threads: implement pthread_create (#325)

* threads: implement `pthread_create`

As described in the [`wasi-threads`] proposal, this change implements
`pthread_create` using the new `wasi_thread_spawn(void *arg)` API. As
described there, `wasi-libc` exports the thread entry point with the
expected name, `wasi_thread_start`, and then unwraps the passed argument
`struct` to invoke the user function with the user argument `struct`.

[`wasi-threads`]: WebAssembly/wasi-threads#5

Previously, the TID was only passed to the child thread entry point; the
parent thread was forced to wait until the child thread set the TID in
the pthread structure. With this change, the TID will be passed not only
to the child thread but also returned to the parent thread, so that
either side can make progress. The `i32.store` becomes an
`i32.atomic.store` to avoid concurrent writes.

Author: abrown

Makefile

@@ -203,6 +203,7 @@ LIBC_TOP_HALF_MUSL_SOURCES += \
         thread/pthread_condattr_init.c \
         thread/pthread_condattr_setclock.c \
         thread/pthread_condattr_setpshared.c \
+        thread/pthread_create.c \
         thread/pthread_mutex_consistent.c \
         thread/pthread_mutex_destroy.c \
         thread/pthread_mutex_init.c \
@@ -229,6 +230,7 @@ LIBC_TOP_HALF_MUSL_SOURCES += \
         thread/pthread_rwlockattr_destroy.c \
         thread/pthread_rwlockattr_init.c \
         thread/pthread_rwlockattr_setpshared.c \
+        thread/pthread_setcancelstate.c \
         thread/pthread_testcancel.c \
         thread/sem_destroy.c \
         thread/sem_getvalue.c \
@@ -237,7 +239,6 @@ LIBC_TOP_HALF_MUSL_SOURCES += \
         thread/sem_timedwait.c \
         thread/sem_trywait.c \
         thread/sem_wait.c \
-        thread/pthread_setcancelstate.c \
     )
 endif
 

expected/wasm32-wasi/posix/defined-symbols.txt

@@ -11,6 +11,7 @@ __EINVAL
 __ENOMEM
 __SIG_ERR
 __SIG_IGN
+__acquire_ptc
 __aio_close
 __asctime_r
 __assert_fail
@@ -41,6 +42,7 @@ __des_setkey
 __do_cleanup_pop
 __do_cleanup_push
 __do_des
+__do_orphaned_stdio_locks
 __duplocale
 __env_rm_add
 __exp2f_data
@@ -182,6 +184,8 @@ __private_cond_signal
 __progname
 __progname_full
 __pthread_cond_timedwait
+__pthread_create
+__pthread_exit
 __pthread_mutex_lock
 __pthread_mutex_timedlock
 __pthread_mutex_trylock
@@ -196,11 +200,15 @@ __pthread_rwlock_unlock
 __pthread_rwlock_wrlock
 __pthread_setcancelstate
 __pthread_testcancel
+__pthread_tsd_main
+__pthread_tsd_run_dtors
+__pthread_tsd_size
 __putenv
 __qsort_r
 __rand48_step
 __random_lockptr
 __reallocarray
+__release_ptc
 __rem_pio2
 __rem_pio2_large
 __rem_pio2f
@@ -257,6 +265,9 @@ __tanl
 __testcancel
 __timedwait
 __timedwait_cp
+__tl_lock
+__tl_sync
+__tl_unlock
 __tm_to_secs
 __tm_to_tzname
 __tolower_l
@@ -322,6 +333,7 @@ __wasi_sock_accept
 __wasi_sock_recv
 __wasi_sock_send
 __wasi_sock_shutdown
+__wasi_thread_spawn
 __wasilibc_access
 __wasilibc_cwd
 __wasilibc_cwd_lock
@@ -948,6 +960,8 @@ pthread_condattr_destroy
 pthread_condattr_init
 pthread_condattr_setclock
 pthread_condattr_setpshared
+pthread_create
+pthread_exit
 pthread_mutex_consistent
 pthread_mutex_destroy
 pthread_mutex_getprioceiling
@@ -1212,6 +1226,7 @@ vswprintf
 vswscanf
 vwprintf
 vwscanf
+wasi_thread_start
 wcpcpy
 wcpncpy
 wcrtomb

expected/wasm32-wasi/posix/undefined-symbols.txt

@@ -1,4 +1,7 @@
 __addtf3
+__copy_tls
+__default_guardsize
+__default_stacksize
 __divtf3
 __eqtf2
 __extenddftf2
@@ -56,6 +59,7 @@ __imported_wasi_snapshot_preview1_sock_accept
 __imported_wasi_snapshot_preview1_sock_recv
 __imported_wasi_snapshot_preview1_sock_send
 __imported_wasi_snapshot_preview1_sock_shutdown
+__imported_wasi_snapshot_preview2_thread_spawn
 __letf2
 __lock
 __lockfile
@@ -64,6 +68,7 @@ __main_argc_argv
 __netf2
 __stack_pointer
 __subtf3
+__thread_list_lock
 __tls_base
 __trunctfdf2
 __trunctfsf2

libc-bottom-half/headers/public/wasi/api.h

@@ -2089,6 +2089,25 @@ __wasi_errno_t __wasi_sock_shutdown(
 ) __attribute__((__warn_unused_result__));
 /** @} */
 
+#ifdef _REENTRANT
+/**
+ * Request a new thread to be created by the host.
+ *
+ * The host will create a new instance of the current module sharing its
+ * memory, find an exported entry function--`wasi_thread_start`--, and call the
+ * entry function with `start_arg` in the new thread.
+ *
+ * @see https://github.com/WebAssembly/wasi-threads/#readme
+ */
+__wasi_errno_t __wasi_thread_spawn(
+    /**
+     * A pointer to an opaque struct to be passed to the module's entry
+     * function.
+     */
+    void *start_arg
+)  __attribute__((__warn_unused_result__));
+#endif
+
 #ifdef __cplusplus
 }
 #endif

libc-bottom-half/sources/__wasilibc_real.c

@@ -659,3 +659,14 @@ __wasi_errno_t __wasi_sock_shutdown(
     return (uint16_t) ret;
 }
 
+#ifdef _REENTRANT
+int32_t __imported_wasi_snapshot_preview2_thread_spawn(int32_t arg0) __attribute__((
+    __import_module__("wasi_snapshot_preview2"),
+    __import_name__("thread_spawn")
+));
+
+__wasi_errno_t __wasi_thread_spawn(void* start_arg) {
+	int32_t ret = __imported_wasi_snapshot_preview2_thread_spawn((int32_t) start_arg);
+    return (uint16_t) ret;
+}
+#endif