From 788df5f556dc950c63599db1fb9416193991e93a Mon Sep 17 00:00:00 2001
From: Ryan Fleury <ryan.j.fleury@gmail.com>
Date: Tue, 12 Aug 2025 10:12:05 -0700
Subject: [PATCH] os: barrier

---
 src/os/core/linux/os_core_linux.c | 66 ++++++++++++++++++++++++-------
 src/os/core/linux/os_core_linux.h |  2 +
 src/os/core/os_core.h             |  7 +++-
 src/os/core/win32/os_core_win32.c | 26 ++++++++++++
 src/os/core/win32/os_core_win32.h |  2 +
 5 files changed, 87 insertions(+), 16 deletions(-)

diff --git a/src/os/core/linux/os_core_linux.c b/src/os/core/linux/os_core_linux.c
index d8ded967..c61fa270 100644
--- a/src/os/core/linux/os_core_linux.c
+++ b/src/os/core/linux/os_core_linux.c
@@ -1091,14 +1091,18 @@ internal OS_Handle
 os_semaphore_alloc(U32 initial_count, U32 max_count, String8 name)
 {
   OS_Handle result = {0};
-  if (name.size > 0) {
+  if (name.size > 0)
+  {
     // TODO: we need to allocate shared memory to store sem_t
     // NotImplemented;
-  } else {
+  }
+  else
+  {
     sem_t *s = mmap(0, sizeof(*s), PROT_READ|PROT_WRITE, MAP_PRIVATE|MAP_ANONYMOUS, -1, 0);
     AssertAlways(s != MAP_FAILED);
     int err = sem_init(s, 0, initial_count);
-    if (err == 0) {
+    if(err == 0)
+    {
       result.u64[0] = (U64)s;
     }
   }
@@ -1127,17 +1131,19 @@ os_semaphore_close(OS_Handle semaphore)
 internal B32
 os_semaphore_take(OS_Handle semaphore, U64 endt_us)
 {
+  // TODO(rjf): we need to use `sem_timedwait` here.
   AssertAlways(endt_us == max_U64);
-  for (;;) {
+  for(;;)
+  {
     int err = sem_wait((sem_t*)semaphore.u64[0]);
-    if (err == 0) {
+    if(err == 0)
+    {
       break;
-    } else {
-      if (errno == EAGAIN) {
-        continue;
-      }
     }
-    InvalidPath;
+    else if(errno == EAGAIN)
+    {
+      continue;
+    }
     break;
   }
   return 1;
@@ -1146,20 +1152,50 @@ os_semaphore_take(OS_Handle semaphore, U64 endt_us)
 internal void
 os_semaphore_drop(OS_Handle semaphore)
 {
-  for (;;) {
+  for(;;)
+  {
     int err = sem_post((sem_t*)semaphore.u64[0]);
-    if (err == 0) {
+    if(err == 0)
+    {
       break;
-    } else {
-      if (errno == EAGAIN) {
+    }
+    else
+    {
+      if(errno == EAGAIN)
+      {
         continue;
       }
     }
-    InvalidPath;
     break;
   }
 }
 
+//- rjf: barriers
+
+internal OS_Handle
+os_barrier_alloc(U64 count)
+{
+  OS_LNX_Entity *entity = os_w32_entity_alloc(OS_LNX_EntityKind_Barrier);
+  pthread_barrier_init(&entity->barrier, count);
+  OS_Handle result = {IntFromPtr(entity)};
+  return result;
+}
+
+internal void
+os_barrier_release(OS_Handle barrier)
+{
+  OS_LNX_Entity *entity = (OS_LNX_Entity*)PtrFromInt(barrier.u64[0]);
+  pthread_barrier_destroy(&entity->barrier);
+  os_lnx_entity_release(entity);
+}
+
+internal void
+os_barrier_wait(OS_Handle barrier)
+{
+  OS_LNX_Entity *entity = (OS_LNX_Entity*)PtrFromInt(barrier.u64[0]);
+  pthread_barrier_wait(&entity->barrier);
+}
+
 ////////////////////////////////
 //~ rjf: @os_hooks Dynamically-Loaded Libraries (Implemented Per-OS)
 
diff --git a/src/os/core/linux/os_core_linux.h b/src/os/core/linux/os_core_linux.h
index 1770d239..4b345a4b 100644
--- a/src/os/core/linux/os_core_linux.h
+++ b/src/os/core/linux/os_core_linux.h
@@ -67,6 +67,7 @@ typedef enum OS_LNX_EntityKind
   OS_LNX_EntityKind_Mutex,
   OS_LNX_EntityKind_RWMutex,
   OS_LNX_EntityKind_ConditionVariable,
+  OS_LNX_EntityKind_Barrier,
 }
 OS_LNX_EntityKind;
 
