C
@@ -800,10 +800,16 @@ void ACTIVE_TASK_SET::kill_tasks(PROJECT* proj) {
 //
 int ACTIVE_TASK::suspend() {
     if (!app_client_shm.shm) return 0;
-    process_control_queue.msg_queue_send(
-        "<suspend/>",
-        app_client_shm.shm->process_control_request
-    );
+	if (task_state != PROCESS_EXECUTING) {
+		msg_printf(0, MSG_INFO, "Internal error: expected process to be executing");
+	}
+	int n = process_control_queue.msg_queue_purge("<resume/>");
+	if (n == 0) {
+		process_control_queue.msg_queue_send(
+			"<suspend/>",
+			app_client_shm.shm->process_control_request
+		);
+	}
     task_state = PROCESS_SUSPENDED;
     return 0;
 }
@@ -812,13 +818,19 @@ int ACTIVE_TASK::suspend() {
 //
 int ACTIVE_TASK::unsuspend() {
     if (!app_client_shm.shm) return 0;
+	if (task_state != PROCESS_SUSPENDED) {
+		msg_printf(0, MSG_INFO, "Internal error: expected process to be suspended");
+	}
     if (log_flags.cpu_sched) {
         msg_printf(0, MSG_INFO, "[cpu_sched] Resuming %s", result->name);
     }
-    process_control_queue.msg_queue_send(
-        "<resume/>",
-        app_client_shm.shm->process_control_request
-    );
+	int n = process_control_queue.msg_queue_purge("<suspend/>");
+	if (n == 0) {
+		process_control_queue.msg_queue_send(
+			"<resume/>",
+			app_client_shm.shm->process_control_request
+		);
+	}
     task_state = PROCESS_EXECUTING;
     return 0;
 }
@@ -849,9 +861,9 @@ bool ACTIVE_TASK::get_app_status_msg() {
     if (!app_client_shm.shm->app_status.get_msg(msg_buf)) {
         return false;
     }
-    if (log_flags.app_msg_debug) {
+    if (log_flags.app_msg_receive) {
         msg_printf(NULL, MSG_INFO,
-            "[app_msg_debug] slot %d msg: %s", slot, msg_buf
+            "[app_msg_receive] got msg from slot %d: %s", slot, msg_buf
         );
     }
     want_network = 0;
diff --git a/client/log_flags.C b/client/log_flags.C
index 3e2f69a17e..c230830bb8 100644
--- a/client/log_flags.C
+++ b/client/log_flags.C
@@ -87,7 +87,8 @@ int LOG_FLAGS::parse(XML_PARSER& xp) {
         else if (xp.parse_bool(tag, "poll_debug", poll_debug)) continue;
         else if (xp.parse_bool(tag, "guirpc_debug", guirpc_debug)) continue;
         else if (xp.parse_bool(tag, "scrsave_debug", scrsave_debug)) continue;
-        else if (xp.parse_bool(tag, "app_msg_debug", app_msg_debug)) continue;
+        else if (xp.parse_bool(tag, "app_msg_send", app_msg_send)) continue;
+        else if (xp.parse_bool(tag, "app_msg_receive", app_msg_receive)) continue;
         else if (xp.parse_bool(tag, "mem_usage_debug", mem_usage_debug)) continue;
         else if (xp.parse_bool(tag, "network_status_debug", network_status_debug)) continue;
         else {
@@ -138,7 +139,8 @@ void LOG_FLAGS::show() {
     show_flag(buf, poll_debug, "poll_debug");
     show_flag(buf, guirpc_debug, "guirpc_debug");
     show_flag(buf, scrsave_debug, "scrsave_debug");
-    show_flag(buf, app_msg_debug, "app_msg_debug");
+    show_flag(buf, app_msg_send, "app_msg_send");
+    show_flag(buf, app_msg_receive, "app_msg_receive");
     show_flag(buf, mem_usage_debug, "mem_usage_debug");
     show_flag(buf, network_status_debug, "network_status_debug");
     if (strlen(buf)) {
diff --git a/client/log_flags.h b/client/log_flags.h
index 1d9855cd13..7e613c8b73 100644
--- a/client/log_flags.h
+++ b/client/log_flags.h
@@ -64,7 +64,8 @@ struct LOG_FLAGS {
     bool poll_debug;        // show what polls are responding
     bool guirpc_debug;
     bool scrsave_debug;
-    bool app_msg_debug;     // show shared-mem message from apps
+    bool app_msg_send;       // show shared-mem message to apps
+    bool app_msg_receive;    // show shared-mem message from apps
 	bool mem_usage_debug;	// memory usage
 	bool network_status_debug;
 
diff --git a/lib/app_ipc.h b/lib/app_ipc.h
index 87dad4eb1c..c67ac92e4e 100755
--- a/lib/app_ipc.h
+++ b/lib/app_ipc.h
@@ -109,6 +109,7 @@ struct MSG_QUEUE {
     char name[256];
     void msg_queue_send(const char*, MSG_CHANNEL& channel);
     void msg_queue_poll(MSG_CHANNEL& channel);
+	int msg_queue_purge(const char*);
 };
 
 #define DEFAULT_FRACTION_DONE_UPDATE_PERIOD     1