diff --git a/exec.cpp b/exec.cpp
index 85a3696a5..78d64695b 100644
--- a/exec.cpp
+++ b/exec.cpp
@@ -34,6 +34,7 @@
 
 #include "fallback.h"
 #include "util.h"
+#include "iothread.h"
 
 #include "common.h"
 #include "wutil.h"
@@ -833,6 +834,9 @@ static pid_t exec_fork()
 {
     ASSERT_IS_MAIN_THREAD();
     
+    /* Make sure we have no outstanding threads before we fork. This is a pretty sketchy thing to do here, both because exec.cpp shouldn't have to know about iothreads, and because the completion handlers may do unexpected things. */
+    iothread_drain_all();
+    
 	pid_t pid;
 	struct timespec pollint;
 	int i;
diff --git a/iothread.cpp b/iothread.cpp
index b98dd8f24..3aed2aadb 100644
--- a/iothread.cpp
+++ b/iothread.cpp
@@ -9,6 +9,7 @@
 #include <stdlib.h>
 #include <unistd.h>
 #include <signal.h>
+#include <queue>
 
 
 #define VOMIT_ON_FAILURE(a) do { if (0 != (a)) { int err = errno; fprintf(stderr, "%s failed on line %d in file %s: %d (%s)\n", #a, __LINE__, __FILE__, err, strerror(err)); abort(); }} while (0)
@@ -33,7 +34,6 @@ static struct WorkerThread_t {
 } threads[IO_MAX_THREADS];
 
 struct ThreadedRequest_t {
-	struct ThreadedRequest_t *next;
 	int sequenceNumber;
 	
 	int (*handler)(void *);
@@ -50,14 +50,14 @@ static struct WorkerThread_t *next_vacant_thread_slot(void) {
 }
 
 static pthread_mutex_t s_request_queue_lock;
-static struct ThreadedRequest_t *s_request_queue_head;
+static std::queue<ThreadedRequest_t *> s_request_queue;
 static int s_last_sequence_number;
 static int s_read_pipe, s_write_pipe;
 
 static void iothread_init(void) {
-	static int inited = 0;
+	static bool inited = false;
 	if (! inited) {
-		inited = 1;
+		inited = true;
 		
 		/* Initialize the queue lock */
 		VOMIT_ON_FAILURE(pthread_mutex_init(&s_request_queue_lock, NULL));
@@ -76,16 +76,18 @@ static void iothread_init(void) {
 }
 
 static void add_to_queue(struct ThreadedRequest_t *req) {
-	//requires that the queue lock be held
-	if (s_request_queue_head == NULL) {
-		s_request_queue_head = req;
-	} else {
-		struct ThreadedRequest_t *last_in_queue = s_request_queue_head;
-		while (last_in_queue->next != NULL) {
-			last_in_queue = last_in_queue->next;
-		}
-		last_in_queue->next = req;
-	}
+	ASSERT_IS_LOCKED(s_request_queue_lock);
+    s_request_queue.push(req);
+}
+
+static ThreadedRequest_t *dequeue_request(void) {
+    ThreadedRequest_t *result = NULL;
+    scoped_lock lock(s_request_queue_lock);
+    if (! s_request_queue.empty()) {
+        result = s_request_queue.front();
+        s_request_queue.pop();
+    }
+    return result;
 }
 
 /* The function that does thread work. */
@@ -99,13 +101,7 @@ static void *iothread_worker(void *threadPtr) {
     VOMIT_ON_FAILURE(pthread_sigmask(SIG_SETMASK, &set, NULL));
     
 	/* Grab a request off of the queue */
-	struct ThreadedRequest_t *req;
-	VOMIT_ON_FAILURE(pthread_mutex_lock(&s_request_queue_lock));
-	req = s_request_queue_head;
-	if (req) {
-		s_request_queue_head = req->next;
-	}
-	VOMIT_ON_FAILURE(pthread_mutex_unlock(&s_request_queue_lock));
+	struct ThreadedRequest_t *req = dequeue_request();
 
 	/* Run the handler and store the result */
 	if (req) {
@@ -121,7 +117,8 @@ static void *iothread_worker(void *threadPtr) {
 
 /* Spawn another thread if there's work to be done. */
 static void iothread_spawn_if_needed(void) {
-	if (s_request_queue_head != NULL && s_active_thread_count < IO_MAX_THREADS) {
+    ASSERT_IS_LOCKED(s_request_queue_lock);
+	if (! s_request_queue.empty() && s_active_thread_count < IO_MAX_THREADS) {
 		struct WorkerThread_t *thread = next_vacant_thread_slot();
 		assert(thread != NULL);
 		
@@ -147,24 +144,19 @@ int iothread_perform_base(int (*handler)(void *), void (*completionCallback)(voi
 	
 	/* Create and initialize a request. */
 	struct ThreadedRequest_t *req = new ThreadedRequest_t();
-	req->next = NULL;
 	req->handler = handler;
 	req->completionCallback = completionCallback;
 	req->context = context;
 	req->sequenceNumber = ++s_last_sequence_number;
-	
-	/* Take the queue lock */
-	VOMIT_ON_FAILURE(pthread_mutex_lock(&s_request_queue_lock));
-	
-	/* Add to the queue */
-	add_to_queue(req);
-	
-	/* Spawn a thread if necessary */
-	iothread_spawn_if_needed();
-	
-	/* Unlock */
-	VOMIT_ON_FAILURE(pthread_mutex_unlock(&s_request_queue_lock));
+
+    /* Take our lock */
+    scoped_lock lock(s_request_queue_lock);
     
+    /* Add to the queue */
+    add_to_queue(req);
+    
+    /* Spawn a thread if necessary */
+    iothread_spawn_if_needed();
     return 0;
 }
 
@@ -174,6 +166,7 @@ int iothread_port(void) {
 }
 
 void iothread_service_completion(void) {
+    ASSERT_IS_MAIN_THREAD();
 	ThreadIndex_t threadIdx = (ThreadIndex_t)-1;
 	VOMIT_ON_FAILURE(! read(iothread_port(), &threadIdx, sizeof threadIdx));
 	assert(threadIdx < IO_MAX_THREADS);
@@ -201,3 +194,11 @@ void iothread_service_completion(void) {
 	iothread_spawn_if_needed();
 	VOMIT_ON_FAILURE(pthread_mutex_unlock(&s_request_queue_lock));
 }
+
+void iothread_drain_all(void) {
+    ASSERT_IS_MAIN_THREAD();
+    ASSERT_IS_NOT_FORKED_CHILD();    
+    while (s_active_thread_count > 0) {
+        iothread_service_completion();
+    }
+}
diff --git a/iothread.h b/iothread.h
index 7619501ab..fe0f53006 100644
--- a/iothread.h
+++ b/iothread.h
@@ -22,11 +22,12 @@ int iothread_perform_base(int (*handler)(void *), void (*completionCallback)(voi
 */
 int iothread_port(void);
 
-/**
- Services one iothread competion callback.
-*/
+/** Services one iothread competion callback. */
 void iothread_service_completion(void);
 
+/** Cancels all outstanding requests and waits for all iothreads to terminate. */
+void iothread_drain_all(void);
+
 /** Helper template */
 template<typename T>
 int iothread_perform(int (*handler)(T *), void (*completionCallback)(T *, int), T *context) {