bionic: pthread: use private futexes by default for mutexes and condvars

Private futexes are a recent kernel addition: faster futexes that cannot be
shared between processes. This patch uses them by default, unless the PROCESS_SHARED
attribute flag is used when creating a mutex and/or conditional variable.

Also introduces pthread_condattr_init/destroy/setpshared/getpshared.

Change-Id: I3a0e2116f467072b046524cb5babc00e41057a53

1 files changed, 37 insertions, 0 deletions

diff --git a/libc/arch-x86/bionic/atomics_x86.c b/libc/arch-x86/bionic/atomics_x86.c
index b7b20e6..d6e3247 100644
--- a/libc/arch-x86/bionic/atomics_x86.c
+++ b/libc/arch-x86/bionic/atomics_x86.c
@@ -60,6 +60,43 @@ int __futex_wake(volatile void *ftx, int count)
     return ret;
 }
 
+/* Private futexes belong to a single address space and cannot be
+ * shared among processes. They are however significantly faster to
+ * operate than standard futexes.
+ */
+#define FUTEX_PRIVATE_FLAG  128
+#define FUTEX_WAIT_PRIVATE  (FUTEX_WAIT|FUTEX_PRIVATE_FLAG)
+#define FUTEX_WAKE_PRIVATE  (FUTEX_WAKE|FUTEX_PRIVATE_FLAG)
+
+int __futex_wait_private(volatile void *ftx, int val)
+{
+    int ret;
+    asm volatile (
+        "int $0x80;"
+        : "=a" (ret)
+        : "0" (FUTEX_SYSCALL),
+          "b" (ftx),
+          "c" (FUTEX_WAIT_PRIVATE),
+          "d" (val),
+          "S" (0)
+    );
+    return ret;
+}
+
+int __futex_wake_private(volatile void *ftx, int count)
+{
+    int ret;
+    asm volatile (
+        "int $0x80;"
+        : "=a" (ret)
+        : "0" (FUTEX_SYSCALL),
+          "b" (ftx),
+          "c" (FUTEX_WAKE_PRIVATE),
+          "d" (count)
+    );
+    return ret;
+}
+
 int __atomic_cmpxchg(int old, int new, volatile int* addr) {
     int xchg;
     asm volatile (