Added semaphore with futex (hopefully fast)

examples/thread.c

@@ -12,9 +12,14 @@
 #include "libc/thread/self.h"
 #include "libc/thread/detach.h"
 #include "libc/thread/join.h"
+#include "libc/thread/nativesem.h"
 #include "libc/time/time.h"
 
+cthread_native_sem_t semaphore;
+
 int worker(void* arg) {
+  cthread_native_sem_signal(&semaphore);
+  
   cthread_t self = cthread_self();
   int tid = self->tid;
   sleep(1);
@@ -25,9 +30,12 @@ int worker(void* arg) {
 }
 
 int main() {
+  cthread_native_sem_init(&semaphore, 0);
+  
   cthread_t thread;
   int rc = cthread_create(&thread, NULL, &worker, NULL);
   if (rc == 0) {
+    cthread_native_sem_wait(&semaphore, 0, 0, NULL);
     //printf("thread created: %p\n", thread);
     sleep(1);
 #if 1
@@ -36,6 +44,8 @@ int main() {
     rc = cthread_detach(thread);
     sleep(2);
 #endif
+    cthread_native_sem_signal(&semaphore);
+    cthread_native_sem_wait(&semaphore, 0, 0, NULL);
     //printf("thread joined: %p -> %d\n", thread, rc);
   } else {
     printf("ERROR: thread could not be started: %d\n", rc);

libc/sysv/consts.sh

@@ -1928,13 +1928,13 @@ syscon	misc	DAY_5					0x02000b		11			11			10			10			0
 syscon	misc	DAY_6					0x02000c		12			12			11			11			0
 syscon	misc	DAY_7					0x02000d		13			13			12			12			0
 
-syscon	misc	FUTEX_PRIVATE_FLAG			0			0			0			0x80			0x80			0
+syscon	misc	FUTEX_PRIVATE_FLAG			128			0			0			0x80			0x80			0
-syscon	misc	FUTEX_REQUEUE				0			0			0			3			3			0
+syscon	misc	FUTEX_REQUEUE				3			0			0			3			3			0
-syscon	misc	FUTEX_REQUEUE_PRIVATE			0			0			0			131			131			0
+syscon	misc	FUTEX_REQUEUE_PRIVATE			131			0			0			131			131			0
 syscon	misc	FUTEX_WAIT				0			0			0			1			1			0
-syscon	misc	FUTEX_WAIT_PRIVATE			0			0			0			129			129			0
+syscon	misc	FUTEX_WAIT_PRIVATE			128			0			0			129			129			0
-syscon	misc	FUTEX_WAKE				0			0			0			2			2			0
+syscon	misc	FUTEX_WAKE				1			0			0			2			2			0
-syscon	misc	FUTEX_WAKE_PRIVATE			0			0			0			130			130			0
+syscon	misc	FUTEX_WAKE_PRIVATE			129			0			0			130			130			0
 
 syscon	misc	HOST_NOT_FOUND				1			1			1			1			1			0x2af9			# unix consensus
 syscon	misc	HOST_NAME_MAX				0x40			0			0			255			255			0

libc/sysv/consts/FUTEX_PRIVATE_FLAG.S

@@ -1,2 +1,2 @@
 #include "libc/sysv/consts/syscon.internal.h"
-.syscon misc,FUTEX_PRIVATE_FLAG,0,0,0,0x80,0x80,0
+.syscon misc,FUTEX_PRIVATE_FLAG,128,0,0,0x80,0x80,0

libc/sysv/consts/FUTEX_REQUEUE.S

@@ -1,2 +1,2 @@
 #include "libc/sysv/consts/syscon.internal.h"
-.syscon misc,FUTEX_REQUEUE,0,0,0,3,3,0
+.syscon misc,FUTEX_REQUEUE,3,0,0,3,3,0

libc/sysv/consts/FUTEX_REQUEUE_PRIVATE.S

@@ -1,2 +1,2 @@
 #include "libc/sysv/consts/syscon.internal.h"
-.syscon misc,FUTEX_REQUEUE_PRIVATE,0,0,0,131,131,0
+.syscon misc,FUTEX_REQUEUE_PRIVATE,131,0,0,131,131,0

libc/sysv/consts/FUTEX_WAIT_PRIVATE.S

@@ -1,2 +1,2 @@
 #include "libc/sysv/consts/syscon.internal.h"
-.syscon misc,FUTEX_WAIT_PRIVATE,0,0,0,129,129,0
+.syscon misc,FUTEX_WAIT_PRIVATE,128,0,0,129,129,0

