From 9c89a7589c34ea6f40af5967a7a90434bad009a8 Mon Sep 17 00:00:00 2001
From: Mihir Singh <mihirsin@usc.edu>
Date: Sun, 28 Jul 2024 21:02:39 -0400
Subject: [PATCH] wait_state() first draft

---
 .../roc_pipeline/state_tracker.cpp            | 75 +++++++++++++++++--
 .../roc_pipeline/state_tracker.h              |  7 ++
 2 files changed, 75 insertions(+), 7 deletions(-)

diff --git a/src/internal_modules/roc_pipeline/state_tracker.cpp b/src/internal_modules/roc_pipeline/state_tracker.cpp
index a2e4a75b9..927eb8443 100644
--- a/src/internal_modules/roc_pipeline/state_tracker.cpp
+++ b/src/internal_modules/roc_pipeline/state_tracker.cpp
@@ -8,13 +8,50 @@
 
 #include "roc_pipeline/state_tracker.h"
 #include "roc_core/panic.h"
-
 namespace roc {
 namespace pipeline {
 
 StateTracker::StateTracker()
-    : active_sessions_(0)
-    , pending_packets_(0) {
+    : sem_(0)
+    , active_sessions_(0)
+    , pending_packets_(0)
+    , waiting_mask_(0) {
+}
+
+// This method should block until the state becomes any of the states specified by the
+// mask, or deadline expires. E.g. if mask is ACTIVE | PAUSED, it should block until state
+// becomes either ACTIVE or PAUSED. (Currently only two states are used, but later more
+// states will be needed). Deadline should be an absolute timestamp.
+
+// Questions:
+// - When should the function return true vs false
+bool StateTracker::wait_state(unsigned state_mask, core::nanoseconds_t deadline) {
+    waiting_mask_ = state_mask;
+    for (;;) {
+        // If no state is specified in state_mask, return immediately
+        if (state_mask == 0) {
+            return true;
+        }
+
+        if (get_state() & state_mask) {
+            waiting_mask_ = 0;
+            return true;
+        }
+
+        if (deadline >= 0 && deadline <= core::timestamp(core::ClockMonotonic)) {
+            waiting_mask_ = 0;
+            return false;
+        }
+
+        if (deadline >= 0) {
+            if (!sem_.timed_wait(deadline)) {
+                waiting_mask_ = 0;
+                return false;
+            }
+        } else {
+            sem_.wait();
+        }
+    }
 }
 
 sndio::DeviceState StateTracker::get_state() const {
@@ -49,22 +86,46 @@ size_t StateTracker::num_sessions() const {
 }
 
 void StateTracker::register_session() {
-    active_sessions_++;
+    if (active_sessions_++ == 0) {
+        signal_state_change();
+    }
 }
 
 void StateTracker::unregister_session() {
-    if (--active_sessions_ < 0) {
+    int prev_sessions = active_sessions_--;
+    if (prev_sessions == 0) {
         roc_panic("state tracker: unpaired register/unregister session");
+    } else if (prev_sessions == 1 && pending_packets_ == 0) {
+        signal_state_change();
     }
+
+    // if (--active_sessions_ < 0) {
+    //     roc_panic("state tracker: unpaired register/unregister session");
+    // }
 }
 
 void StateTracker::register_packet() {
-    pending_packets_++;
+    if (pending_packets_++ == 0 && active_sessions_ == 0) {
+        signal_state_change();
+    }
 }
 
 void StateTracker::unregister_packet() {
-    if (--pending_packets_ < 0) {
+    int prev_packets = pending_packets_--;
+    if (prev_packets == 0) {
         roc_panic("state tracker: unpaired register/unregister packet");
+    } else if (prev_packets == 1 && active_sessions_ == 0) {
+        signal_state_change();
+    }
+
+    // if (--pending_packets_ < 0) {
+    //     roc_panic("state tracker: unpaired register/unregister packet");
+    // }
+}
+
+void StateTracker::signal_state_change() {
+    if (waiting_mask_ != 0 && (get_state() & waiting_mask_)) {
+        sem_.post();
     }
 }
 
diff --git a/src/internal_modules/roc_pipeline/state_tracker.h b/src/internal_modules/roc_pipeline/state_tracker.h
index 80d8367fd..c97095116 100644
--- a/src/internal_modules/roc_pipeline/state_tracker.h
+++ b/src/internal_modules/roc_pipeline/state_tracker.h
@@ -14,7 +14,9 @@
 
 #include "roc_core/atomic.h"
 #include "roc_core/noncopyable.h"
+#include "roc_core/semaphore.h"
 #include "roc_core/stddefs.h"
+#include "roc_core/time.h"
 #include "roc_sndio/device_state.h"
 
 namespace roc {
@@ -32,6 +34,8 @@ class StateTracker : public core::NonCopyable<> {
     //! Initialize all counters to zero.
     StateTracker();
 
+    bool wait_state(unsigned state_mask, core::nanoseconds_t deadline);
+
     //! Compute current state.
     sndio::DeviceState get_state() const;
 
@@ -57,9 +61,12 @@ class StateTracker : public core::NonCopyable<> {
     void unregister_packet();
 
 private:
+    core::Semaphore sem_;
     core::Atomic<int> is_broken_;
     core::Atomic<int> active_sessions_;
     core::Atomic<int> pending_packets_;
+    core::Atomic<unsigned> waiting_mask_;
+    void signal_state_change();
 };
 
 } // namespace pipeline