3 files changed, 66 insertions, 3 deletions

diff --git a/src/core/lib/support/cmdline.cc b/src/core/lib/support/cmdline.cc
index 49b34194c3..d2785d2f30 100644
--- a/src/core/lib/support/cmdline.cc
+++ b/src/core/lib/support/cmdline.cc
@@ -105,7 +105,7 @@ void gpr_cmdline_add_flag(gpr_cmdline* cl, const char* name, const char* help,
 }
 
 void gpr_cmdline_add_string(gpr_cmdline* cl, const char* name, const char* help,
-                            char** value) {
+                            const char** value) {
   add_arg(cl, name, help, ARGTYPE_STRING, value);
 }
 
diff --git a/src/core/lib/support/mpscq.cc b/src/core/lib/support/mpscq.cc
index db25f24264..b270777d5c 100644
--- a/src/core/lib/support/mpscq.cc
+++ b/src/core/lib/support/mpscq.cc
@@ -31,11 +31,12 @@ void gpr_mpscq_destroy(gpr_mpscq* q) {
   GPR_ASSERT(q->tail == &q->stub);
 }
 
-void gpr_mpscq_push(gpr_mpscq* q, gpr_mpscq_node* n) {
+bool gpr_mpscq_push(gpr_mpscq* q, gpr_mpscq_node* n) {
   gpr_atm_no_barrier_store(&n->next, (gpr_atm)NULL);
   gpr_mpscq_node* prev =
       (gpr_mpscq_node*)gpr_atm_full_xchg(&q->head, (gpr_atm)n);
   gpr_atm_rel_store(&prev->next, (gpr_atm)n);
+  return prev == &q->stub;
 }
 
 gpr_mpscq_node* gpr_mpscq_pop(gpr_mpscq* q) {
@@ -77,3 +78,37 @@ gpr_mpscq_node* gpr_mpscq_pop_and_check_end(gpr_mpscq* q, bool* empty) {
   *empty = false;
   return NULL;
 }
+
+void gpr_locked_mpscq_init(gpr_locked_mpscq* q) {
+  gpr_mpscq_init(&q->queue);
+  gpr_mu_init(&q->mu);
+}
+
+void gpr_locked_mpscq_destroy(gpr_locked_mpscq* q) {
+  gpr_mpscq_destroy(&q->queue);
+  gpr_mu_destroy(&q->mu);
+}
+
+bool gpr_locked_mpscq_push(gpr_locked_mpscq* q, gpr_mpscq_node* n) {
+  return gpr_mpscq_push(&q->queue, n);
+}
+
+gpr_mpscq_node* gpr_locked_mpscq_try_pop(gpr_locked_mpscq* q) {
+  if (gpr_mu_trylock(&q->mu)) {
+    gpr_mpscq_node* n = gpr_mpscq_pop(&q->queue);
+    gpr_mu_unlock(&q->mu);
+    return n;
+  }
+  return NULL;
+}
+
+gpr_mpscq_node* gpr_locked_mpscq_pop(gpr_locked_mpscq* q) {
+  gpr_mu_lock(&q->mu);
+  bool empty = false;
+  gpr_mpscq_node* n;
+  do {
+    n = gpr_mpscq_pop_and_check_end(&q->queue, &empty);
+  } while (n == NULL && !empty);
+  gpr_mu_unlock(&q->mu);
+  return n;
+}
diff --git a/src/core/lib/support/mpscq.h b/src/core/lib/support/mpscq.h
index 1cc9d89feb..fb22742050 100644
--- a/src/core/lib/support/mpscq.h
+++ b/src/core/lib/support/mpscq.h
@@ -20,6 +20,7 @@
 #define GRPC_CORE_LIB_SUPPORT_MPSCQ_H
 
 #include <grpc/support/atm.h>
+#include <grpc/support/sync.h>
 #include <stdbool.h>
 #include <stddef.h>
 
@@ -49,13 +50,40 @@ typedef struct gpr_mpscq {
 void gpr_mpscq_init(gpr_mpscq* q);
 void gpr_mpscq_destroy(gpr_mpscq* q);
 // Push a node
-void gpr_mpscq_push(gpr_mpscq* q, gpr_mpscq_node* n);
+// Thread safe - can be called from multiple threads concurrently
+// Returns true if this was possibly the first node (may return true
+// sporadically, will not return false sporadically)
+bool gpr_mpscq_push(gpr_mpscq* q, gpr_mpscq_node* n);
 // Pop a node (returns NULL if no node is ready - which doesn't indicate that
 // the queue is empty!!)
+// Thread compatible - can only be called from one thread at a time
 gpr_mpscq_node* gpr_mpscq_pop(gpr_mpscq* q);
 // Pop a node; sets *empty to true if the queue is empty, or false if it is not
 gpr_mpscq_node* gpr_mpscq_pop_and_check_end(gpr_mpscq* q, bool* empty);
 
+// An mpscq with a lock: it's safe to pop from multiple threads, but doing
+// only one thread will succeed concurrently
+typedef struct gpr_locked_mpscq {
+  gpr_mpscq queue;
+  gpr_mu mu;
+} gpr_locked_mpscq;
+
+void gpr_locked_mpscq_init(gpr_locked_mpscq* q);
+void gpr_locked_mpscq_destroy(gpr_locked_mpscq* q);
+// Push a node
+// Thread safe - can be called from multiple threads concurrently
+// Returns true if this was possibly the first node (may return true
+// sporadically, will not return false sporadically)
+bool gpr_locked_mpscq_push(gpr_locked_mpscq* q, gpr_mpscq_node* n);
+
+// Pop a node (returns NULL if no node is ready - which doesn't indicate that
+// the queue is empty!!)
+// Thread safe - can be called from multiple threads concurrently
+gpr_mpscq_node* gpr_locked_mpscq_try_pop(gpr_locked_mpscq* q);
+
+// Pop a node.  Returns NULL only if the queue was empty at some point after
+// calling this function
+gpr_mpscq_node* gpr_locked_mpscq_pop(gpr_locked_mpscq* q);
 #ifdef __cplusplus
 }
 #endif