libc/sysv/consts/FUTEX_WAKE.S

@@ -1,2 +1,2 @@
 #include "libc/sysv/consts/syscon.internal.h"
-.syscon misc,FUTEX_WAKE,0,0,0,2,2,0
+.syscon misc,FUTEX_WAKE,1,0,0,2,2,0

libc/sysv/consts/FUTEX_WAKE_PRIVATE.S

@@ -1,2 +1,2 @@
 #include "libc/sysv/consts/syscon.internal.h"
-.syscon misc,FUTEX_WAKE_PRIVATE,0,0,0,130,130,0
+.syscon misc,FUTEX_WAKE_PRIVATE,129,0,0,130,130,0

libc/thread/join.h

@@ -13,4 +13,3 @@ int cthread_join(cthread_t, int*);
 COSMOPOLITAN_C_END_
 #endif /* !(__ASSEMBLER__ + __LINKER__ + 0) */
 #endif /* COSMOPOLITAN_LIBC_THREAD_JOIN_H_ */
- 

libc/thread/nativesem.c

@@ -0,0 +1,112 @@
+/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
+│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :vi│
+╞══════════════════════════════════════════════════════════════════════════════╡
+│ Copyright 2020 Justine Alexandra Roberts Tunney                              │
+│                                                                              │
+│ Permission to use, copy, modify, and/or distribute this software for         │
+│ any purpose with or without fee is hereby granted, provided that the         │
+│ above copyright notice and this permission notice appear in all copies.      │
+│                                                                              │
+│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
+│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
+│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
+│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
+│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
+│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
+│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
+│ PERFORMANCE OF THIS SOFTWARE.                                                │
+╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/thread/nativesem.h"
+#include "libc/thread/yield.h"
+#include "libc/sysv/consts/nr.h"
+#include "libc/sysv/consts/futex.h"
+#include "libc/bits/atomic.h"
+
+#define CTHREAD_THREAD_VAL_BITS 32
+
+int cthread_native_sem_init(cthread_native_sem_t* sem, int count) {
+  sem->linux.count = count;
+  return 0;
+}
+int cthread_native_sem_destroy(cthread_native_sem_t* sem) {
+  (void)sem;
+  return 0;
+}
+
+int cthread_native_sem_signal(cthread_native_sem_t* sem) {
+  uint64_t count;
+  asm volatile("lock xadd\t%1, %0" : "+m"(sem->linux.count), "=r"(count) : "1"(1) : "cc");
+  
+  if ((count >> CTHREAD_THREAD_VAL_BITS)) {
+    int flags = FUTEX_WAKE;
+    
+    // WARNING: an offset of 4 bytes would be required on little-endian archs
+    void* wait_address = &sem->linux.count;
+    asm volatile (
+      "syscall"
+      :
+      : "a"(__NR_futex), "D"(wait_address), "S"(flags), "d"(1)
+      : "rcx", "r11", "cc", "memory"
+    );
+  }
+  
+  return 0;
+}
+
+int cthread_native_sem_wait_slow(cthread_native_sem_t* sem, const struct timespec* timeout) {
+  uint64_t count;
+  
+  // record current thread as waiter
+  asm volatile("lock xadd\t%1, %0" : "+m"(sem->linux.count), "=r"(count) : "1"((uint64_t)1 << CTHREAD_THREAD_VAL_BITS) : "cc");
+  
+  for (;;) {
+    // try to acquire the semaphore, as well as remove itself from waiters
+    if ((uint32_t)count > 0 && atomic_compare_exchange_weak(&sem->linux.count, count, count - 1 - ((uint64_t)1 << CTHREAD_THREAD_VAL_BITS))) break;
+    
+    int flags = FUTEX_WAIT;
+    register struct timespec* timeout_ asm("r10") = timeout;
+    
+    // WARNING: an offset of 4 bytes would be required on little-endian archs
+    void* wait_address = &sem->linux.count;
+    asm volatile (
+      "syscall"
+      :
+      : "a"(__NR_futex), "D"(wait_address), "S"(flags), "d"(count), "r"(timeout_)
+      : "rcx", "r11", "cc", "memory"
+    );
+    count = atomic_load(&sem->linux.count);
+  }
+  
+  return 0;
+}
+
+int cthread_native_sem_wait_spin_yield(cthread_native_sem_t* sem, uint64_t count, int yield, const struct timespec* timeout) {
+  // spin on yield
+  while (yield-- > 0) {
+    if ((count >> CTHREAD_THREAD_VAL_BITS) != 0) break; // a thread is already waiting in queue
+    if ((uint32_t)count > 0 && atomic_compare_exchange_weak(&sem->linux.count, count, count-1)) return 0;
+    cthread_yield();
+  }
+  
+  return cthread_native_sem_wait_slow(sem, timeout);
+}
+
+int cthread_native_sem_wait_spin(cthread_native_sem_t* sem, uint64_t count, int spin, int yield, const struct timespec* timeout) {
+  // spin on pause
+  while (spin-- > 0) {
+    if ((count >> CTHREAD_THREAD_VAL_BITS) != 0) break;
+    if ((uint32_t)count > 0 && atomic_compare_exchange_weak(&sem->linux.count, count, count-1)) return 0;
+    asm volatile ("pause");
+  }
+  
+  return cthread_native_sem_wait_spin_yield(sem, count, yield, timeout);
+}
+
+int cthread_native_sem_wait(cthread_native_sem_t* sem, int spin, int yield, const struct timespec* timeout) {
+  uint64_t count = atomic_load(&sem->linux.count);
+  
+  // uncontended
+  if ((count >> 32) == 0 && (uint32_t)count > 0 && atomic_compare_exchange_weak(&sem->linux.count, count, count-1)) return 0;
+  
+  return cthread_native_sem_wait_spin(sem, count, spin, yield, timeout);
+}

