[libc-commits] [libc] [libc][semaphore] Add post and wait operations for internal semaphore (PR #198959)

[Michael Jones via libc-commits]

================
@@ -9,30 +9,64 @@
 #ifndef LLVM_LIBC_SRC_SEMAPHORE_LINUX_SEMAPHORE_H
 #define LLVM_LIBC_SRC_SEMAPHORE_LINUX_SEMAPHORE_H
 
+#include "hdr/errno_macros.h"
+#include "hdr/time_macros.h"
+#include "hdr/types/clockid_t.h"
 #include "hdr/types/mode_t.h"
+#include "hdr/types/struct_timespec.h"
 #include "src/__support/CPP/atomic.h"
+#include "src/__support/CPP/limits.h"
 #include "src/__support/common.h"
 #include "src/__support/error_or.h"
+#include "src/__support/libc_assert.h"
 #include "src/__support/threads/futex_utils.h"
+#include "src/__support/time/abs_timeout.h"
 
 namespace LIBC_NAMESPACE_DECL {
 
+// Define SEM_VALUE_MAX as INT_MAX
+constexpr unsigned int SEM_VALUE_MAX =
+    static_cast<unsigned int>(cpp::numeric_limits<int>::max());
+
 class Semaphore {
   Futex value;
   unsigned int canary;
 
+  // Whether the semaphore is shared between processes.
+  bool is_shared;
+
   // A private constant canary used to detect use of uninitialized or
   // destroyed semaphores. Chose "SEM1" in ASCII (0x53='S', 0x45='E',
   // 0x4D='M', 0x31='1').
   static constexpr unsigned int SEM_CANARY = 0x53454D31U;
 
-public:
-  // TODO:
-  // Add the posting and waiting operations: sem_post, sem_wait,
-  //    sem_trywait, sem_timedwait, sem_clockwait.
+  // Helper function for timed blocking wait, wait for a required
+  // absolute timeout.
+  LIBC_INLINE int wait_until(internal::AbsTimeout timeout) {
+    while (trywait() != 0) {
+      auto wait_or = value.wait(/*expected=*/0, timeout, is_shared);
+      if (wait_or.has_value())
+        continue;
+
+      if (wait_or.error() == EAGAIN)
+        continue;
----------------
michaelrj-google wrote:

Combine
```suggestion
      if (wait_or.has_value() || (wait_or.error() == EAGAIN))
        continue;
```

https://github.com/llvm/llvm-project/pull/198959