[libc] add rwlock implementation

Author: Yifan Zhu

libc/config/config.json

@@ -49,6 +49,10 @@
     "LIBC_CONF_RAW_MUTEX_DEFAULT_SPIN_COUNT": {
       "value": 100,
       "doc": "Default number of spins before blocking if a mutex is in contention (default to 100)."
+    },
+    "LIBC_CONF_RWLOCK_DEFAULT_SPIN_COUNT": {
+      "value": 100,
+      "doc": "Default number of spins before blocking if a rwlock is in contention (default to 100)."
     }
   }
 }

libc/docs/configure.rst

@@ -36,6 +36,7 @@ to learn about the defaults for your platform and target.
     - ``LIBC_CONF_PRINTF_FLOAT_TO_STR_USE_MEGA_LONG_DOUBLE_TABLE``: Use large table for better printf long double performance.
 * **"pthread" options**
     - ``LIBC_CONF_RAW_MUTEX_DEFAULT_SPIN_COUNT``: Default number of spins before blocking if a mutex is in contention (default to 100).
+    - ``LIBC_CONF_RWLOCK_DEFAULT_SPIN_COUNT``: Default number of spins before blocking if a rwlock is in contention (default to 100).
     - ``LIBC_CONF_TIMEOUT_ENSURE_MONOTONICITY``: Automatically adjust timeout to CLOCK_MONOTONIC (default to true). POSIX API may require CLOCK_REALTIME, which can be unstable and leading to unexpected behavior. This option will convert the real-time timestamp to monotonic timestamp relative to the time of call.
 * **"string" options**
     - ``LIBC_CONF_MEMSET_X86_USE_SOFTWARE_PREFETCHING``: Inserts prefetch for write instructions (PREFETCHW) for memset on x86 to recover performance when hardware prefetcher is disabled.

libc/src/__support/threads/linux/CMakeLists.txt

@@ -22,11 +22,11 @@ add_header_library(
     libc.src.__support.time.linux.abs_timeout
 )
 
-set(raw_mutex_additional_flags)
+set(monotonicity_flags)
 if (LIBC_CONF_TIMEOUT_ENSURE_MONOTONICITY)
-  set(raw_mutex_additional_flags -DLIBC_COPT_TIMEOUT_ENSURE_MONOTONICITY=1)
+  set(monotonicity_flags -DLIBC_COPT_TIMEOUT_ENSURE_MONOTONICITY=1)
 else()
-  set(raw_mutex_additional_flags -DLIBC_COPT_TIMEOUT_ENSURE_MONOTONICITY=0)
+  set(monotonicity_flags -DLIBC_COPT_TIMEOUT_ENSURE_MONOTONICITY=0)
 endif()
 
 add_header_library(
@@ -42,8 +42,19 @@ add_header_library(
     libc.hdr.types.pid_t
   COMPILE_OPTIONS
     -DLIBC_COPT_RAW_MUTEX_DEFAULT_SPIN_COUNT=${LIBC_CONF_RAW_MUTEX_DEFAULT_SPIN_COUNT}
-    ${raw_mutex_additional_flags}
-  
+    ${monotonicity_flags}
+)
+
+add_header_library(
+  rwlock
+  HDRS
+    rwlock.h
+  DEPENDS
+    .futex_utils
+    .raw_mutex
+  COMPILE_OPTIONS
+    -DLIBC_COPT_RWLOCK_DEFAULT_SPIN_COUNT=${LIBC_CONF_RWLOCK_DEFAULT_SPIN_COUNT}
+    ${monotonicity_flags}
 )
 
 add_header_library(