libc/thread/nativesem.h

@@ -0,0 +1,28 @@
+#ifndef COSMOPOLITAN_LIBC_THREAD_NATIVESEM_H_
+#define COSMOPOLITAN_LIBC_THREAD_NATIVESEM_H_
+#if !(__ASSEMBLER__ + __LINKER__ + 0)
+COSMOPOLITAN_C_START_
+
+/**
+ * @fileoverview native semaphore for implementation details
+ */
+
+typedef union cthread_native_sem_t {
+  struct {
+    uint64_t count;
+  } linux;
+} cthread_native_sem_t;
+
+struct timespec;
+
+int cthread_native_sem_init(cthread_native_sem_t*, int);
+int cthread_native_sem_destroy(cthread_native_sem_t*);
+
+int cthread_native_sem_wait(cthread_native_sem_t*, int, int, const struct timespec*);
+int cthread_native_sem_signal(cthread_native_sem_t*);
+
+
+COSMOPOLITAN_C_END_
+#endif /* !(__ASSEMBLER__ + __LINKER__ + 0) */
+#endif /* COSMOPOLITAN_LIBC_THREAD_SELF_H_ */ 
+ 

libc/thread/yield.c

@@ -0,0 +1,24 @@
+/*-*- mode:c;indent-tabs-mode:nil;c-basic-offset:2;tab-width:8;coding:utf-8 -*-│
+│vi: set net ft=c ts=2 sts=2 sw=2 fenc=utf-8                                :vi│
+╞══════════════════════════════════════════════════════════════════════════════╡
+│ Copyright 2020 Justine Alexandra Roberts Tunney                              │
+│                                                                              │
+│ Permission to use, copy, modify, and/or distribute this software for         │
+│ any purpose with or without fee is hereby granted, provided that the         │
+│ above copyright notice and this permission notice appear in all copies.      │
+│                                                                              │
+│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL                │
+│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED                │
+│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE             │
+│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL         │
+│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR        │
+│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER               │
+│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR             │
+│ PERFORMANCE OF THIS SOFTWARE.                                                │
+╚─────────────────────────────────────────────────────────────────────────────*/
+#include "libc/thread/yield.h"
+#include "libc/calls/calls.h"
+
+int cthread_yield(void) {
+  return sched_yield();
+}

libc/thread/yield.h

@@ -0,0 +1,14 @@
+#ifndef COSMOPOLITAN_LIBC_THREAD_YIELD_H_
+#define COSMOPOLITAN_LIBC_THREAD_YIELD_H_
+#if !(__ASSEMBLER__ + __LINKER__ + 0)
+COSMOPOLITAN_C_START_
+
+/**
+ * @fileoverview yield thread to OS scheduler
+ */
+
+int cthread_yield(void);
+
+COSMOPOLITAN_C_END_
+#endif /* !(__ASSEMBLER__ + __LINKER__ + 0) */
+#endif /* COSMOPOLITAN_LIBC_THREAD_YIELD_H_ */