1 // Copyright 2015 The Go Authors. All rights reserved.
2 // Use of this source code is governed by a BSD-style
3 // license that can be found in the LICENSE file.
4
5 //go:build unix
6
7 #include <pthread.h>
8 #include <errno.h>
9 #include <stdio.h>
10 #include <stdlib.h>
11 #include <string.h> // strerror
12 #include <time.h>
13 #include "libcgo.h"
14 #include "libcgo_unix.h"
15
16 static pthread_cond_t runtime_init_cond = PTHREAD_COND_INITIALIZER;
17 static pthread_mutex_t runtime_init_mu = PTHREAD_MUTEX_INITIALIZER;
18 static int runtime_init_done;
19
20 // pthread_g is a pthread specific key, for storing the g that binded to the C thread.
21 // The registered pthread_key_destructor will dropm, when the pthread-specified value g is not NULL,
22 // while a C thread is exiting.
23 static pthread_key_t pthread_g;
24 static void pthread_key_destructor(void* g);
25 uintptr_t x_cgo_pthread_key_created;
26 void (*x_crosscall2_ptr)(void (*fn)(void *), void *, int, size_t);
27
28 // The context function, used when tracing back C calls into Go.
29 static void (*cgo_context_function)(struct context_arg*);
30
31 void
32 x_cgo_sys_thread_create(void* (*func)(void*), void* arg) {
33 pthread_t p;
34 int err = _cgo_try_pthread_create(&p, NULL, func, arg);
35 if (err != 0) {
36 fprintf(stderr, "pthread_create failed: %s", strerror(err));
37 abort();
38 }
39 }
40
41 uintptr_t
42 _cgo_wait_runtime_init_done(void) {
43 void (*pfn)(struct context_arg*);
44
45 pthread_mutex_lock(&runtime_init_mu);
46 while (runtime_init_done == 0) {
47 pthread_cond_wait(&runtime_init_cond, &runtime_init_mu);
48 }
49
50 // The key and x_cgo_pthread_key_created are for the whole program,
51 // whereas the specific and destructor is per thread.
52 if (x_cgo_pthread_key_created == 0 && pthread_key_create(&pthread_g, pthread_key_destructor) == 0) {
53 x_cgo_pthread_key_created = 1;
54 }
55
56 // TODO(iant): For the case of a new C thread calling into Go, such
57 // as when using -buildmode=c-archive, we know that Go runtime
58 // initialization is complete but we do not know that all Go init
59 // functions have been run. We should not fetch cgo_context_function
60 // until they have been, because that is where a call to
61 // SetCgoTraceback is likely to occur. We are going to wait for Go
62 // initialization to be complete anyhow, later, by waiting for
63 // main_init_done to be closed in cgocallbackg1. We should wait here
64 // instead. See also issue #15943.
65 pfn = cgo_context_function;
66
67 pthread_mutex_unlock(&runtime_init_mu);
68 if (pfn != nil) {
69 struct context_arg arg;
70
71 arg.Context = 0;
72 (*pfn)(&arg);
73 return arg.Context;
74 }
75 return 0;
76 }
77
78 // Store the g into a thread-specific value associated with the pthread key pthread_g.
79 // And pthread_key_destructor will dropm when the thread is exiting.
80 void x_cgo_bindm(void* g) {
81 // We assume this will always succeed, otherwise, there might be extra M leaking,
82 // when a C thread exits after a cgo call.
83 // We only invoke this function once per thread in runtime.needAndBindM,
84 // and the next calls just reuse the bound m.
85 pthread_setspecific(pthread_g, g);
86 }
87
88 void
89 x_cgo_notify_runtime_init_done(void* dummy __attribute__ ((unused))) {
90 pthread_mutex_lock(&runtime_init_mu);
91 runtime_init_done = 1;
92 pthread_cond_broadcast(&runtime_init_cond);
93 pthread_mutex_unlock(&runtime_init_mu);
94 }
95
96 // Sets the context function to call to record the traceback context
97 // when calling a Go function from C code. Called from runtime.SetCgoTraceback.
98 void x_cgo_set_context_function(void (*context)(struct context_arg*)) {
99 pthread_mutex_lock(&runtime_init_mu);
100 cgo_context_function = context;
101 pthread_mutex_unlock(&runtime_init_mu);
102 }
103
104 // Gets the context function.
105 void (*(_cgo_get_context_function(void)))(struct context_arg*) {
106 void (*ret)(struct context_arg*);
107
108 pthread_mutex_lock(&runtime_init_mu);
109 ret = cgo_context_function;
110 pthread_mutex_unlock(&runtime_init_mu);
111 return ret;
112 }
113
114 // _cgo_try_pthread_create retries pthread_create if it fails with
115 // EAGAIN.
116 int
117 _cgo_try_pthread_create(pthread_t* thread, const pthread_attr_t* attr, void* (*pfn)(void*), void* arg) {
118 int tries;
119 int err;
120 struct timespec ts;
121
122 for (tries = 0; tries < 20; tries++) {
123 err = pthread_create(thread, attr, pfn, arg);
124 if (err == 0) {
125 pthread_detach(*thread);
126 return 0;
127 }
128 if (err != EAGAIN) {
129 return err;
130 }
131 ts.tv_sec = 0;
132 ts.tv_nsec = (tries + 1) * 1000 * 1000; // Milliseconds.
133 nanosleep(&ts, nil);
134 }
135 return EAGAIN;
136 }
137
138 static void
139 pthread_key_destructor(void* g) {
140 if (x_crosscall2_ptr != NULL) {
141 // fn == NULL means dropm.
142 // We restore g by using the stored g, before dropm in runtime.cgocallback,
143 // since the g stored in the TLS by Go might be cleared in some platforms,
144 // before this destructor invoked.
145 x_crosscall2_ptr(NULL, g, 0, 0);
146 }
147 }
148
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