@@ -90,6 +91,7 @@ struct OS_LNX_Entity
       pthread_cond_t cond_handle;
       pthread_mutex_t rwlock_mutex_handle;
     } cv;
+    pthread_barrier_t barrier;
   };
 };
 
diff --git a/src/os/core/os_core.h b/src/os/core/os_core.h
index 415bb662..158c5185 100644
--- a/src/os/core/os_core.h
+++ b/src/os/core/os_core.h
@@ -299,7 +299,12 @@ internal void      os_semaphore_release(OS_Handle semaphore);
 internal OS_Handle os_semaphore_open(String8 name);
 internal void      os_semaphore_close(OS_Handle semaphore);
 internal B32       os_semaphore_take(OS_Handle semaphore, U64 endt_us);
-internal void      os_semaphore_drop(OS_Handle semaphore);
+internal void      os_semaphore_drop(OS_Handle semaphore);
+
+//- rjf: barriers
+internal OS_Handle os_barrier_alloc(U64 count);
+internal void      os_barrier_release(OS_Handle barrier);
+internal void      os_barrier_wait(OS_Handle barrier);
 
 //- rjf: scope macros
 #define OS_MutexScope(mutex) DeferLoop(os_mutex_take(mutex), os_mutex_drop(mutex))
diff --git a/src/os/core/win32/os_core_win32.c b/src/os/core/win32/os_core_win32.c
index 65d7926d..175ad4f5 100644
--- a/src/os/core/win32/os_core_win32.c
+++ b/src/os/core/win32/os_core_win32.c
@@ -1352,6 +1352,32 @@ os_semaphore_drop(OS_Handle semaphore)
   ReleaseSemaphore(handle, 1, 0);
 }
 
+//- rjf: barriers
+
+internal OS_Handle
+os_barrier_alloc(U64 count)
+{
+  OS_W32_Entity *entity = os_w32_entity_alloc(OS_W32_EntityKind_Barrier);
+  InitializeSynchronizationBarrier(&entity->sb, count, -1);
+  OS_Handle result = {IntFromPtr(entity)};
+  return result;
+}
+
+internal void
+os_barrier_release(OS_Handle barrier)
+{
+  OS_W32_Entity *entity = (OS_W32_Entity*)PtrFromInt(barrier.u64[0]);
+  DeleteSynchronizationBarrier(&entity->sb);
+  os_w32_entity_release(entity);
+}
+
+internal void
+os_barrier_wait(OS_Handle barrier)
+{
+  OS_W32_Entity *entity = (OS_W32_Entity*)PtrFromInt(barrier.u64[0]);
+  EnterSynchronizationBarrier(&entity->sb, 0);
+}
+
 ////////////////////////////////
 //~ rjf: @os_hooks Dynamically-Loaded Libraries (Implemented Per-OS)
 
diff --git a/src/os/core/win32/os_core_win32.h b/src/os/core/win32/os_core_win32.h
index 22a21f80..4938a828 100644
--- a/src/os/core/win32/os_core_win32.h
+++ b/src/os/core/win32/os_core_win32.h
@@ -46,6 +46,7 @@ typedef enum OS_W32_EntityKind
   OS_W32_EntityKind_Mutex,
   OS_W32_EntityKind_RWMutex,
   OS_W32_EntityKind_ConditionVariable,
+  OS_W32_EntityKind_Barrier,
 }
 OS_W32_EntityKind;
 
@@ -66,6 +67,7 @@ struct OS_W32_Entity
     CRITICAL_SECTION mutex;
     SRWLOCK rw_mutex;
     CONDITION_VARIABLE cv;
+    SYNCHRONIZATION_BARRIER sb;
   };
 };